Progammable Logic Controllers (PLCs)

Tools predate the stone age where sticks and rocks held by hand assist prehistoric humans in everyday tasks. These later evolved to wheels, levers, and pulleys. Although clocks and other mechanisms were the beginning of automation or the process of controlling a devise by using another system it wasn’t until electricity that automation rapidly takes off. Not that it was invented, electricity has been around forever, but it isn’t until the 1800’s that electricity began to be understood and harnessed providing for everyday needs such as lighting, communication and operating motors. So begins the industrial revolution where a number of devises can control or be controlled by others. The invention of vacuum tubes leads to development of much smaller semiconductor diodes and transistors replacing mechanical relays and begins the electronic revolution.

For industrial applications PLCs imitate relays. Relays are a mechanical device where an electric magnet is used to operate mechanical switches such as a light switch turning it on or off. Three and four way light switches make electrical contact in one position and open in the other and so with relays. These tiny integrated semiconductor chips are referred to as flip-flops in the computer world. Small ice cube relays generally include two three way switches. PLCs do not use mechanical switches but simulate them using computer programs.

Programmable Logic Controllers usually consist of four components: power supply, central processing unit (CPU), input/output modules, and a rack connecting them all together. The power supply converts conventional 120 volts to either 12 or 24 volts direct current more than adequate and safe to operate miniature components in the PLC but it is necessary to hook the output module to external mechanical relays capable of operating lights, solenoids and motors requiring much more current and voltage.

Some advantages of PLCs are they use less power to operate, their computer generated actuators can control more switching capabilities than two provided by most mechanical relays, switching can be changed from normally open or closed by programming instead of rewiring, and can be done in a lot less physical space. They also have the capability of being controlled by discrete or analog inputs. Discrete inputs are either on or off such as a light switches. Analog inputs measure the values of sensors such as temperature, flow and pressure and can be programmed to control the output at designated values. An example of this is cruise control on an automobile. The throttle is wide open until the car reaches a certain speed but when it does less gas is injected keeping its velocity where the operator desires. This closed loop is called negative feedback where the input is controlled by the output.

There are many types of programmable logic controllers offered by several manufacturers. Unless they are preprogrammed keep in mind that they are compatible with software available for the laptop being used.  The American National Standards Institute (ANSI) in the United States attempts to standardize manufacturers to regulations more straightforwardly understood by all users. However, they comply with the International Electrotechnical Commission headquartered in Geneva, Switzerland. IEC 61131-3 deals with PLC programs and acknowledges two textual languages and two graphical languages.

The two textural languages are Instruction List (IL) and Structural Text (ST). Structured Text is a complex language block structured for industrial control similar to C or PASCAL programming. Instruction List is less complicated similar to Assembly programming. Assembly language is understood by humans compared to Machine Language compatible with machines. As their names imply, they are a list of instructions written in computer code.

The two graphical languages are Ladder Diagrams and Functional Block Diagrams. It all starts with the Functional Block Diagram similar to Sequential Function Charts used by System Engineers and Software developers and similar to flow charts. Input variables are illustrated in boxes interconnected with arrows to operational parameters also shown in block diagrams. How it is all interconnected by graphical arrows determines different results. An algorithm can now be developed to decide on the best path to achieve the objective.

Ladder Diagrams are very similar to electrical schematic diagrams used for mechanical relays and are often used because they are more familiar to what electricians are used to. Instead of using normally open or closed relay contactors these computer programs depict make or break symbols although they operate much the same as contactors. Depending on how they are interconnected creates the integrated logic gates: NOT (open or closed switch with one input), AND (NO open contactors in series), OR (NO contactors in parallel), and XOR (a combination of both). The opposite being NAND, NOR and XNOR where normally closed relay contactors or computer generated break symbols are used. They can be visualized by using Truth Tables. The end result energizes an external relay coil (or not) to operate lights, motors, etc. depending on whether normally open or closed contactors in the output relay are physically wired allowing electrical current to apparatuses to achieve desired results. Depending on the inputs it might be desirable for some motors to run and others not, vice versa, or a combination of both. When dealing with water tanks for example the pump filling it depends on low level and pressure while the pump emptying it might operate when the tank is full or exceeds pressure and sensors on the system being fed calls for it.

In addition to a port on the central processing unit where a USB cable from a laptop with appropriate software can be plugged in many PLCs are compatible with HMIs (Human Machine Interface). These are generally small touch computer screens with a diagram showing the system to be monitored and controlled. They show tanks, wells and so on as well as schematic configurations of sensors, actuators, pumps motors, etc. with real-time values or whether they are running or not. Although they cannot change logic in PLCs, HMIs easily allow interaction between human operators and machines. Not only do they show data from sensors such as temperature, pressure, flow rate and levels but their values can be adjusted by operators controlling actuators and motors.

Remote Terminal Units (RTUs) can also be compatible with PLCs. They are microprocessors that transmit digital and analog data and interface similar to HMIs but by radio to a distributed control system or SCADA network using protocols such as Modbus and Ethernet/IP. Advanced technology allows this to be done using cell phones provided they have the appropriate application and access codes. SCADA is a control and acquisition system accessed worldwide. Although SCADA is convenient because operators need not be physically on site, it makes the system vulnerable to competitors wishing to disrupt it or demand ransomware.

Eberling@www.thndrsns.com

Operating Motors at Variable Speeds

Electric motors are used every day. Ones that easily come to mind are in refrigerators and freezers for pumping freon and heaters blowing warm air around. Not as apparent are those in CD/DVD players and computer hard disk drives. Cars technically use gas engines not discussed here. Household motors are relatively small and easy to start and stop protected by circuit breakers and fuses.

Larger motors are often necessary in commercial facilities. Industrial complexes generate electricity, process food, procure and dispense fuel. Motors can be substantial and harder to control.

Conventional Motor Starters
More current is needed to get a motor running than keep it up to speed particularly when under load. Starting currents can be six times a motor’s rated FLA (full load amperage) for a short time. Sparks created when a switch makes contact between wires or conductors providing electricity with ones feeding big motors can be significant and burn them up.

Electric motor starters use solenoids (electro-magnets) which when energized close contactors quickly. These magnets can be controlled by voltages and currents smaller than what motors require. A 480-volt, three phase motor with 65 FLA can be controlled by a 120-volt, single phase 15-amp circuit. Control circuits with lower ratings are safer to handle and allow pressure and other limit switches with smaller contacts and wires to start and stop large motors.

Electric starters rate in size under NEMA 1 to over 12 depending on horse power of motors. Bigger starters not only take more space but are more expensive. They use time delayed thermal overload devises allowing large starting currents, but trip if persisting over full load amperage.

