help me understand this scary electrical problem?

[Ken Platt]

Folks - I found a badly burnt receptacle, and I'm trying to understand how this happened so I can sleep tonight, and also so I know how to proceed in repairing it. I will readily confess to not being much of an electrical guy, but I read a lot and feel comfortable, usually, doing minor stuff like putting in receptacles, boxes, adding the occasional line from an existing one, and so forth.

This particular receptacle is somewhat hidden, above the microwave, covered by a kitchen cabinet (there is a hole cut in the cabinet back for access to the receptacle).It is on it's own circuit for running the microwave. It is a 20amp line. I'm not sure when I last laid eyes on the receptacle -we don't keep much in that cabinet, so it could be weeks.

Anyhow, today we saw obvious scorching of the upper portion of the receptacle. I probably shouldn't have, but I went ahead and tried running the microwave (hey, it was lunchtime!) which was plugged into the lower half of the receptacle and promptly saw the red glow at the neutral wire attachment screw.


Turned off microwave, (red glow fades), said some bad words, flipped off the breaker and pulled the outlet, and saw the area around the neutral (white) screw to the receptacle was very impressively charred. . The neutral wire was also of course burnt and broke right near the screw as I pulled the receptacle out from the box. It looked like the insulation was gone for a bit of the neutral, but with all the charring and so forth I can't tell whether it was stripped too far back, or the insulation had just been burnt off. The ground wire was attached to the outlet box (a metal box, of course) and not to the receptacle, which strikes me as odd. Is that ok?

And, why did the neutral screw start heating up as the receptacle draws current? I'm assuming somehow the wire was breaking so that the current had to bridge a narrow spot? How does this happen? Should the breaker have been flipping off?

I can replace the receptacle easily enough, but am wondering if there was something incorrect about the way it was wired that caused this. As far as I can recall, I've not touched that receptacle in the 18 years I've lived here, although the line was switched to a different breaker in the box (by a professional, not me) a year or so ago, if that might matter. The guy was putting in a 240v line for me, and the box was full, so he had to swap around a bit and put in some half-size breakers.

Thanks for all insight-

Ken

[Pat Barry]

I may be misunderstanding but if I read this correctly you have a loose connection to the neutral (white) wire and that loose connection is therefore a high resistance connection and will therefore heat excessively. Simply replacing the receptacle and properly securing the wires should be all that is needed. Remember, in AC 120V circuits, the neutral has to return all the current to ground so it does see all the current draw. Lets say your microwave draws 15A then 15A goes in the black and out the white (very simplistic of course because this is AC which flows both directions) so the white wire connection is equally important to powering your device as the black wire.

[Pat Barry]

One more thing - is this copper wire or aluminum. Aluminum was used for a while as a cost savings over copper but subsequently found to cause fires due to heating effects of the wires and connections.

[Rod Sheridan]

Pat correctly diagnosed the problem as a loose connection, and as he mentioned if the wire is aluminum you will need a receptacle that's rated for aluminum wire, or use a correct wire nut to attach a short length of copper wire, to pigtail to the recetacle.

Regards, Rod.

[Rich Engelhardt]

+1 to what Pat said.

Loose wires can cause arcing.
http://www.sawmillcreek.org/showthread.php?216551-Help-with-wire-nuts

Scroll on down to my name and check out the picture of what can happen w/a loose connection.

Also - when you do replace it - spend a buck or two and get one of the better receptacles instead of the $.49 specials.

[ray hampton]

the rec. ground screw are part of the tag on the end that are screw to the outlet box [metal box

[Ken Platt]

Thanks folks. I guess I somehow thought of the neutral as having less energy since the device has already taken out it's magic phlogiston. Or something like that, pretty silly of me since a long time ago I actually got an engineering degree, should be better at understanding this. Anyhow, the neutral actually broke a few mm away from the receptacle, so I don't think the actual connection was loose. Maybe one of those breaks that happens over time with movement of the wires?

Thanks for the heads up on the aluminum wires. They look like regular copper, though. The house is late 50's vintage, but the kitchen was clearly renovated sometime in the past few decades, and this receptacle had to have been put there just for the microwave, given it's 6 feet up over the stove. I'll double check the wires when I clip them back behind the damage, and they will then be so short that I'll be needing a pigtail anyhow.

Rich, very impressive picture, that's about what I'm looking at. And, yes, I too believe in getting better quality receptacles, although I'm always suspicious that it's the same ones in a different package. I usually get the one of the branded ones.

