Monday, August 07, 2006

Arc Fault Circuit Interrupters

A significant change in the National Electrical Code (NEC) took place in January, 2002 that will enhance the safety of your home. The NEC is a set of standards developed by the National Fire Protection Association (NFPA) adopted by most regulatory agencies. The Occupational Safety & Health Administration (OSHA) often uses the NEC standards to set their requirements for commercial and industrial establishments. It is likely that your local government regulatory agency such as a state or city electrical inspector also uses the NEC to set the standard for homes or businesses within their jurisdiction.

So what changed? The 1999 edition of the NEC set a deadline of January, 2002 for requiring Arc Fault Circuit Interrupters (AFCI) for receptacles in bedrooms. Most people want to know what an AFCI does compared to a Ground Fault Circuit Interrupter (GFCI). Well, hopefully you are already familiar with the GFCI since it has been required for various applications since 1971. The original requirement for GFCIs included outdoor locations and swimming pool areas. But today it has spread to include areas around swimming pools, hot tubs, spas, outdoor locations, bathrooms, garages, boat houses, kitchens, unfinished basements, crawl spaces, and wet bars. Of course there are some exceptions and you should probably consult a licensed electrician to understand the requirements and how they apply to your home.

So, let’s review the GFCI before we discuss the AFCI. Electricity always needs a complete path from its source to the destination and back to the source. That loop can either occur through various things including the ground and even your body. The electrical receptacle in the wall has at least two slots and hopefully at least three counting the ground. One slot passes electricity out of the outlet. The second slot allows the electricity to make the return path. The third hole or slot provides an alternate path we call a ground. The ground is intended to be more attractive for the electricity than your body if a primary path fails. But, let’s look at the two primary paths. A GFCI looks at the amount of electricity passing out one primary path and returning on the other primary path. If those two values do not match it must assume the difference is going where it should not go which might be your body. After enough difference is seen the GFCI will turn off the circuit. That amount is very small, approximately 5 milliamperes. But it is just below the threshold that will start causing damage to your body.

The AFCI is designed to protect you from arc faults, something quite different than a GFCI. Arc faults occur when the electricity is arcing randomly from a problem with the wiring. This arc is very hot but does not pull enough electricity to immediately signal a problem for the circuit breaker. The arc looks like somebody is welding and is often accompanied by the smell of ozone. An arc can reach thousands of degrees and easily start a fire without being recognized. In fact, the NFPA estimates 40,000 fires result each year from arcing faults. An AFCI has intelligence to recognize the random patterns of electricity used by an arcing fault and will open the electrical path under those conditions.
Today you can purchase an AFCI to fit inside your circuit breaker panel similar to the GFCIs designed to fit in your circuit breaker panels. In fact, other than function, they look similar. You will soon be able to purchase a combination GFCI / AFCI circuit breaker if they are not already available. Look for more changes in the code to require the AFCI in other applications as the technology develops. Hopefully you will never require the protection of an AFCI or GFCI, but isn’t it nice to know it is there watching out for you?