Larger motors are rated 60 cycles per second, either single or three phase, as provided by utility companies in North America. Because frequency of electrical current going into and out of standard motor starters does not change, motors operate at constant revolutions per minute. They cannot run faster than designed, and if caused to go slower thermal overloads will stop them before damaged by heat. Size and speed of machines operated can be altered with different size pulleys and belts or gears.

Modern electronics devices can control apparatuses more precisely by varying speed of motors.

Advantages Controlling Motor Speed
Ramping a motor gradually to speed results in less wear and tear on it and equipment operated. Loaded conveyor belts incur less damage when rollers they’re pulled by don’t slip when quickly started. Same for fan belts. If a conveyor belt transferring potatoes to a storage bin is loaded by hand instead of a hopper with a couple of potatoes on the belt every few feet dropping at a very fast rate, it makes sense to slow the whole process down.

Electronic devices controlling motor drives no longer only switch on or off but monitor activity. They output 1 to 5 volts or 4 to 20 milli-amps as pressure increases and decreases or temperature goes up and down. Values don’t start at zero since no signal indicates monitors aren’t working correctly or a broken wire to central processing units which sound that alarm. These wires should be shielded and grounded at one end to drain off surrounding electrical interference. They may be smaller than #16 gauge but that can cause problems ensuring proper termination and conductivity.

Benefits to calibrated monitors are speeding a pump up on low pressure and slowing it down when higher instead of continually starting and stopping the pump motor or making a fan on a heating or cooling devise go faster or slower as temperature varies making it more constant in rooms.

Other advantages controlling speed has to do with motors themselves. Power factors being decimals significantly less than one are not desirable when supplying power to incandescent lights or motors. This occurs when sine wave frequency of current starts later lagging that of voltage. Slowing a motor down by decreasing frequency lessens this problem resulting in amperage more constant with horse power. Electricity a fan or pump motor uses is proportional to the mathematical cube of speed. Slowing them down by twenty percent uses fifty percent less energy. Ramping motors up to speed reduces high starting currents.

Variable Frequency Drives
Variable frequency drives (VFDs) regulate revolutions-per minute (speed) and rotational force (torque) of motors designed for alternating current by changing frequency and voltage to them. Drives are also often referred to as AC, variable speed (VSDs), adjustable frequency (AFDs), adjustable speed (ASDs), variable frequency converters (VFCs), inverter drives and micro-drives.

Some use voltage source conversion (VSI), current source conversion (CSI), load-commutated inversion (LCI) or pulse-width modulation (PWM) inverters. Depending on the application one type might be more desirable with higher efficiency, reduced cost and increasing power factors or lessen clogging and pulsating rotation of motor shafts. They all rectify alternating current into direct current to an inverter converting electricity back to ac again but with different frequencies and voltages depending on 4-20 milli-amp inputs affecting speed and torque. Computers in VFDs programmed by operators interpret inputs and amperage to achieve desired results.

Some variable frequency drives are designed to accept direct current from a power source and convert it to alternating current. Great for running ac motors by batteries charged from solar panels or in electric driven vehicles. Other VFDs are designed or programmed to convert single-phase alternating current if only available at locations by utility companies into three-phase for those motors and vise-versa.

Harmonic Distortion
Harmonics are often favorable in music. When a guitar string is pressed to the fret in the middle a higher note is achieved called a second harmonic. If pressed third way up or down different frequency vibrations occur called 3^rd order harmonics. The combination of different notes may make pleasant sounds.

Harmonics aren’t useful in electric circuits. Current in three phase circuits are meant to be balanced canceling each other out back to the power source thereby alleviating a fourth neutral wire. Generators produce three phase sine waves by armatures 120 degrees apart wound with wires revolving in magnetic fields sixty times a second. Intent is for VFDs to make perfect sine waves but changing frequency to vary motor speed is unaffordable with semi-conductor devices available now. Three phase motors do not have a neutral wire.

Rectifying alternating current into dc using capacitors and diodes has been around for a while but today computers can replicate sinusoidal waves based on differential calculus. Converting ac to dc by VFDs don’t require computer assistance but changing current back to ac again does. Information from computed sine waves are transmitted on high frequency carrier waves to full-wave bridge inverters made with diodes or insulated gate bipolar transistors. IGBTs are much larger than conventional transistors. Transistors are based on outdated vacuum tubes where trivial voltages from radio waves are amplified repeatedly until capable of driving audible speakers and TV screens. This made transistor radios smaller and powered by batteries.

Sine waves are simulated by space vector pulse-width modulation. IGBTs operate on a different principle called sinusoidal pulse-width modulation. Different frequencies of sine waves are converted into switching algorithms by computers which do not change maximum output voltage but allow transistors to produce varied square waves of equal amplitude. Minute increments of time called integers between pulses and their durations determine output voltage and current frequency. Carrier frequencies from computed sine waves should be greater than ten times (2,000 to 16,000 hz) power output frequencies. Square waves leaving inverters are pronounced and cumbersome. Six pulse rectification and inversion result in approximately 25% total harmonic distortion where 18 pulse creates around 5% THD with less clipping. Everything to do with electrical circuits and devices means more is better until size and cost are considered.

Harmonic Filters
Made with the same parts, motors are basically generators in reverse. If armatures rotating in magnetic fields produce electricity, then motors can convert it back to mechanical energy. Adverse effects running motors with distorted sine waves from VFDs are apparent. It is required by NEMA standards these motors be designed definite-purpose inverter fed duty and withstand high surge voltages, can run at low speeds without overheating, and endure 200% torque overload for one minute. It is desirable to dampen or mitigate harmonic power distortion before getting to inverter duty motors. Long wires from VFDs amplify distortion due to impedance. Shielded, flexible VFD cables are offered if longer lengths are necessary. Transformers being inductors themselves dampen irregularities to motors. Output filters run the risk of damaging drives. High carrier frequencies in drives create sparking in motor bearings resulting in their deterioration.

Not as critical to operation is harmonic distortion back-fed on transmission lines supplying VFDs. Line harmonics result when converting ac to dc with voltage and current distortion. Chopping or clipping sine waves leave voltage spikes. Considered negligible with small motors, large VFDs create distortion with other motors, lighting and electronic equipment connected to the line before them.

Utility companies require filters before feeding substantial inverter drives. Not a bad idea if the line also supplies your residence. Active filters inject opposite harmonics using diodes or IGBTs requiring computer control. More common are passive filters with inductors and capacitors dampening and draining distortion to ground and providing power factor corrections.