Still scary. Makes me want to go around the house and take off all the receptacle and switch covers.....

Ken

[Tom M King]

Replace the receptacle with a 20 amp one. It was just a bad connection, but everything about the 20 amp device is stouter than a 15 amp, which is probably what that one is.

[Phil Thien]

Agree with everything above.

Also, when you tighten the wire to the new receptacle, make it quite tight. If you've ever watched an electrician do this, once the screw is snug they death-grip the receptacle with one hand and give the screwdriver a good crank with the other. I suppose there is a fine line between overtight and not tight enough.

When I was younger I watched a friend that was a new homeowner replace receptacles and the first one where I watched carefully I realized he wasn't getting the screws tight enough. When he put the receptacle into the box there was enough torque added by the wire that the screw turned. So we had to open the new ones up again and crank them down better.

His problem was using a screwdriver with a blade that was too small. Use a blade or bit that gets a good purchase on the screw.

Also, use screws and not the receptacles with the side clamping. The side clamping is great for stranded conductors (if that is what you have). But for solid wire, I think a wrap around screw lug is more secure.

Also, if there is ever truly doubt about your power, kill the suspect breaker(s) before sleeping.

[Bruce Page]

Replace the receptacle with a 20 amp one. It was just a bad connection, but everything about the 20 amp device is stouter than a 15 amp, which is probably what that one is.

Not a good idea, IMO. Better to purchase a quality 15amp receptacle. Someone down the road might plug in a 20amp device thinking it's a 20amp circuit and overheat the wiring.

[Patrick McCarthy]

Not a good idea, IMO. Better to purchase a quality 15amp receptacle. Someone down the road might plug in a 20amp device thinking it's a 20amp circuit and overheat the wiring.

Although he said it is a 20 amp circuit dedicated to the microwave. Ken, is the circuit wiring 12 gauge?

[Chris Padilla]

Not a good idea, IMO. Better to purchase a quality 15amp receptacle. Someone down the road might plug in a 20amp device thinking it's a 20amp circuit and overheat the wiring.

Well that is where the breaker should kick in and protect the in-wall wiring, correct? He did state the wiring was 20 A so I'm assuming #12 wire.

[Phil Thien]

Well that is where the breaker should kick in and protect the in-wall wiring, correct? He did state the wiring was 20 A so I'm assuming #12 wire.

I think it is moot anyhow, I don't think there is really much of any difference between the innards of a 15A receptacle, and a 20A receptacle.

[Bruce Page]

Well that is where the breaker should kick in and protect the in-wall wiring, correct? He did state the wiring was 20 A so I'm assuming #12 wire.
Ah, I missed that. :o I thought it was a 15amp circuit.
https://www.youtube.com/watch?v=V3FnpaWQJO0 :)

[Chris Padilla]

Ah, I missed that. :o I thought it was a 15amp circuit.
https://www.youtube.com/watch?v=V3FnpaWQJO0 :)

"Nevermind!" Someone once told me: "Reading is fundamental!" hahaha! Have a GREAT weekend Bruce...maybe you started early?! :p

[Bruce Page]

"Nevermind!" Someone once told me: "Reading is fundamental!" hahaha! Have a GREAT weekend Bruce...maybe you started early?! :p
Not yet but soon!

[Tom Stenzel]

The advice you've gotten above is good. One other possibility is that when the wire was stripped it had been deeply gouged. The heating and burning would have then started there. Make sure you don't nick the wire when you strip it.

Trim the all the burned section of wire off and you should be OK.

-Tom

[Mike Cutler]

Ken

There is a difference between the receptacles that cost 99 cents and the ones that cost 3 to 5 bucks. A quality Pass and Seymor duplex receptacle will last a lifetime.
A Microwave is a pretty powerful household appliances, probably the more powerful of all the "common" appliances that plug into a 120 circuit. The little ones are running a thousand watts and the bigger ones will easily push 1500 watts, and maybe a little more.

As a PS;
Consider swapping out that receptacle with GFCI receptacle. One will cost you about $15-$20 dollars, but the protection it affords is worth it. Also visually check for any gaps between the box, and the cabinet and wall. There should be no gaps. The front of the box should be flush with the inside of the cabinet backplane. If there are any gaps visible there are " box extenders" to enclose the "arc gap". They're at Home Depot and are color coded for the spacing required. They're only a dollar or so if you need one. It also sounds as if this microwave is a permanent, cabinet undermount unit, and as such it really should have protection.

