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-Home Inspectors
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Arc Fault Circuit Interrupters-
What You Should Know

    Arc Fault Circuit Interrupters (AFCIs) are devices that are
designed to detect and respond to dangerous electrical arcs
in home wiring. These devices are normally used to monitor
the arcing in branch wiring in the home...more specifically,
the branch wiring in bedrooms.

Arc Fault/ Ground Fault...What's the difference?

    The primary difference between an AFCI and a GFCI
(Ground Fault Circuit Interrupter) is what each are designed
to monitor and protect.
   A GFCI monitors the current flow
in electrical wiring and is designed to detect a GROUND
FAULT. This is where current leaks from a hot, or
ungrounded conductor, to a grounded object due to a
short-circuit. This situation can be deadly when a PERSON
becomes the electrical current's path to the ground. The
GFCI detects the fluctuation in current flow and trip the
circuit, thereby shutting off the flow of current. So, a GFCI
is designed to prevent PERSONAL injury due to a shock or
   An AFCI is designed to detect an arc or short-circuit AT
THE POINT of the arc, preventing fires and property damage.

How Does an AFCI Work?

    Electrical current flows in a "waveform", an undulating pattern of distinct peaks and valleys. An AFCI monitors this pattern for indications of an "arc"...a variation in the waveform that sometimes causes electrical current to jump from one location to another. We've all seen these arcs when we plug in, or unplug, an electrical device from a wall receptacle. A tiny spark jumps from the prong of the plug to the outlet, or vice versa.
   Part of the AFCI's job is to distinguish between these relatively harmless arcs and arcs that are serious enough to cause a short circuit, and ultimately a fire. AFCIs can respond to very minute changes in the electrical waveform, thereby protecting the branch circuit from dangerous arcing.

Where Do Arcs Form?

    Arcs can form in an electrical circuit in places where wiring insulation has been damaged, or in places where the wiring was improperly installed. An example of damage would be a wire that became pinched between two timbers as a home "settled" the insulation is slowly compressed and stripped away from the metal conductor, the current may arc to the wooden framing of the home and cause a fire. Another example would be a staple that pierced the insulation...the wire's protective coating is compromised and an arcing situation is created.

Other causes of arcing include:

- appliance cords that have become damaged by "pulling" or

- a liquid being poured or splashed onto an electrical    
  appliance or outlet/ receptacle

- a loose electrical connection in an outlet, light fixture, or   

- electrical cords that have been damaged by abrasion or  
  trapping, such as being run over by the vacuum cleaner or  
  trapped in a doorway

How Serious is Arcing?

   Pretty serious. Quoting an article on the NACHI website, approximately 21,000 homes were damaged in 2005 alone due to electrical arcing. Not to mention the human cost...500 lives were lost, and monetary damages were around $862 million. As I said, pretty serious. And the most worrisome part is, these arcs cannot be detected by traditional (non-AFCI) breakers.

Are AFCIs Now Required?

   In new construction, the NEC (National Electrical Code) calls for AFCIs to be installed to protect branch circuitry in residential bedrooms. The NEC has also recommended that this safeguard be carried require all branch circuitry serving family rooms, dens, sunrooms, living rooms, dining rooms, closets and hallways to be protected by AFCIs. This recommendation addresses all 120-volt, single phase, 15 and 20-amp branch circuits in a residential dwelling.

Nuisance Tripping of AFCIs

   One of the biggest complaints regarding AFCIs is their propensity for nuisance tripping. It seems that every time a tiny spark (arc) is created when connecting an electrical device, the AFCI shuts down power to the circuit. Not a very good situation, particularly if that circuit feeds a freezer or refrigerator...who wants spoiled food?

But there ARE some things that the installer (or contractor) can do to prevent nuisance tripping:

- check that all load wires, ground wires and neutral wires  
  are properly, and tightly, connected

- be sure that there are no shared neutral connections on a

- test the AFCI's operation with an AFCI testing device to
  identify sources of nuisance tripping

What Kinds of AFCIs are Available?

    There are several types of AFCIs on the market. These include:

- Outlet AFCIs...these are installed in a branch-circuit

- Branch (Feeder) AFCIs
...these are installed at the main
  distribution panel, similar to the way a GFCI breaker is  

- Cord Devices...these are a plug-in device which is
  connected to an electrical outlet

- the name implies, this is a combination
  of the OUTLET and BRANCH/FEEDER devices, and
  complies with the requirements of both

AFCI devices can be purchased at most home outlet stores and electrical supply stores. Professional installation is recommended so that your safety is ensured.


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