VFDs sometimes have an efficiency loss up to five percent producing some heat. Passive harmonic filters utilize resistors, inductors and capacitors considerably bigger than in electronic circuits. It is their purpose to burn off or drain unwanted power distortions. Size and more heat dissipation requires them in separate enclosures away from drives.

Dynamic Breaking
Motors are similar to generators. If motors run faster than power intends electricity is back fed into the supply. Because conventional motor starters open contactors when stopping motors, back-fed electricity has nowhere to go causing motors to stop faster. VFDs reduce speed or stop motors by decreasing current but back-fed energy remains in the system.

Some CSI and LCI type drives are Regenerative VFDs which recover breaking energy meant to return to the power source. If motors are sped-up and slowed down often there may be some economic advantage to recovering this energy provided a place to store it such as capacitors or batteries. Utility companies don’t want distorted power on their line.

Commonly used are dynamic breaks, and like filters drain to ground or burn off undesirable energy. Breaks get much hotter making it even more important putting them in separate enclosures.

Misconceptions
Measurement of horsepower of engines and motors was originally derived by actual horses. A weighted wagon an average size horse can pull a given distance and time became one horsepower. If weight doubled or half as much time needed to pull it, two horses are required. Two horses tethered to pull the wagon with original weight and speed means each horse works half as hard resulting in one horsepower. One linear mechanical horsepower is 33,000 foot-pounds per minute (550 ft-lbf/second) requiring 746 electrical watts (volts x amps).

Motors rotate, and linear movement converts to rotational torque equal to horsepower times 5252 divided by rpms. Motor designed for specified revolutions-per-minute equipped with larger pullies on their shafts pull loads at less speeds but higher torque. Lesser horsepower might now be needed than what the motor is rated.

One misapprehension is if a twenty-horsepower motor is only needed to run a pump or conveyor belt, then a forty-horsepower motor at half rpm can be operated by a 20 hp VFD. It takes more energy to ramp a large motor to speed and if the load exceeds 20 hp for some reason smaller VFDs might be damaged. Better to use a 40 hp VFD at half capacity to run a 40 hp motor with lesser loads.

Another misconception is utility transformers providing power can be half the size if a motor runs at half the speed. The same as the above applies. KVA ratings of single-phase transformers used to operate three-phase motors should be increased by the 1.73 conversion factor. A 20 hp, three phase motor fed single phase to harmonic filters and dynamic brakes means these are rated 20 hp when verified by manufacturers.

Article 430, Part X gives more information and installation requirements by the 2020 National Electric Code for Adjustable-Speed Drive Systems.

Future Uses
Many electronic inventions improve with time. As VFD technology becomes better it will be used more often in the future.

Eberling@www.thndrsns.com

Sizing Electric Wires

Theoretical physics has many possibilities, but the basic concept is all material and matter are made of molecules. Copper(CU) and aluminum(AL) atom configurations can be found in Chemistry’s Periodic Table. Water molecules (H2O) are made of two hydrogen and one oxygen atom bound together. Distilled water is a poor conductor resistive to electrical flow (current). Most tap or rain water contain minerals making it more conductive.

Basic electrical theory assumes atoms are somewhat similar to solar systems. Stars create gravitational pull keeping planets in orbit. Modern telescopes allow solar systems to be seen at great distances. Atoms are inversely miniature, invisible to electron microscopes. Atoms behave similar to solar systems with a nucleus greater in mass like the sun keeping electrons comparable to planets in orbit.

Pluto might pull from sun’s gravitational field easier than Mercury by outside forces. This is advantageous to electricity. Movement of electrons from one atom to another presently explain electrical current. Some atoms have electrons more easily displaced resulting in less electrical resistance. Gold is better and silver good but are not used except in smaller electronic devises due to cost. Copper suits larger applications. Aluminum has more resistance although cheaper.

All metals have some resistance to electricity without being at absolute zero ambient temperature. Some substances have considerably more resistance and are capable of withstanding heat used intentionally for light bulbs, cooking appliances and space heaters. Heat is undesirable in wires supplying power. Larger wires create less heat with more electrons flowing through them resulting in most produced power going to resistive and reactive devices. Sounds simple but gets complicated considering competitive cost and space allowed when installing wires and cables

Three things are fundamentally considered while sizing wires: metals they’re made of, types of insulation covering them, and minimum amperage that will cause over current devices protecting them to trip.

Amperage and De-rating
Table 8 in Chapter 9 of the National Electric Code offer physical dimensions for trade sizes. American Wire Gauge (AWG) is used for smaller wires #18 up to #4/0 AWG. Circular millimeters are used instead of square inches by other tables. Larger wires use circular mils (MCM) to designate size, identical for copper as aluminum. From these tables, ohms (resistance) per thousand feet are greater for aluminum usually needing them sized bigger than copper for a given current. Aluminum wires exposed to air oxidize causing conductive loss when insulation is removed for termination and requires a prohibitive compound coating applied in the field.

Article 310, Table 310.104(A) describes types of insulations with abbreviated letter designations and temperature ratings. These can be found more specifically and for other wires later in Chapter 3. Higher insulation ratings allow more amperage without damage. NM Romex found in Article 334 used in residences can be de-rated at 194 degrees Fahrenheit provided current does not exceed 140F ratings. Aluminum Underground Service-Entrance cable (USE) often supply these dwelling units.

Special allowance of 83% in 310.12 is made for these structures with services not less than 100 amps. Heat-resistant thermoplastic THHN and THWN-2 typically pulled in conduit go to 194 degrees F. W stands for moisture resistant insulation required in some locations including underground conduits. Wires are generally rated both categories marked on reels and insulation with their size.

The 2020 National Electric Code now requires one and two-family dwelling units to have outdoor emergency disconnecting means for all service conductors by Article 230.85 to provide safety to fire fighters and other emergency responders such as those called to assess gas leaks. Article 242 has been added requiring overvoltage and surge protection for these buildings as well.

Excluding exceptions found in other articles, 310.16 through 310.21 are used to determine wire size from corresponding tables. The first table is usually used unless for particular installations. Footnotes below tables are crucial. De-rating means wires must sometimes be larger than shown in tables made mandatory by Article 310.15.

The first de-rating pertain to ambient temperature corrections in spaces conduit, raceways and cables are installed. The equation provided can be used, but Tables 310.15(B)(1) & (2) make it simpler. Latter tables use higher ambient temperatures as basis for adjustment, but Table 310.16 revolves around 86 degrees F (30 Celsius). Warmer air outdoors or in rooms result in wires getting hotter. The far-right table column provide temperatures in Fahrenheit from below 50 to 185 degrees F. Adjustment for 78-86 F degrees is “1” making no difference when multiplied to amperages in Allowable Ampacity Tables. Temperatures below have greater adjustment and higher current allowance, but above 86F the correction becomes a decimal. Numbers multiplied by fractions become smaller.