[Myk Rian]

I replaced every outlet in the house because they were of the type where you just push the wire in, and that's that.
ONLY use the type, where there are honest to goodness screws to tighten.

[Ole Anderson]

As noted by Tom, it is not unusual when stripping a wire to nick the copper pretty substantially, and when jamming the wire (a 12 ga) into the receptacle to either snap it at the nick or to partially break it, which is what I suspect happened in your case. Using the 14 ga strip grooves on a 12 ga wire or using an improperly adjusted cheap v-notch stripper will do it.

Personal preference, but I prefer the side grip, screw tightened receptacles, contrary to Phil. Easier to wire and much easier to rewire. And many of them allow two wires per screw which eliminates a lot of wire nuts in crowded boxes. I do stay away from the back stabbers, though. However, the back stabber design is similar to the new stab type wire connectors, which are quite nice. But then we could rehash the argument for pre-twisting the wire before screwing on the wire nut too.

[Phil Thien]

Personal preference, but I prefer the side grip, screw tightened receptacles, contrary to Phil.

Not trying to be argumentative, but I suggest anyone considering the side-clamping receptacles try clamping a wire and then wiggle the wire around. My experience is that the clamp will loosen up.

[Duane Meadows]

Just one other caution, check the plug on the microwave... if it's burned or discolored you need to replace the plug/cord on the microwave also!

[Tom M King]

Not a good idea, IMO. Better to purchase a quality 15amp receptacle. Someone down the road might plug in a 20amp device thinking it's a 20amp circuit and overheat the wiring.
He said it was a 20 amp circuit. Most houses are fitted with 15 amp receptacles even on 20 amp circuits.

[Tom M King]

I think it is moot anyhow, I don't think there is really much of any difference between the innards of a 15A receptacle, and a 20A receptacle.
There is a small amount of difference in beef in the metal parts. Even a 20 amp device from a big box store can hold more torque on the screws than the 15 amp ones. The worst offenders in failing devices were ones from the '70s and 80s that just had a little spring to hold contact with the wire pushed into the back.

I ground a slot in a pair of needle nose pliers that makes a perfect loop to fit on screws for devices that allow post mount-saves a lot of fiddling.

When wiring a receptacle, I fit the ground first with the post up, then the white wires, and one half turn to get to the black side allows it to go right in the box. Doesn't make a whole lot of difference in time saved for one device, but when doing a whole house, it's definitely more efficient.

Screwdrivers in the Electric box are only used for screws. It's hard to get a good bite for good torque with one that's been used for scraping concrete.

[Brian Elfert]

I like to use the receptacles that are back wire, but with screws instead of the style with springs. They cost a lot more than the cheap residential receptacles, but they are better quality. Some people don't like them because it is hard to push the plug in. They are tight so they don't wear out and get loose over time. The problem with looping the wire around a screw is it is hard to make a proper loop and get it squarely under the screw. I admit I am very bad at it myself.

[Tom M King]

I agree also about the back wire ones that are tightened with a screw. All the 20 amp ones I've had my hands on lately were like that, and plenty substantial. I also agree about the loop. It's pretty hard to make it a really good fit freehand repeatably. That's why I took a little while to grind a correct slot in a pair of needle nose pliers that makes a loop perfectly, and quickly and easily.

[Don Huffer]

Not a good idea, IMO. Better to purchase a quality 15amp receptacle. Someone down the road might plug in a 20amp device thinking it's a 20amp circuit and overheat the wiring.

That's what I thought.

Don

[Phil Thien]

There is a small amount of difference in beef in the metal parts. Even a 20 amp device from a big box store can hold more torque on the screws than the 15 amp ones. The worst offenders in failing devices were ones from the '70s and 80s that just had a little spring to hold contact with the wire pushed into the back.

Probably not actually because 15A receptacles are required to handle a 20A feed-through, as multiple 15A receptacles are allowed on a 20A circuit.


I ground a slot in a pair of needle nose pliers that makes a perfect loop to fit on screws for devices that allow post mount-saves a lot of fiddling.

When wiring a receptacle, I fit the ground first with the post up, then the white wires, and one half turn to get to the black side allows it to go right in the box. Doesn't make a whole lot of difference in time saved for one device, but when doing a whole house, it's definitely more efficient.

