Arc Fault Circuit Interrupters

Arc Fault Circuit Interrupters Protect People from House Fires Caused By Electrical Arcing

By Mark J. Donovan

Arc fault circuit interrupters (AFCI) are different from standard circuit breakers. Arc fault circuit interrupters are specifically designed to turn off power to a circuit when they sense a non-working electrical arc. A standard circuit breaker, on the other hand, is meant to sense an overload circuit or a short circuit. The main purpose of arc fault circuit interrupters is to prevent fires due to arcing. Tens of thousands of fires are started in homes each year due to electrical wiring problems, and much of the time the fires start due to electrical arcing.

Arc fault circuit interrupters are similar to ground fault circuit interrupters (GFCIs) and residual current devices (RCDs) due to the fact that they each have a test button to confirm the interrupter is working properly.

However, unlike arc fault circuit interrupters, GFCIs and RCDs work to protect people from life threatening shocks.

An arc fault circuit interrupter is specifically designed to know the difference between non-working arcs and common working arcs. A non working arc could possibly occur via a broken wire in an appliance or lamp cord. Common working arcs, on the other hand, occur when throwing a light switch, or inserting or pulling a plug from an electrical outlet. They also occur in certain appliances with motors, such as a vacuum cleaner, due to the arcing of the metal brushes inside the motor.

National Electrical Code (NEC) laws now require that on all new construction the dwelling units within the home must have installed arc fault circuit interrupters on 120 volt, single phase, 15 and 20 amp branch circuits. Dwelling units include bedrooms, living rooms, family rooms, dining rooms, dens, libraries, sunrooms, closets, hallways, parlors or equivalent home living spaces.

An AFCI continuously monitors a circuit checking for and detecting erratic and reduced current loads on it. When an arc fault circuit interrupter does detect a non-working arcing condition it trips and the power to the branch circuit is shut off, thus preventing the risk of fire.

AFCI’s are specifically designed to prevent normal arc conditions from tripping it and shutting off power to the branch circuit that it is installed on.

Though arc fault circuit interrupters are in theory an excellent protective device, many homeowners and electricians have been frustrated with them and have argued they are not ready for prime time deployment. Though AFCIs are supposed to only detect non-working electrical arcs, they unfortunately do trigger occasionally on standard working arcs. For example, certain appliances or normal events often trip them. This leads to frustrated homeowners calling back electricians to figure out what electrical device is causing the AFCI to trip and in many cases replacing the AFCI altogether.

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