A 12AWG wire with insulation rated 140 degrees F in an ambient temperature of 100F drops allowed current from 20 to 16.4 amps. The intended load must now be smaller, or wire area increased. Under the same circumstance type NM can be de-rated from 90-degree Celsius (194F) column capable of supplying a load pulling 27.3 amps, but only allowed up to 20 amps by Article 334.80. Attics can get hot during summer.

Circuit breakers and fuses are not intended to operate at full capacity for long periods of time. Total load is calculated at 125% times continuous loads and duties operating for more than three hours plus 100% of non-continuous loads.

The next adjustment factor for derating can be found in Section 310.15(C)(1) and corresponding table where number of current-carrying conductors in raceways, such as conduit, exceed three. Same applies for single and multiconductor cables not properly spaced apart for more than 24 inches. Those installed in cable trays are subject to Article 392.80 and sizing becomes dependent on type and distances spaced apart.

Heat generated by wires next to each other add up. Correction is similar to ambient temperature but depends on number of wires involved. Wires exposed to sunlight raised less than 7/8” above rooftops require additional 60F added to outdoor temperatures.

Circuits fall into three main categories. Service conductors are from the serving utility or other source to premise wiring systems. Section 90.2(B)(5) excuse installations by electric and communication utilities from adhering to the National Electric Code. Feeders are conductors between service equipment and final branch-circuit over current devices, commonly a panel with smaller breakers or fuses. Branch circuits go from there to outlets or devices to be operated. In no case can circuits be rated less than maximum load served, although 240.4(B) allows next higher standard ampere ratings found in Table 240.6(A) for services and feeders.

Not the case for branch circuits. Not only do wires need be at or above protection, but 240.4(D) requires them lower for #18 to #10AWG even if more amperage is allowed by higher temperature insulation. This does not mean higher values cannot be used for de-rating.

Dedicated branch circuits with less loads than wires are capable, like smoke detectors and alarms, are already de-rated.

Voltage-Drop
Beginning of Article 310.14 (Ampacities for Conductors 0-2,000 Volts), Informational Note No. 1 states voltage-drop is not taken into consideration, but references other Notes where recommendations are made. Insulation temperatures or number of wires are not considered when calculating voltage-drop. Three percent in either feeders or branch-circuits provide reasonable efficiency if their sum does not exceed five percent.

Voltage-drop is desirable in light bulb dimmers but results in poor efficiency for conductors feeding devices. It can be measured with instruments at the last device on a circuit provided others are operating at full capacity. Not a good idea to check for VD after wires are installed. Better to calculate it beforehand. Equations for it are not provided in the NEC.

Basic voltage drop formula is VD = 2 X Resistance (R) X Length one-way (L) X Amperage full load (I) / Circular Mils. Straight forward for direct-current but inductive and capacitive reactance in alternating circuits have an effect. Resistance(R) + Reactance(X) = Impedance(Z) now used instead of resistance. For close approximations, 12 can be used for copper wire and 18 for aluminum for both AC & DC, but Tables 8 & 9 in Chapter 9 get more specific. For a balanced load on a single-phase system with a common neutral wire the voltage-drop between it and load wires allow the number calculated to be divided by half. Not the case for three-phase systems but voltage-drop is now multiplied by 86.6%. Inductive motors and incandescent lighting cause current to lag voltage creating a power factor (PF), maybe 85% so voltage-drop would be divided by .85 making it higher. To determine percentage, voltage-drops are divided by total voltage available at the source X 100.

Many vacuum cleaners now require 15 amps at 120 volts which should be considered when installing 20-amp circuits to distant rooms. Continuous loads require breakers and wires be increased by 125%, or loads limited by 80% with 16 continuous amps. Wires normally being #12 over 100 feet might be increased to #10AWG to the first outlet ensuring more efficient operation.

Wires increased to compensate for either higher insulation temperature or voltage-drop are also de-rated for the other.

Neutrals
Neutral wires are also referred to as grounded conductors in the electrical code. In two-wire DC or AC circuits conductors are sized the same as load wires. Generators and inverters produce sine waves better explained in trigonometry or seen slow motion on an oscilloscope. Voltages produced increase and decrease, sixty times a second in North America, creating alternating-current. How these waves are positioned at and above or below zero potential determine size of grounded conductors.

Single phase generators and transformers produce one sine wave every 360-degree cycle. A three-wire circuit delivering power splits the wave in half by a grounded neutral being zero volts. Upper half of the wave is considered positive with electron flow going in one direction and lower half negative making electrons go the other way. Voltage potential between the two peaks still add up. In balanced loads power consumption is identical for upper half of the wave as the lower. Positive peaks require current going one way and negative peaks the other in common grounded conductors, so electrons do little in neutrals now not needed.

Completely balanced loads are uncommon in 240/120-volt branch circuit breaker panels and equipment. The intent is to make them so, but stands to reason not all devices operate at once. Large cooking appliances, clothes dryers, hot water tanks, baseboard heaters and motors rated 240 volts are for the most part balanced between the top and bottom part of the phase. 120-volt devices use either upper or lower part to ground. Hard to determine when all will be used at once making these combined loads impossible to balance.

Common grounded wires are allowed smaller than load wires to compensate cost and space in raceways for single phase service and feeder circuits. They are not allowed smaller than maximum unbalanced loads (Art. 220.61). Minimum size for feeders are found in Table 250.122 based on overcurrent ratings by Article 215.4 and Section 215.2(A)(2). Minimum sizes for common grounded conductors in services are provided by Table 250.102(C)(1) based on size of the largest ungrounded conductor required by Articles 230.42 & 250.24(C) but not smaller than 1/0 AWG for 100 amp or greater loads. Exceptions are made for parallel circuits.

Parallel circuits are when two or more smaller wires used in place of a bigger one, provided square area or circular mils add up equal to or larger than the bigger one they replace. Sometimes an advantage for wires over 250 MCM since their reals are heavy and they are difficult to bend in panels or junction boxes. Parallel wires must be installed in the same raceway as their load wires but the same wire lengths are necessary if in parallel raceways. In many parallel circuits, common neutrals cannot be reduced from those carrying loads.

Three phase generators and transformers produce three sine waves per 360-degree cycle, common in 208/120-volt panels and devices. Calculations depend on square root of 3 (1.732) and natural trigonometric sine function (reactive factor) for vectors 120 degrees apart (.866). Harmonics are created and it is recommended and required neutrals in delta or wye connected systems be sized not less than load wires.