Screwdrivers in the Electric box are only used for screws. It's hard to get a good bite for good torque with one that's been used for scraping concrete.

I never found it necessary to make perfect loops as the screws on decent receptacles are underground. I make an okay loop and then tightening the screw itself will take care of the rest. This is especially true with 14-gauge wire, 12-gauge often requires a snug/loosen/snug, but I get the same result.

[Phil Thien]

I like to use the receptacles that are back wire, but with screws instead of the style with springs. They cost a lot more than the cheap residential receptacles, but they are better quality. Some people don't like them because it is hard to push the plug in. They are tight so they don't wear out and get loose over time. The problem with looping the wire around a screw is it is hard to make a proper loop and get it squarely under the screw. I admit I am very bad at it myself.

Well one of these days wire one up and then wiggle the wire until it comes out of the clamps. Now try that with a wire under a screw and the wire will break before the screw lets it go.

Here is a quote from the Mike Holt electrical forum from a senior member talking about what I've observed. Clearly he is still using them, I'm not saying they are the root of evil, I'm just saying they will let go on you:



I've used the Leviton Pro-Grade receptacles exclusively for several years. They are difficult to side-wire & I've only used that technique when I had to cram a receptacle into a very shallow 1" deep box. The back wire connector is generally quite secure although on a few occasions I have tightened the screws, started to push the wires into the box, felt them slip loose and had to retighten the screws. I now install them with a cordless screwdriver with a straight bit and manually twist the screw down hard. I then wiggle & pull on the wires before pushing them into the box. Have never had a call back or failure. I tried to take one apart once to see how they were constructed and gave up after beating on it with a hammer for a few minutes!

[Ken Platt]

This has continued to be a very interesting discussion, folks, thanks for all the contributions.

For those who were wondering about the wire gauge, I'm not certain. I'll have to round up some samples tomorrow and compare. I can't tell by just looking.

I started to try to make the repair tonight, and wasn't able to strip the insulation off the wire (even after cutting off the burnt part, of course) - I'm guessing the heat fused it on, even a few inches back. And, I can't cut much farther back because I don't have much wire length in the box to play with. If anyone has any suggestions on this, I'd love to have them. As it is, all I can think to try is scraping off the insulation with a blade, although I'm not wild about this as it might damage the wire.

Ken

[Ole Anderson]

I started to try to make the repair tonight, and wasn't able to strip the insulation off the wire (even after cutting off the burnt part, of course) - I'm guessing the heat fused it on, even a few inches back. And, I can't cut much farther back because I don't have much wire length in the box to play with. If anyone has any suggestions on this, I'd love to have them. As it is, all I can think to try is scraping off the insulation with a blade, although I'm not wild about this as it might damage the wire.

Ken
The old axiom, "nothing is ever easy" seems particularly true for having to get into an old electrical box when the previous installer didn't leave enough wire. One suggestion is to use a stripper that will reach into the box, a v-notch tool typically does that. Now you have a wire that may be too short to easily use a wire nut, but a stab style wire connector doesn't require as much room to install. You might first try loosing the cable clamp in the box and see if you can pull more into the box.

https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcRqQ1036t0mr9N2vww-awe_r1ATMHhW5JFY0MqeJrBD8CJT8P2vrg

[Chuck Wintle]

This has continued to be a very interesting discussion, folks, thanks for all the contributions.

For those who were wondering about the wire gauge, I'm not certain. I'll have to round up some samples tomorrow and compare. I can't tell by just looking.

I started to try to make the repair tonight, and wasn't able to strip the insulation off the wire (even after cutting off the burnt part, of course) - I'm guessing the heat fused it on, even a few inches back. And, I can't cut much farther back because I don't have much wire length in the box to play with. If anyone has any suggestions on this, I'd love to have them. As it is, all I can think to try is scraping off the insulation with a blade, although I'm not wild about this as it might damage the wire.

Ken
Ken,
If it was me I would run a new length of wire back to the electrical panel. As you stated the wire near the plug overheated and the insulation is damaged and it unusable.

[Lee Schierer]

Even though it is a 20 amp breaker, check the wire size to insure it is #12 wire. I've seen two houses now where there were 20 amp breakers in the box, but some clown used #14 wire in all or part of the circuit to save a few pennies when they added a recptacle.

[Ken Platt]

Checked against some new, yes, it is 12 gauge. Got the repair completed, thanks all.