AFCI and GFCI, what's the differance?

[inspector_guy]

I firmly believe that the only stupid question is the one that you don't ask! So here I go. I understand that a GFCI is a 'ground-fault circuit interupter' and an AFCI is a 'arc-fault circuit interupter'. So what is the differance with these two devices? Is it what causes them to trip or how they are built? Is one better for certain areas than the other? By the way, when did GFCI's become code for kitchens, bathrooms, ect? I have inspected a few homes only two and three years old that had no GFCI's (breakers or receptacles)!
Tusen takk, Joe B.

 

[hillbilly]

Re: AFCI and GFCI, what's the differance?

Stupid question? Not for the average joe.
Have you ever done or been around a welder?
Arc fault is when you strike it without your helment down..... burned eyeballs.
Ground fault is when you touch the welding lead to your leg.....shocked like ......

 

[tom baker]

Re: AFCI and GFCI, what's the differance?

GFCI's first came into the NEC in the late 60's for swimming pool underwater lighting. Bathrooms followed in the early 1970's, kithens were not required to be GFCI's until mid 90's
An excellent book on how AFCI's and GFCI's work is Undercurrents and Overcurrents, by Earl Roberts. I got my copy from IAEI. This book also lists all the GFCI requirements by code cycle.
The definitions of AFCI and GFCI are in the 2002 NEC. Undercurrents and Overcurrents tell how they work.

[ August 16, 2003, 09:36 PM: Message edited by: tom baker ]

 

[inspector_guy]

Re: AFCI and GFCI, what's the differance?

Dad did all the welding on our farm when I was growing up. There wasn't anything he couldn't fix. Dad went to college for electricity in the late 50's but he couldn't afford the tuition so he returned to dairy farming. He kept his books and he wired up alot of our old buildings and buildings for our neighbors. I will try to get ahold of that book you mentioned. I don't like not knowing something. I appreciate the help.
Takk, Joe B.

 

[charlie b]

Re: AFCI and GFCI, what's the differance?

The following discussion does not represent the ?exact truth.? But it does have some truth in it, and it should help you understand the difference between the two devices.

The rules of electrical science require a complete path ? electrons that leave the source must return to the source. Every time an electron moves up the ?hot wire,? another electron is supposed to be retuning via the ?neutral.? (If anyone is familiar with the lack of precision in these terms, please ignore them.) If some don?t make it back via the neutral, then they had to have made their way back to the source by some other path. That other path is likely to include (1) Metal things that ought not to be energized, (2) Planet Earth, and (3) An unwary human. When current follows such a path, it is called a ground fault. A GFCI measures current on both legs. If it sees more current going out then going in, it trips, just on the odd chance that there might be a human in the current path.

An arc is the passage of current through air (not generally considered a good thing). A frayed wire in an extension cord is a frequent cause of such an arc. Sometimes the frayed tips of the wire mate, and can carry normal current. Sometimes they part, and interrupt current flow. An arc is drawn as the tips just barely separate, or just before they come once again into contact. If it is timed just right (or I should say, ?just wrong?), the ?on again off again? pattern can cause voltage to increase far above normal levels. The wire gets far hotter then normal, and can start a fire. An AFCI device is designed to trip when it recognizes the ?on again off again? pattern of current flow.

 

[bill brown]

Re: AFCI and GFCI, what's the differance?

I look at a GFI as a built in two Amprobe monitoring the current,when there are more them 5 milliamp different they trip.
I look at a AFI as a built in oscillosope mnitoring the voltage and trip the breaker when the voltage change due to a arc-fault

 

[Guest]

Re: AFCI and GFCI, what's the differance?

I started using GFI outlets and breakers for outdoor and bathroom receptacles in about 1975. Since then the code has changed to require them in garages, kitchens, basements, etc.

GFCI products against lethal shock. You will feel a buzz but you shouldn't die.

AFCI products against arc faults which are little fires waiting to turn into big fires.

 

[harley]

Re: AFCI and GFCI, what's the differance?

AFCI & GFCI both have a thermal and magnetic circuit. GFCI has a 5ma trip circuit. AFCI has a 30ma circuit like GF with ONE DIFFERENCE. You need a load applied to activate this circuit. Ex.
A grounded neutral (bare wire touching neutral screw on receptacle) GF will trip with no load AF needs some current draw before it will trip.
The Arc Fault portion trips on hot to neutral or hot to ground when the short circuit current @ the point of ARC is as low as 75 amps. The calibrated magnetic portion of the breaker cannot be this low because of nuisance trip. The lowest I have seen is about 150 amps and as high a 300 amps. How many times have you cut a hot circuit and not trip the breaker? One good reason is the short circuit current was well below the magnetic pickup of the breaker.
Voltage drops such as bad connections at receptacles (back stabs blind connections) not twisting wires with wire nuts (blind connections), long wire runs.