Grounding and Bonding
Ground wires are often referred to as grounding conductors by the NEC. Because they don’t conduct electricity under normal operating conditions they’re allowed even smaller than neutrals. Their purpose is to trip breakers or fuses on short circuit or ground fault conditions where load wires accidently conduct to metal and ground. Since they supply no loads over current happens quickly and smaller ground wires don’t have sufficient time to heat up and cause damage.

Unlike neutrals which are only allowed and required to be grounded to earth at the main disconnecting means, more grounding paths bonded together and taken to earth the better provided they also go back to the main disconnect. Return via metal raceways bonded correctly can also be used. A separate grounding conductor is not needed back to the utility supplying power since grounding and grounded circuits are connected where service is delivered to the main.

Sizing equipment and raceway grounding conductors are addressed in Article 250.122 with allowable minimum sizes shown in Table 250.122 based on rating or setting of circuit overcurrent devices but not required larger than conductors supplying loads. If ungrounded wires are increased in size to compensate for insulation temperature corrections or voltage-drop, grounding conductors must be increased proportionately.

Table 250.66 provide sizes for grounding electrode conductors for ac systems, but exceptions are made to buried electrodes such as ground rods earlier in this article by (A) thru (C). Electrodes are not intended carry fault current back to the service neutral but provide an equal potential to earth (0 volts). Electrode grounding conductors might be larger or smaller than shown in the table, but minimum sizes are given to withstand physical damage.

Bonding connects various metals and grounding systems together addressed by Part V in 250. Intent is to conduct fault current back to the service usually requiring bigger bonding wires than electrode conductors by Table 250.102(C)(1) based on circular mils of the largest ungrounded conductor or combined parallel conductors. This table also pertains to bonding jumpers. Piping systems and exposed structural steel are a safety risk when conducting fault current and must carry full load currents back to service disconnecting means.

Tap Conductors
Taps defined in Article 240.2 take exception to requiring conductors being sized for over current devices ahead of them. Often sub-panels with lower overload protection are used next to service panels or other sub-panels distributing power to smaller loads. Reduced feeder taps not only lessen costs but accommodate minimum conductor bending radius found in Article 300.34 and in Article 408.55 for panels. Problems can result in panels with several big wires. It can be difficult installing dead fronts and shutting outer panel doors completely when they’re full of wires.

It is often desired to install large wires protected by main breakers capable of handling entire loads to gutters and tap smaller wires to sub-panels using split-bolt, crimp or multi-tap connectors. Taps cannot be smaller than allowed by sub-breakers they feed with only raceways now protecting them. Reduction in size depends on length from where they are tapped by Article 240.21 or Article 368.17 from busways. Equipment grounding conductors are still determined by Table 250.122, but not required larger than tap conductors (Art. 250.122(G)).

Tap conductors can sometimes be used for branch circuits allowed by Sections 210.19(A)(3) & (4) for household ranges, cooking appliances and some other loads. Branch circuit taps to motors are addressed in Articles 430.28 & 430.53(D).

Transformers
Transformers increase or decrease voltage from the supply (primary) side to load (secondary) side. Amperage is adjusted proportionately by Power(KVA) / Voltage(V) = Current(I). Depending on physical size transformers are only capable of handling limited power as rated. In all cases, transformers must have adequate overcurrent protection on primary sides. When voltage is stepped-up by 2, available current delivered is divided by 2. Wires leaving these transformers then do not have to be as big as supplied. Voltage stepped-down causes the opposite effect.

Transformers are often considered a power source similar to utilities or generators. If grounded wires supplying them, which many don’t have, aren’t connected to neutrals leaving transformers then they are considered separately derived systems. Neutrals leaving must now be bonded to the grounding system.

Because transformers are protected on primary sides, overcurrent devices may not be needed for relatively short distances from the secondary considered tap wires discussed in Articles 240.4(F) and 240.21(C).

Motors
Motors have different rules. They take considerably more electricity to start than run. Starting happens quickly, and overcurrent protection is allowed greater for wires supplying motors than what they’re rated. Article 430 considers different types of motors and means of protection. Conductors must be increased 125% for continuous duty motors.

Tables 430.247 through 430.250 are used to determine full-load current based on horsepower ratings instead of nameplate values. Article 430.6(A) makes exception for motors with speeds less than 1,200 rpm, high torque, and multi-speed motors. Feeders and branch-circuit conductors are sized according to Article 310.15 provided they’re capable of carrying starting currents (Art. 430.52(B)).

Over-current protection for motor lead wires can be increased from requirements of Table 310.16 by Table 430.52. Non-time delay fuses and instantaneous circuit breakers can be much larger, but only for certain situations under Section 430.52(C)(3). Time-delay fuses and inverse time breakers have trip times inversely proportional to overcurrent. Large overcurrent trips them faster and wires do not need to be increased as much but still permit a 250% allowance for standard loads. Not much room in motor termination boxes for big supply wires.

Load Calculations
In all cases, protected wires must be capable providing current necessary to operate all devises. Load calculations for dwellings and residences are found In Article 220 and Informative Annex D. If arc welders, hot tubs, large chandeliers or electric vehicle charging systems addressed in Chapter 6, Special Equipment are desired, or might be, load calculations must be increased. Commercial and industrial complexes require panel schedules with sub-breaker ratings and intended loads (KVA). Intent is to balance breakers supplying loads most used by placing them on opposite sides of panels and phases.

Considerably more information is given by the 2020 National Electric Code. Table of Contents provide page numbers found at the bottom. The index uses article numbers easily accessed at top corners of pages.

Eberling@www.thndrsns.com

Wiring Lower Volt Systems

Not long-ago systems having 26 volts and below were exempt from the National Electric Code. They do not generate enough electrical current to do harm to humans considering the body’s resistance to current flow. Higher voltages do. The NEC has significantly changed opinions of lower volt circuits since then.

Automobiles are not in the code unless having a 120v alternating current or larger generator on them. Vehicles differ from normal wiring situations. Rubber tires prevent current from going to ground. Best to stay in cars made of metal during lightning storms. Earth is where lightning wants to go.

Cars and trucks can be used as examples for low volt systems. Most auto batteries are 12 volts and do little harm to us when also touching the metal chassis but can deliver more than 300 hundred amps when starting fuel engines. These batteries make large sparks when metal is placed between terminals. When changing batteries, the cable should be taken off the negative terminal first since a conductive metal wrench touching the vehicle from there makes no difference, that terminal being connected to the frame anyway. The wrench can now safely be used on the positive terminal because the return circuit to the battery from the frame has been removed from the negative terminal.

Small 1.5v household batteries connected (+) to (-) add up to make 12 volts dc or more and can be handled safely. A metal object touching them end to end creates a direct short but makes little spark. Because small batteries only produce so much energy they are referred to as power limited.

