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I would like to know if Arc faults and circuit overlords are the only potential fire starters directly related electrical wiring failures or issues? I ask this assuming any device plugged in is not the issue (ie, appliance).

If this is the case does a afci (outlet or breaker) and standard breaker provide almost full protection? (I leave out gfci as I have not read that being related to fires but instead shock hazards)

I am including an updated list of electrical fire starters below based on the answers for benefit of other readers. These are direct underlying causes of ignition under the assumption appliance/device is operating correctly:

  1. Arcing
  2. High amperage overload
  3. Continuous amperage load over certain efficiency level of gauge wiring
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  • there is another .. the unforeseen circumstance
    – jsotola
    Commented Jan 15, 2021 at 23:29
  • Is there a problem you are trying to solve? Many homes have high resistance grounding electrodes it takes 6-8 ohms of resistance to ground to clear a direct fault to ground many homes have much higher levels even with multiple electrodes and I have seen a clamped hot conductor actually turn building materials to charcoal without tripping and to the arc fault it must have looked like a resistive load so no they are not fool proof.
    – Ed Beal
    Commented Jan 16, 2021 at 0:57
  • I installed two new double outlets. I used a pair of Klein wire strippers and they strip from 8awg to 18awg. I have 14awg wire but the Klein’s suck in the fact the printing on them is engraved on black blades so it could be hard to see. Well my last outlet I did when I attached pigtails to terminal one wire snapped so I must have nicked it . So now I’m second guessing myself thinking I could have done elsewhere on top of my lineman’s nicking wire as pretwisting. So if somehow a wire does break while in wall I’m hoping I understand what problems could arise. Afci just seems like nice safeguard.
    – Qiuzman
    Commented Jan 16, 2021 at 1:17
  • I just wanted to understand potential fire hazards in general to see if something unintentional like this would lead to a fire and protect against it.
    – Qiuzman
    Commented Jan 16, 2021 at 1:30

1 Answer 1

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A fire is just uncontrolled heating, right? When a thing starts burning what's really happening is a chemical reaction that produces heat, which causes more reaction, producing more heat..

So the question becomes: how can electric power deliver enough heat in a small space to get a chemical reaction (fire) started?

Arcs are a great way. An arc produces a lot of heat without a lot of current. That's why regular over-current circuit breakers weren't good enough and we added arc fault detection too. But arc fault detectors are tuned for certain parameters. They aren't fool-proof; an arc that falls outside the detection criteria would not cause an AFCI to trip. Consider the arcing that occurs in a brushed motor and doesn't trip an AFCI. If conditions were right similar arcs could occur in the wiring, would not be interrupted, and could start a fire.

That said: one can still get plenty of heat for starting a fire with neither arcs nor over-current. Cooking fires happen all the time as a result of electric power delivering fire-starting heat without exceeding over-current limits.

It isn't hard to imagine that a deteriorated connection, or even one that just never was great to begin with, could produce some heating somewhere in the electrical system. Maybe it will get hot (resistive heating) but never arc even once. This could start a fire without being detected by AFCI or over-current. Torque specifications for connectors are part of the solution to this problem.

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  • I want to see what other answers are provided but this is a great answer so far. So a cooking fires would be due to high amperage draw over a prolonged period of time?
    – Qiuzman
    Commented Jan 16, 2021 at 1:28
  • @IrishRedneck A cooking fire doesn't have to require high amperage. It just depends on the size of the food/cookware/stovetop/oven. The smaller they are, the less heat (less amperage) they require. Taken to an extreme: model rocket engines are ignited with power from a battery. One battery can ignite many engines before its power is consumed.
    – Greg Hill
    Commented Jan 16, 2021 at 1:51
  • so Is the underlying cause of fire in that case deteriorated wiring(ie, nicks in the wire or gouges in the conductor lowering awg)? If that’s the case can you elaborate on what would cause ignition or the chemical reaction equivalent to create fire? Based on your response we have 3 underlying fire causes for electrical. Any others you can think of? I believe this seems like a very open and vague question but from what I am gathering the underlying reasons for an actual electrical fire seem to reduce to a few causes.
    – Qiuzman
    Commented Jan 16, 2021 at 12:53

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