Arc-Fault, Ground-Fault, and Dual-Function Circuit Breakers Explained
There’s no doubt that if you’re in the electrical field, you’ve heard the phrases “arc fault”, “dual function”, and “ground fault” a few times and been a bit confused about what the differences are, or if it even matters. Well my friends, this week we lay all questions and uncertainties to rest once and for all.
Arc Fault detection is a semi-recent requirement of the NEC but a vital one, as a large majority of house fires are caused by faulty wiring and the resulting arc faults. These arcs have been measured at 10,000 degrees Fahrenheit or more, easily setting fire to material nearby like wooden studs or insulation, making arc fault protection a necessity in every home. Arc Fault Circuit Interrupters “AFCIs” use computing technology to detect and protect an electrical circuit from unwanted arcing by monitoring current closely and disconnecting when irregularities occur. A combination AFCI or “CAFI” is a device that detects both parallel (hot to neutral, hot to ground, and neutral to ground) and series arcs (arcing between a single line caused by a loose connection or damaged conductor). You’re bound to find more CAFI breakers at stores and in the fields because the NEC no longer accepts non-combination AFCI breakers as proper arc fault protection in dwelling units without other supplemental AF protection devices.
Ground fault circuit interrupters or “GFCIs” are installed to protect from electrical shock by constantly measuring current from hot to neutral. When the device detects an imbalance signaling that current is flowing through a different conductor than neutral (like water, stone, or a human), it trips in milliseconds. An older study found that 47% of annual electrocutions could have been prevented by proper GFCI protection in and around the home, a staggering percentage. With the update of the technology, GFCIs aren’t just clunky plugs in your kitchen anymore, nowadays it’s just as common to see them in a breaker panel.
Dual Function breakers or “DFs” are specific breakers that function as both CAFIs and GFIs. This hard-working breaker cuts down on the bulk of material needed for locations that require both types of protection and is essential for locations that could make it hard or impossible to push the reset button of a GFI.
Locations and NEC Code articles
Arc Fault protection has its very own section (210.12) of the NEC under Branch Circuits that specifies the exact locations and conditions protection is needed. To summarize the article, Combination AF protection is required in any and all habitable spaces of dwelling facilities which include, but are not limited to, kitchens, bedrooms, hallways, living/dining rooms, and utility rooms. This applies not only to residential homes but also to dwelling areas in hotels/motels, dormitories, and nursing homes. Make sure to read the full article if you are unsure whether a circuit should be protected or not.
GFCI protection for personnel (the far more common use) can be found in the NEC under Branch Circuits in 210.8 and again in 210.13 for equipment over 1000A. To protect against electrical shock, ground fault protection devices are required in dwelling units wherever a receptacle circuit might be introduced to water including but not limited to kitchen countertops, within 6ft of sinks or showers, laundry rooms, garages/storage rooms below grade, and outdoor circuits. The same rules apply to non-dwelling units with some additions such as rooftops and service outlets.
Square D breakers
If you’re a fan of Electrician U videos, you might have watched the recent video on how to replace an electrical service, in which Schneider Electric was kind enough to supply us with its quality Square D equipment needed to get the job done. One exciting element of this service replacement is the use of a new Square D Plug-on Neutral design distribution panel, this design has a neutral bus that extends down the length of the panel for the breakers to be directly mounted to. Most anyone in the electrical field can testify what a relief it is to move away from the pigtail style neutral leads that have cluttered the interior of our panels for years. Here you get to see Dustin install all three types of these 20a Plug-on-Neutral breakers, CAFI, GFI, and DF. As Dustin’s house is an older one, many of his “home runs” are run in 12/3 Romex, which was a way to cut down on material costs by running two circuits that share one neutral. These “multiwire branch circuits” are allowed by article 210.4 of the NEC, providing the disconnecting means simultaneously disconnects all ungrounded conductors at the point that they originate. In Dustin’s case, this requires 2pole 20amp Arc Fault breakers that are not yet manufactured in the new Plug-on-Neutral design. This only means that the breakers he installs require the pigtail neutral lead of the older style CAFI breakers. Look for a link to Schneider’s line of Square D breakers down below.
Products used in Video
Square D Plug on Neutral 20a Breaker
Square D Ground Fault 20a Breaker