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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