You are probably familiar with the Ground Fault Circuit Interrupter (GFCI), also called Ground Fault Interrupter (GFI), Residual-Current Device (RCD) and a few other names. While doing some electrical work for a family member, I discovered Arc Fault Circuit Interrupters (AFCIs) in the breaker box. Having a genuine Electrical Engineering degree (two, actually), I’d like to believe that I am reasonably up to date on basic house wiring. But somehow AFCIs had escaped my attention, even though they started appearing in the National Electric Code over 10 years ago.
A bit of searching on the internet revealed that these newfangled devices are intended to detect arc faults that are below the trip level of a normal circuit breaker. Think in terms of a frayed extension cord that arcs over, creating a fire hazard, but not exceeding the 15 ampere rating of a typical house circuit. As usual, the Wikipedia entry is a good place to start. AFCIs detect arcs by monitoring the current behavior throughout the 60 Hz cycle. There are characteristics in the waveform that indicate an arc condition exists, causing the AFCI to disconnect the circuit. This article goes into more technical detail if you are interested:
New Technology for Preventing Residential Electrical Fires: Arc-Fault Circuit Interrupters (AFCIs)
Just like GFIs, AFCIs are available for installation in the main breaker panel and for installation at the electrical outlet. The diagram below shows the block diagram of a typical single-phase AFCI. This is not your old school circuit breaker but a complex system that performs both arc and ground fault detection. As already mentioned, the arc detection is performed by sensing the current behavior. The ground fault detection senses the difference between the current leaving and returning to the device. If there is a significant mismatch between the two currents, a ground fault has occurred.
This post is just a quick introduction to AFCIs, with a USA perspective. Your local building codes are now or will soon be requiring AFCIs on new construction, so you’ll probably encounter them sooner or later. The National Electrical Manufacturers Association has a website with additional information: www.afcisafety.org.
73, Bob K0NR
Good intro. You might also mention the potential for ham radio causing AFCI trips. ARRL has worked on this. See http://www.arrl.org/gfci-and-afci-devices.
73 Martin AA6E
Martin, thanks for the link to the ARRL page. It sounds like there are more RFI problems with GFCIs, not so much with AFCIs.
I recently completed building a new home and moved into it in June of this year. We love our new “dream” home. It is almost perfect, except for the arc fault/ground fault circuit breakers we were forced to install to comply with the new regulations. I set up my new ham station, a TS-590s feeding a well-balanced, low SWR, multi-band antenna system. However, much to my enormous disappointment, whenever I get on the air, reguardless of the band, I consistently trip one or more of my Eaton arc fault/ground fault and AFCI circuit breakers. I have tripped as many as nine breakers at a time. I have talked several times to Joe Fellos at Eaton with no results so far. My electrician told me this morning that he has received numerous complaints from new home owners about the Eaton AFCI and arc fault/ground fault breakers. One lady tripped her breaker(s) every time she used her vacuum cleaner. Does anyone know if Eaton is the only brand having this problem? How about Square-D breakers; do they have this same problem? If anyone wishes, you can respond back to my email address: rmilliman@twc.com — K8HSY
Ron,
Take a look at the ARRL web page mentioned above. Some AFCIs are better than others. Apparently, some Eaton AFCIs have had problems with ham radio tripping them.
Bob K0NR
I just came across this eham.net forum discussion about nuisance tripping of AFCI due to ham radio transmissions. Lots of good info in the thread:
http://www.eham.net/ehamforum/smf/index.php/topic,96949.0.html