Many Types of Low Voltage Circuits
The index in the NEC makes clear definition for low voltage circuits as being an electromotive force 24 volts nominal or less found in Article 551 for to Recreational Vehicles & Parks. Some direction for installing low voltage wiring is there, but for the most part Article 720 must be referenced. This article pertains to Circuits and Equipment Operating at Less Than 50 Volts and requires conductors not to be smaller than 12 AWG copper or equivalent. Makes little sense for most lower volt installations until 720.2 is considered referencing exceptions in Other Articles.

Moderately complex when and how exceptions apply are discussed in Other Articles for Low Voltage Lighting, Health Care Facilities, Park Trailers, Floating Buildings, Pipe Organs, Electroplating, Solar Photovoltaic (PV) Systems, Remote-Control, Signaling, and Power-Limited Circuits, and Power-Limited Fire Alarm (PLFA) Circuits. Where smaller wires are allowed for home furnaces and air conditioning thermostats, doorbells and so forth is in Article 725 for Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits. Although Class 1 reduced power limited circuits are somewhat restricted, those for Class 2 and Class 3 are not and require either the device producing or converting electricity, as small batteries or transformers, be power limited or fused accordingly. Tables 11 (A) & (B) found in Chapter 9 can be used to calculate equipment power source and fuse ratings, but it’s easier when marked on equipment by manufacturers approved by United Laboratories (UL listed). Some Canadian standards apply.

Hazardous (Classified) Areas I, II & III
Concerning electricity, hazardous areas are where high concentrations of gases & vapors, combustible dust, or ignitable fibers or flying’s are or can be present in the atmosphere or on light fixtures and other equipment with hot surfaces. These substances result in explosions due to electrical sparks and fall into Classes, different from classes used for power limited circuits by using Roman numerals.

Hazardous Classes are further subdivided by Divisions depending on how great concentrations are likely to be and extent electrical material and equipment must be installed in them to ensure safety and prohibit damage. Prevalent in European models, Zones may be used instead of Divisions. Groups further determine concentrations needed for ignition of different types of gases, dusts or fibers. Industrial facilities, such as natural gas wells and refinement sites, determine boundaries between Divisions or Zones. Corporations are responsible if damage results if their boundaries don’t encompass the entire threat. Divisions are determined in Commercial services, like gas stations, later in Chapter 500.

Power limitations on lower voltage equipment and circuits in hazardous locations are more critical because tiny sparks can ignite explosions and fires. For this lower voltage equipment and wiring to be exempt from costly manufacturing and installation, they must also be Intrinsically Safe Systems with lower power limitations addressed in Article 504.

Optical Fiber Cables
Optical cables transmit light comparable to electricity through wires but any similarities stop there. Used for their own sake to illuminate medical operations or light up artificial Christmas trees, optic cables are usually manufactured for communication and data.

Electricity is transfer of electron energy in molecules present in tangible matter. Light is made of photons traveling faster in absence of molecules. It goes 186,000 miles per second in outer space. Light is immune to electromagnetic interference generated by electricity making optical cables efficient when placed beside conductive wires or themselves.

Optics includes laws of refraction and total internal reflection. Light is trapped in denser material surrounded by less provided there is a small angle of contact. For light to completely refract, this angle must be less than the critical angle determined by differences in mass. Diffusion causes irregularities from other than a completely smooth boundary. Optical cables can be made of many fibers the size of threads, thin enough to prevent light waves making contact from the inner core made of highly transparent flexible glass to surrounding cladding more than critical. Much data can be imposed on a single wave of light generated by lasers. Information is increased by many fibers and frequencies.

So why are optical fiber cables addressed in Chapter 7, Special Conditions by the National Electric Code since light has no known voltage? Transmitters and receivers interpreting this light do and cables are likely installed by electricians. Fundamentally there are two types of optic cables, nonconductive and conductive, the latter using metal jackets and wires for protection and strength to pull them in and hang in vertical risers. Hybrid cables have both electric wires and fibers. Optic cables can occupy the same conduits and cable trays as electric cables. Metal wires in optic cables need to be bonded and grounded. Types of cables are listed for various installations in Table 770.154(a) and (b). Another consideration is when they are installed in ducts used for environmental air, especially when used for heating.

Although no specific reference is made to family dwellings, optical cables are further discussed by Premise-Powered Broadband Communication Systems in Chapter 8.

Communication Systems
Residential and most commercial communication cables are low volt but not taken lightly by the NEC. In fact, Chapter 8 pertaining to them is the last chapter preceding Tables and Informative Annexes and is completely devoted to communication. This chapter is divided into five Articles depending how communication, TV, internet, etc. are provided. The NEC does not cover wireless devices regulated by the FCC.

Article 805 addresses Communication circuits as telephone land lines and is not all that complicated. Article 810 is for Radio and Television Equipment. It helps to understand how antennas work.

Antennas receive electromagnetic waves transmitted through air and are not to be mistaken for electromotive force (EMF) commonly known as voltage. Electromagnetic fields are generated by alternating current transferring energy from wires when coiled around an iron core in electromagnets and transformers. Energy also transfers between wires run next to each other. Electromagnetic waves are transmitted from ground towers and satellites outside earth’s atmosphere. Outer space is considered a vacuum.

This technology was used during WWI to receive Morse code in battlefields. Additional power was not needed for amplification by crystal radios. Electric flow results in voltage through resistive devises and small headphones were needed because voltage derived was small.

Antennas have become more complex collecting stronger electromagnetic waves of certain frequencies transmitted from a particular direction. Energy from batteries or a larger source is still required for amplification needed by radio and television power consumption. Further advancements allow large, circular antennas mounted on poles in the yard to receive satellite transmission by TV providers. Antennas are now smaller since electromagnetic fields are significantly stronger and more focused from satellites. Coaxial cable from antennas to receivers provide better results than wires not being wrapped in a jacket made of meshed wires or foil. Conductive jackets drain off outside wave interference when grounded from overhead transmission lines and higher volt wires providing power to devises using more current. Larger signal wires provide better reception, but due to ease of installation RG-6 Coax is commonly used.

Community Antenna Television and Radio Distribution (CATV) Systems are different in that electromagnetic waves are received by taller antennas and processed by receiving stations before distributed with overhead or buried cables to consumers. At first analog signals received from antennas were sent through coaxial cables but modern television technologies rely more on digital inputs converted by receiving stations. Hybrid cables incorporating optical fibers and electric signal wires are used as well by companies.

