Through-the-wall A/C plug just caught fire

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Old 12-23-17, 08:27 PM
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Through-the-wall A/C plug just caught fire

I just got a good scare tonight.

I've got a GE through-the-wall air conditioner in a back office at my home that's been working great for about 15 years. A couple of nights ago I started smelling something strange when I ran the unit, but thought it might have something to do with the heating elements that hadn't been used since last winter.

Tonight, the smell became intense and when I glanced over at the unit I saw a small flame licking up the side of the wall where the unit is plugged into the 240 volt outlet. I immediately shut off the unit and swatted out the flame with my hand. After I turned off the breaker, I removed the outlet from the wall and saw the plastic junction box was partially melted and the Eagle/Leviton receptacle was burned to the point that the contacts had separated from the device.

The A/C plug and the wall outlet are both melted. The sobering thought is if the A/C unit had been running and I had stepped into another part of the house, we'd have a home fully involved in fire.

Any thoughts on what might have caused this?
 
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Old 12-23-17, 08:57 PM
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Welcome to the forums.

I see it all the time. It's caused by a worn out receptacle with a loose contact.
A loose contact creates tremendous heat especially with the load of a heater.
 
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Old 12-23-17, 09:08 PM
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Thanks Pete.

Pete, it's got two hot legs and a ground. The A/C has a heating element and requires 240v. I suspected it was a loose contact, but it seems so strange because it has never been disconnected. Maybe some corrosion over the years?
 
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Old 12-23-17, 09:32 PM
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The contacts weaken with age as well as the heating and cooling.
A plug for a high current appliance will usually get warm during use.
 
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Old 12-23-17, 09:37 PM
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Corrosion is a possibility.
It is very hard to determine what actually caused overheating once outlet is burnt all the way like that. It is also possible that the wire was not screwed tight enough in the first place.
Slightly loose connection will cause heat and expand wire and screw when the unit is turned on and cool the the unit is off. This cycles over the years can cause wire to become looser and eventually can cause failure like that.

That plug does not appear to be have a LCDI (Leakage Current Detection and Interruption). How old is the unit ?
I don't remember since when, but now LCDI is required on window and through the wall AC plugs. This would not have prevented fire you had, but just FYI.
 
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Old 12-23-17, 09:41 PM
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OP stated it's 15 years old.
 
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Old 12-23-17, 10:29 PM
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@lambition
LCDI Power cords were required for units made after August 2004
 
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Old 12-23-17, 11:23 PM
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Gremlins, I've seen this before.



As for the sobering thought, there is fire barrier putty that may slow down the flames from spreading for a couple hours or so.
 

Last edited by electrialdocius; 12-24-17 at 12:04 AM.
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Old 12-24-17, 10:44 AM
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Maybe an arc fault circuit breaker is the solution to prevent this from happening again?
 
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Old 12-24-17, 11:05 AM
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Yes, you can buy a combination 240/120 AFCI for many types of panels.

Your pictures show good reasons for other codes: namely, non-flammable outlet boxes, and boxes to be flush with the wall surface. That PVC plug will burn as you see, but even that is rated to be self-extinguishing after the current is stopped. The big issue, is how long will that current continue to run if left alone.
 
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Old 12-25-17, 06:39 AM
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Could the power cable [yellow romex] be aluminum, and worked loose? Just asking.
Sid
 
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Old 12-25-17, 08:10 AM
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Aluminum cable is too old to have a yellow sheath.
 
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Old 12-25-17, 10:22 AM
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Yeah I realized that the yellow romex wasn't part of the original problem it was part of an example. I meant the burned wiring.
Sorry for the error.
Sid
 
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Old 12-25-17, 10:50 AM
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We don't know what type of NM-b was used. We don't know it's yellow as that reference picture is not from this member. We do know it's copper as that can be seen in the first picture.
 
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