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I had an outlet that had plastic socket covers inserted for child-proofing. Recently I tried to removed the top cover and noticed that was quite stuck. When I eventually forcing it out, I saw burn marks on (what was left of) the plastic prongs. After I removed the outlet, it seemed evident that the top receptacle probably arced sometime in the past and melted the socket cover, part of the outlet housing, and the insulation around the hot wire.

However, this outlet is on a circuit with an AFCI breaker. Shouldn't the AFCI breaker have prevented this? Or is something else happening? I have tried the test button on my AFCI breaker, and it switched to a middle position that required me to turn it the off position before I could turn it back on.

Left side of the outlet Right side of the outlet

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  • Depends... Was it a slow burn (over time) or did this 'blow up'???
    – Kyle B
    Nov 16, 2021 at 4:59
  • @KyleB I have no idea. The outlet was sitting unused with the socket cover in it for many months.
    – jamesdlin
    Nov 16, 2021 at 5:01
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    The only reason I would suggest this is that the AFCI is suspect, and I wouldn't do it routinely.... but you can also test the AFCI by plugging in a heater "almost" and jiggling it so the pins barely make contact, when you see intermittent blue-white flashes inside the receptacle, you're making arcs. Nov 16, 2021 at 5:15
  • it drew too much current for too long. could be a wire nick, a bit of terminal-clamped insulation, or even a crappy prong on a plug since removed: metal generally conducts heat as well as it does electricity.
    – dandavis
    Nov 16, 2021 at 9:28
  • Were the AFCI breakers upgrades, or were they original? If they were upgrades, it's possible the damage was here before the AFCI was installed and you've just now noticed. Though, TBH, that wouldn't explain the melted child safety plug... Uses recently calibrated Mk I eyeball that looks like #14 wire from here, is it a 15A or 20A breaker? If it's a 20A, something could have been drawing a full 20A over wire not rated for that much current.
    – FreeMan
    Nov 16, 2021 at 15:58

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Not all burns are caused by arcing.

For example, a toaster, hair dryer, space heater or any other device designed to produce large amounts of heat, if it malfunctions can easily cause a fire without any arcing at all!

The good news is that a lot of potential fires can be caught in time by monitoring for arcing. But not all. About the only technology that could do that would be if you put thermal fuses "everywhere". That makes sense in selected locations - for example, my oven (presumably most ovens) has a thermal fuse above the oven, behind the control panel, which is designed to fail if that area gets too hot. Given the nature of a large oven - 40A, produces lots of heat, etc., that extra protection (a dollar per oven) makes sense. But an extra dollar on every receptacle would fail any reasonably cost/benefit analysis.

Hard to say what happened in your case. Perhaps the receptacle parts got bent in a way that resulted in a high-resistance current flow - not a dead short (that would trip any breaker) and not arcing across a gap (which would trip the AFCI).

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