Powered Broadband Communication Systems aren’t so much different from CATV Systems except they’re more digital and deliver additional information and data with many frequencies. Network-Powered Broadband mostly rely on conventional electric cables. HDTV cables in buildings improve operation of devises. Premise-Powered Broadband Systems depend more on optical fibers.

Articles in Chapter 8 are divided into similar Parts. Cables are listed from Tables depending on installation, must be properly grounded, and determine insulation ratings for voltage and issues such as restricting fires from spreading rapidly in buildings.

Eberling@www.thndrsns.com

Ground Fault vs. Arc Fault Circuit Protection

An estimated 40,000 homes a year are damaged by electrical fires but how many pertain to electrical installations in the last thirty years? Companies make a lot of money betting this incident won’t happen in comparison to what they’re getting paid to insure them. Forty thousand home fires in the United States is considerably less than one percent. Additional electrical preventative measures are certainly beneficial to insurers by reducing number of claims without reducing premiums.

It would be great if everything is wired in metal conduit. Costly but chances of electrical fires would all but be eliminated. The National Electric Board are doing best to eliminate electrical fires by incorporating Arc Fault circuit protection in the code. There are advantages and disadvantages associated.

Ground Fault and Arc Fault have two things in common, reducing electrical hazards by means of electronic components which trip faster than standard breakers and protect against additional safety concerns. Standard circuit breakers and fuses trip during over currents and short circuits by heating metallic components in them. With fuses this metal dissolves completely breaking the electrical circuit requiring fuses to be replaced. When metal strips in circuit breakers get hot they bend causing their switches to trip but can be reset once the metal cools down. Current cannot exceed their ratings thereby protecting wiring and connected loads but they don’t reduce safety hazards caused by electricity flowing in smaller amounts during arc and ground fault circumstances.

Ground fault circuit interrupters are intended to eliminate electrocution to persons around metal appliances, water and associated metal pipes. Arc fault interrupters are intended to reduce fires caused by sparks in by protecting wiring in structures to and at habitable rooms. Just about everything in dwelling units including manufactured and mobile homes are required to have one of these protective devices and/or the other. Requirements and locations in dwelling units for Ground Fault are in Article 210.8 and Arc Fault in Article 210.12 in the 2020 National Electric Code. Commercial structures necessitate some ground fault but not necessarily arc fault since wiring is protected by additional means. Industrial establishments have other rules to follow.

Ground fault was first introduced and quickly caught on. GFIC protective devises measure current on wires to intended loads. In safe situations, amperage is the same on both load and neutral wires. But when some current returns to the breaker or receptacle through ground paths they trip. This fault current might be through a person when touching grounded metal or water possibly causing ventricular fibrillation commonly known as electrocution. Less than thirty milliamps through us can cause cardiac arrest. Electrical resistance in our bodies prohibits tripping even a five amp or smaller fuse.

Originally called Residual Current Devises (RCDs) have evolved into breakers also capable of over and short circuit current protection more commonly known as GFCIs. GFI receptacles are cheaper than GFIC breakers and protect cords and devices plugged into them.

Now Arc Fault Circuit Interrupters are also required by code. AFCI devices detect sparks in wiring causing heat and possibly fires. Arcing can be parallel (line to neutral), series (loose or broken wire), and ground arcing (line or neutral to ground). Making this requirement unique from ground fault is not only connected devises must be protected, but the entire circuits from service panels. Exceptions consider wiring to the first AFC receptacle protecting those downstream if in metal raceways or MC cable usually installed in commercial establishments. Plastic PVC conduit costing less is not allowed. AFC receptacles also require an over and short circuit breaker in electrical panels although this discussion gets complicated. Only Combination Type AFCI breakers protect against all three types of arcing in the entire circuit.

Two types of services for residences are available, single phase and three phase. Single phase most of us are familiar with consists of three wires, 240 volts phase to phase and 120 volts phase to neutral. When available at the service panel it can be delivered down line in a similar manner. Both GFI band AFI protectors cannot share neutrals with loads connected to the other phase in three-wire installations without tripping. Since ground fault does not pertain to entire circuits, three wires with a grounding conductor from a double pole breaker at the panel can be installed in a single Romex cable run across the house tapping the neutral for another circuit before connecting a GFI receptacle. AFCI protection includes the entire wiring making two separate neutrals necessary from separate AFCI breakers or installed in metal conduit and metal cable eliminating this protection to an AFCI receptacle. Four conductor Romex is hard to come by with two white neutral wires and inductance might present problems making two separate cables necessary.

Remote rural areas often have three phase building services since two-thirds current is required on these transmission lines needed to deliver adequate power. Reducing three phase high voltage to standard 240/120 volts for lighting and receptacles requires several transformers. Generally 208/120 volts is available for ranges, clothes dryers, hot water tanks, etc. Dealing with neutrals in single phase circuits is still the same although three phase services consists of four wires at the main breaker panel.

Early on ground fault devises weren’t all that dependable tripping for no apparent reason. For this reason they were not required for garage door openers or refrigerators and freezers in kitchens. GFICs have become more reliable and these exceptions no longer apply. Arc fault circuit interrupters are relatively new and nuisance tripping can still be a problem. Ground fault is only required for receptacles or connected loads but Arc fault includes switches, lights and other junction and outlet boxes. AFCI protectors should be designed to ignore smaller sparks in switches and motors but it might be best to turn devices such as vacuum cleaners, lamps, televisions and so forth off before plugging them in or pulling their cords out of receptacles to prevent these small sparks from tripping AFC circuits.

Some machines use solenoids to allow small currents from thermal protectors and other regulators to control motors rated at much more amperage. Solenoids are made with small mechanical switches called contactors operated by electromagnets. Contacts can corrode after extended use causing larger sparks and nuisance tripping by arc fault protectors. AFCI tripping can be devastating for alarm devises. Allowance is made for electronic smoke detectors and burglar alarms but power can be tripped inadvertently by other devices on the same circuit. Modern alarms have battery backup.

Oxygen machines used for medical reasons may have problems when incorporating mechanical solenoids possibly disrupting power provided by arc fault protectors. Maybe oxygen machines should be required to have battery backup at least making loud shrills like monoxide and smoke detectors upon loss of power. Not a bad idea anyway in case they lose power for any reason such as being unplugged or utility power outages.

Fresh food deteriorates without being cooled in refrigerators and freezers. Refrigeration requires substantial electrical consumption making battery backup unfeasible and auditable alarms do no good if no one is there. Some states have AFCI allowances for them.

