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AFCI Question


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Quote (Original):

One of my granddaughters slipped this penny behind the night light and the penny made contact with both prongs and the night light became a welder and cut the penny down to the size it is now

Tomorrow I will be installing arc fault breakers

Re: Why have arc fault circuits

« Reply #4 on: Today at 05:26:49 PM » Quote


Quote from: Steven Turetsky on Today at 06:39:56 AM

I wonder why the circuit breaker did not blow?

Will AFCI's address shorts, or just loose wiring/connections?

What type of panel is in the house? Would it be a Federal Pacific?

Quote from other:

This is how a welder works, there is no dead short, the arc faults do protect from this situation, or when pets or children chew through extension cords,

This from a arc fault fact sheet


Conventional circuit breakers only respond to overloads and short circuits; so they do not

protect against arcing conditions that produce erratic current flow. An AFCI is selective

so that normal arcs do not cause it to trip.

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By accident, I dropped a stainless steel thin wire across an outlet plug. The plug was in use by the lamp. The non-insulated wire touched the hot side of the exposed (lamp) plug connection and created a high current fault. Though the current flow was not across hot-to-neutral, but through the length of the wire (about 100'). The wire lite up like nichrome (heating) wire, or a heater, but did not trip the breaker. This caused a major fire by igniting the textile sofa next to the wall outlet. In seconds, flames were touching the ceiling.

This happended in a high-rise on Michigan Ave, Chicago in the 70s. I now have a good appreciation and reason for orienting the ground lug on the outlet toward the topside.

What was the wire for? It was a long wire short wave antenna that was hung out the window. It worked great until the great fire.

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Well, once again I've demonstrated how befuddled my understanding of electricity is. I could have sworn I'd popped breakers more than once when using cobbled together two prong extension cords and the hot and grounded conductors touched each other 'cuz I'd been a nimrod and hadn't yet taped up the splices.

Guess I got it wrong.



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If by chance, someone was to drop something conductive behind a plug, touching both prongs, would an regular breaker trip, or would you need an AFCI breaker for it to trip.

It depends. If the short had a high enough amp draw then the standard breaker would trip.

Lower amp draw and the standard breaker would not trip but then neither would the AFCI until there was an arcing in the circuit.

AFCI would yield better protection, but it is not fool proof. Even a combination AFCI/GFCI breaker will not detect all faults.

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Well, I don't know if it's a question, or comfirmation.

I was respondinding to a comment elsewhere, and lets say I was challanged. I knew I was right, just wanted to possibly get some verbage to post.

Thanks for asking though.

Ok, that makes sense now. I didn't understand the context and I was starting to get very confused.

With the penny, as Mike said, that's a dead short and it should trip the breaker. If it didn't trip the breaker, the breaker was faulty. If a dead short from a penny doesn't cause a breaker to trip, that's not a sign that you need an AFCI. The alleged super-duper powers of an AFCI are no better at protecting against dead shorts than any other properly operating breaker. The person who wrote, "This is how a welder works, there is no dead short. . . " is wrong. He doesn't know how a welder works or what a dead short is. He shouldn't be doing any electrical work before he learns some more about electricity.

If you (or a child or a dog) were to chew through an extension cord, you'd be zapped (or the child or the dog would). An AFCI or GFCI might protect you if your teeth were to create a ground fault, but neither an AFCI nor a GFCI would protect you if you were to create a line-to-neutral fault.

In KCInspections' example, there wasn't a "short", there was a "long". A long, thin, stainless steel wire is not a particularly good conductor. The circuit breaker sees this wire as if it were a light bulb or a heating element. An AFCI would have made no difference in the case that he cited. The wire would still have glowed hot and caught the furniture on fire.

AFCIs have an extremely narrow range of usefulness. They're not panaceas.

- Jim Katen, Oregon

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