220v receptacle leg burned - why?

[Chris Barnett]

Had problem that dryer would not heat (ok, not in the workshop but next door... but if I loose the dryer...I loose the shop...and the house, so its shop related :o). Dryer drum would turn but no heat. The breaker had tripped a few days before but could not find a problem after removing back panel and inspecting, so I reset breaker. Did not unplug until yesterday when the dryer would not heat, although the dryer would turn and dry on air only.

I unplugged the dryer to move for another internal inspection yesterday and noticed plug burned as in picture. There was no discoloration on other end connected to dryer. The plug box in the wall is a mess, the black wire in receptacle was vaproized, and the wire end projecting out other side was a round ball from the heat. Several inches of wire connecting to the terminal were missing, then several inches of charred insulation on remaining wire exists, then remaining few inches of wire with pliable insulation exist inside the box, but too little to make a new connection to a new receptacle.

The photo shows a holiday in white insulation on the ground wire and indicates a possible arc to ground. Seems though for an arc to ground to occur would require holiday on both the black hot leg and the same on the ground (as seen in photo) and these places to align such that metal to metal contact could occcur.

I cannot figure out (other than matching holidays) what happened, which I need to know before repair or replacing and turning breaker on. This could have caused a fire. The receptacle got so hot that it crumbles around the shorted leg connection.

Would a wire loose in the terminal cause this to occur? Or could a fault in the encapsulated plug be the cause? I think the plug would show more heat damage than is seen. Inspection of the accessible portion of the 220v line approximately 6 feet from the receptacle shows no anomolies. I do not think the wire was loose in the electrical box since the end projecting from the terminal was heated to a round ball.

I noticed that inside the electrical box housing the receptacle, the paper packing between the ground and the conductors where the outside cable covering terminates is not burned.

Need to know what caused this, simply by looking at the photos. All was well for 35 years and would like an extension on those years :).

Second question: Since wire is inside block behind drywall, can a new wire be spliced to the old via wire nuts (above the wall where wire enters tghe block wall) for a new wire end to the new receptacle or is a new wire required from the breaker to the receptacle?

[Steven DeMars]

Remove everything.

First of all for safety sake do not put that large of a receptacle back into that "small" metal box. It is very hard to place all that in a small box without potential problems. I know, electricians do it everyday, & that is the key, they do it everyday. It looks to me that a ground out to the box may have been your problem to start with.

I would replace the box with a properly sized heavy duty plastic box. Next I would go with a quality receptacle. I would go above with another small box to serve as a "junction box to make a splice. Wire nut and tape with Scotch #33. Any splice must be contained in a "box". Do not simply cut splice and wire nut in the wall.

You said this dryer out ran the shop. Not sure what you met. I will caution you that the type of plug / receptacle you are using is NOT designed to be plugged and un-plugged. In order for that receptacle to function as it is designed it requires a lot of effort to plug into it & to remove the plug from it. It is a Bakelite type of material and you will crack it over time.

I would definitely change out that breaker also. You might want to check your dryer exhaust outlet, it may be leaking, which would add moisture to your wall and cook your receptacle.

Steve

[David G Baker]

I agree with Steven, good advice.

[Dan Hintz]

No arguments here... to me, it looks like the outlet was slowly giving up the ghost, and arcing within the outlet was the cause of the burn.

[Mitchell Andrus]

Any splice must be contained in a "box". Do not simply cut splice and wire nut in the wall.



I have seen a splice kit for this. I don't know if it's 'code' or not but it wasn't just a wire nut and tape. As I understand it, the junction box has to be accessible.

Anyone see this box-less fix?
.

[Rob Russell]

I would suspect that the original connections to the plug started to loosen up over time. That would cause heat build up which would cause the conductor insulation to get brittle and fail and then you could get that arcing.

As previously noted, I'd replace the single gang box with an "old work" 2-gang plastic box. That box will be large enough so you can wire nut on leads to connect from your supply cable to the receptacle without worrying about a separate "splice box".

[Callan Campbell]

Usually the root cause is that the female tabs or contacts inside the outlet/recept. get loose, then the wire, contacts and male plug terminal get hot from the resistance, melting whatever gives first. You're lucky you didn't have a fire from this, and that the breaker was trying to do its job with what was probably close to the amp rating of the circuit and wires being pulled through it. It's a mess, for sure, but once you get all the bad wiring out, switch out and update the box, outlet, and plug to the appliance as needed, you'll sleep better at night.
:o

[Chris Barnett]

Regarding the shop, was simply justifying posting a problem about a clothes dryer and not a shop wiring problem, saying that if I loose the laundry due to a fire, I loose the shop too..i.e. thus shop related.

Looking at the receptacle purchased for a replacement, I am not enthused with the seemingly light duty even though the plug is removed only if the dryer needs servicing or needs to be replaced; perhaps I need to go to a electrical supply and see what they have, in addition to a plastic box and new breaker. The space behind the drywall is dry as a bone so exhaust leakage is not indicated. The loosening of the terminal screw due to thermal cycling might be the cause of higher temperatures and arcing, but I should expect the torque to be sufficiently high to prevent this. Will look for torque values on the replacement socket.

And thanks for all the information and comments.
Chris

[Dave Houseal]

I would suspect that the original connections to the plug started to loosen up over time. That would cause heat build up which would cause the conductor insulation to get brittle and fail and then you could get that arcing.


I've seen this happen before. Thank God for circuit breakers!

[David Cefai]

+1 on a loose connection being the cause. Over here we have 220V single phase 50Hz domestic power. I've had the odd plug heat up and char slightly (not as badly as the one pictured) and recently had a similar problem where the mains supply enters the house. The problem has always been due to a loosened connection.

What helps is:

1. When wiring a plug, wait a few minutes and then retighten the screws.

2. "Tin" the wire with solder.

Hope this helps.

[Rick Potter]

Is that wire aluminum? It is about the right age, and there were a lot of problems caused by the aluminum wire either loosening up, or not compatable with the plug. They later developed plugs to take either wire.

Lotsa fires caused by this. Especially in mobile homes, where they used a lot of it. Many homes had copper throughout except for the large wires to the dryer or stove, which were aluminum.

Rick Potter

[Tom Hammond]

Any splice must be contained in a "box". Do not simply cut splice and wire nut in the wall.

Splices must indeed be in boxes, but they also must be accessible to be in code. You cannot enclose a junction box behind drywall.

[Anthony Diodati]

I know this is an older thread, but reading this I would like to replace mine (outlet)
What is a good brand to get? This is a surface mount type outlet.
It is the 3 prong type, I will not be up grading to 4 prong at this time.
TY
Tony

[Anthony Diodati]

Ended up with this one From ACE for about $6.00
175488
http://www.acehardwareoutlet.com/productdetails.aspx?sku=3201449&source=GoogleBase