Although arc fault devices provide some protection from fires caused by faulty wiring, they do not prevent them all. Fires can be caused by overheated conductors, possibly more so than sparking wires. Fires can result from wires being inadvertently or intentionally hooked to breakers larger than what they are rated for or loose connections under terminal screws and in wire nuts. Thermal creeping heats wires up damaging insulation and setting flammable material in contact with them on fire. Power Fault Circuit Interrupters detect voltage drop in circuits more than considered normal causing this excessive heat. To date PFCI protection has not been implemented by the NEC.

It would be great if all wiring were installed in metal conduit and boxes. Generally manufacturers, suppliers and contractors won’t argue with more revenue. Efficiency doesn’t necessarily apply without affordability. Electrical installation costs can be reduced by providing less circuits or smaller protected wires when allowed by code maybe affecting overall convenience of homeowner abodes.

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Property of Electrical Grounding

Electricity is hard to visualize. It can’t be seen or smelt, but to touch it can be painful if not deadly. In an attempt over the years to make easier to understand the way it works has been often compared to properties of water. Maybe a little absurd since water reacts to gravity which has no measurable effect on electricity.

Electrical current is the movement of electron energy from one molecule to the adjacent. Like billiard balls, energy impacted on the first ball hit transfers to the next and so on. The speed of the cue ball transfers from one ball to the others and if they’re in a straight row only the last one will move much. It happens quickly in a good conductor. Static electricity generated by dragging feet across a shag rug carpet is an exception. Lightning is the result of water molecules in clouds rubbing against each other with excess energy going to earth where it came from and will eventually return. Maybe or maybe not the result of gravity but then again earth generates this attraction.

The concept that generated electricity tends to go to earth, probably created by Benjamin Franklin’s kite experiment with static electricity, has been replaced. It is now known that electricity returns to its source being a generator, transformer or battery. Dirt makes a poor conductor although better when wet.

What does this have to do with electrical grounding, much less water since water ultimately responds to gravity? For the purposes of this comparison, earth must now be thought of as a generator, transformer or battery when comparing properties of water.

Given multiple paths, more water will go down the steepest slope although lesser amounts will still run down others. The same with electricity proportionately returning to its source through paths of least resistance. More will return through a copper wire than a human body. With that said, who wants any electricity going through their body? Larger voltages create more current to be distributed. If the steeper slope is dammed by a switch placed on the return path of the devise(s) using energy being turned off, or a loose wire, all the water will go down lesser slopes. Likewise, if the conductor supplying the resistive or reactive devise contacts a person before reaching this device intended to be operated, current will divide proportionately between its resistance and ours because the easy copper return path of the devise has now been partially blocked by the light, motor, heater and so forth.

The National Electric Code requires all exposed metal parts of an electrical circuit be grounded with a third conductor or metal raceway such as conduit going directly to its source. Not infallible since splices in it or connecting other metal enclosures might come loose but suppose it’s better than jumping out of an airplane without a reserve parachute. The intent is virtually all fault current will take this path with almost no resistance and trip the over current protective devise immediately like a waterfall.

The NEC can be somewhat confusing as the intended return path, often called the neutral, is referred to by it as the grounded conductor, and wires in the safety path required so all exposed metal parts of a circuit be grounded are referred to as grounding conductors.

That’s not to say earth can be taken out of consideration when designing electrical systems. Produced electricity tends to fluctuate and this variance in voltage is eliminated when tied to ground considered to have no voltage. Because dirt is a poor conductor, resistances in it may cause slight voltage differentials back to the delivering service equipment. Differences in electrical potential cause currents to flow through conductive paths. Fluctuations in voltage are even more critical in modern times. Computers don’t behave well when supplied with erratic voltages.

Grounding circuits must be isolated from grounded circuits at devices back to the source or some of the returning current might take the path through exposed metal parts, putting us right back where we started regarding safety. Once reaching the device creating the desired voltage, or its main disconnect switch, it is highly recommended they be bonded together there so the neutral branch conductors will have a constant zero potential at that location required to be grounded to earth.

It is clear in the NEC what grounding electrodes are to be used and bonded together. Buried building steel and metal water pipes of structures require larger bonding conductors since they are more likely to be energized by short circuits downstream and take that path back to the neutral bus bar in the main service panel. Rebar in concrete foundations only need a smaller bonding wire and a ground rod smaller yet since their only purpose is to eliminate voltage difference between ground and electrical service. Back in the day only one ground rod was used. Possibly due to modern electronic developments, when resistance between one rod and earth exceeds twenty-five ohms a second rod is required not less than six feet apart from the first bonded by a small number six bonding conductor. When in doubt, use a larger number two conductor good for ground rings.

Article 250 of the 2020 National Electric Code contains twenty-nine pages and addresses Grounding and Bonding requirements in much more detail.

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The National Electric Code Has Come a Long Way Over the Years
by Steve Eberling

 Back in the day, if something was wired and it worked you were considered an electrician. How things have changed.

The National Electric Code was first published in 1897. Back then the method of wiring was knob & tube consisting of porcelain posts supporting electrical wires several inches from what they were secured to in attics, basements and outer surfaces of ceilings and walls. Only two wires since grounding wasn’t deemed necessary. This was an easy way to install electricity in existing structures by owners that could afford it.

Electrical work according to the NEC then became required by the National Fire Protection Association. Structural fires were probably caused by wood and coal burning stoves or oil lamps but electric wires couldn’t be ruled out as the cause.

First introduced the NEC was only fifty-eight pages not very big at that, about 8” high by 5” wide possibly not so much as to prevent fires as to protect electricians from this liability. Since 1989 NEC included many more pages about the same size with additional installation requirements. The 2020 code is nine hundred 8 ½”X11” pages.

Likewise, in Colorado anyway, a test had to be taken in order to obtain a license to legally perform electrical work as a contractor, required for commercial or industrial work. Residential home owners being exempt. But once the test was passed as a residential, journeyman or master electrician you had it unless wanting to up-grade. In this state, it isn’t compulsory for a contractor to have a maters license to do electrical work provided they employ one. Back then a license allowed six apprentices to work under it but now it’s three. Additional testing was also required, arguably good because they kept getting more difficult to pass. Twenty-four hours of credited classes are now necessary every three years.

Due to additional requirements, it now costs quite a bit more for material and labor to wire residences as awhile back. More advanced products offer more protection against shock and fires but rising costs don’t necessarily mean structures work more efficiently. Explaining it all in detail becomes quite involved and necessitates an understanding of the National Electric Code and how electricity works.

For electricians involved for years in the trade it’s all complicated enough, but the bottom line is it might be overwhelming to many wanting to become electricians. Let’s face it, they are not doctors, lawyers or such and this skill requires vigorous labor.

Although NFPA 70E, Electrical Safety in the Workplace is not readily referenced in the National Electric Code (NFPA 70), it’s practices are becoming more mandatory requiring further material and time.