Technical Close call in the shop last night

Was doing some updating on our vintage travel trailer last night and was using several power tools on an extension cord. Obviously not at the same time. Closed up shop and went in for dinner. Came back out after church today to pick up tools and clean up a bit. Went to plug in the shop vac and no power.

This is what I found. I have about 6-8 outlets on this run. It’s a 20A breaker.
This is about midway in the run. Let oks like it started on the neutral side of the plug.
Could have been a lot worse.

 

I would assume your 20 amp breaker in the service Pannel saved the day by doing it's job.

 

Negative. It never tripped.

I got in touch with my nephew that is working for a local electric contractor and he asked what the rating was on my outlet. It was 15 amp. I think I am going to change the breaker to a 15Amp. Never really thought much about it.

Now I am paranoid.

 

Glad to hear you are not reporting on your shop fire. You dodged a bullet there. Why not change all your outlets to 20 amp outlets. A screw must have been loose to create that much heat and not trip a breaker. What was plugged into the outlet that burned?

 

Wall plugs should be on a 20 amp circuit, also the 20 amp plugs should have another “slot” in one side sticking out. That indicates a 20 amp plug. Check the wiring for the gauge and length of run.
What’s odd is that with that much cooked, the breaker didn’t trip.
FWIW, I don’t think a 20 amp socket is built to take more current than a 15 amp socket. I think it’s just an indicator with the slot.
But I didn’t take many classes on residential electric.
Maybe @Crazy Steve can shed some light.

Edit: Also take a look at the male end of your extension cord. Clean it up with a small wire brush. As they age they corrode a bit adding resistance.

 

Dang.
I’ve got GFCI ones on every circuit. Local code.
I also started just cutting off the main power when I’m not in it.

 

Whew! I had a near miss with the horn button sticking on my 49 Buick. It scared the crap out of me. The circuit isn't fused because GM didn't fuse it. Well, old horn buttons can short easily, so now mine is disabled and fused. Glad everything is ok. Put the right circuit breaker in there!

 

Depends on what size wire is in your shop. If it's 14-2, that's 15 amp, if it's 12-2 you're good for 20 amp. Running a 20 amp breaker with a 14 gauge wire can effectively turn your wire into a heating element. Like BJR said, it looks like your receptacle had a loose connection creating resistance. But if your breaker is a 20 amp, make sure you have 12 gauge wire.

 

Thanks guys. There wasn’t anything plugged into this particular outlet. It’s just midway in the run. I think I used 12 gauge when I wired the shop. I did it all myself, so if it’s wrong, it’s on me. I am thinking loose connection as well. Looks like I may get to check them all.

I think it was me taxing the system pretty hard last night. I had an extension cord drug up into the trailer and I had lights (LED) a circular saw and a sawzall up there. I did have a small fan but I would think the draw on it is pretty low. Downstream there is a small college fridge plugged in. I have moved it somewhere else just in case. It would probably have as much as the circular saw when the compressor kicks on.

 

I run about 30 calls a year at the firehouse related to outlets, and everyone of them are a loose screw on the receptacle. I don't know if it's from heat cycles on the copper related to draw on the outlet or not, but it makes you wanna kill the breaker and check all of your connections lol

 

Man,this could have been much worse. HRP

 

Resistance makes heat...
Glad the outlet is the only thing that burnt. Your lucky!

 

Wow. I had a neutral loosen up on a recep halfway in the run in my attached garage, it made there rest of the run dead but didn't heat up. I never use anything heavy in that garage, maybe a battery charger or the shop vac, but that's scary...

 

Glad it was not a catastrophe Root. Scary stuff!

 

what kind of wire? CCA? or real copper?

 

Looking at the receptacle, it had to happen some time in the past since you weren’t using it. Even a loose connection wouldn’t do that if nothing was plugged into it in my mind.
I think the bullet you dodged was from some time ago.

 

When I did my shop I was told not to Daisy Chain from plug to plug directly for connections. Wire nut the wires in the box with a pig tail going to the actual plug receptacles. I'm not sure if that's a code or opinion but that is how I did it 35 years ago. That said and your photo makes me think it might be a good idea to do some inspections. Can't hurt anything.

 

^ This. I pigtail all my receptacles and don't use them in a daisy chain type hookup. Much safer, as the buss on the receptacle isn't carrying the current load for the rest of the circuit.

 

Its all about the wire in the walls. 15A is 14awg white romex. 20A is 12awg yellow romex. Breaker amperage is based on the wire size. You can use 15A receptacles on 12awg wire/20A breaker. But not 20A anything on 14awg.

 

Excellent wake up For all of us...
Thanx for sharing...

 

I don't think it was from a previous episode @Budget36. It is basically wired in series and I had power until today. It happened after I went into the house last night. That's the part that scares me. I did notice the circular saw was struggling, but I thought I needed to swap out the blade.

I'm not sure I understand the whole pig tail deal. Can someone explain the advantage of doing this? Dumb it down for a novice.

I checked the wire. It is 12 gauge.

 

I suspect either a loose screw on the receptacle or a loose wire nut connector. Assuming 12-2 wire on the 20 amp circuit, nothing that you can plug into a 15 amp receptacle should tax anything assuming it's in good working order. I would consider putting a ground fault breaker on the circuit assuming that the installation was done before they were required.

 

I smell Federal Pacific breakers..

 

Back in the 70's and thereabouts there were a lot of buildings wired with aluminum wiring instead of copper. That aluminum wiring was notorious for developing loose connections, and the risk of an electrical fire is them was much higher. Those homes are still out there, and if you live in one it might not hurt to see if there is aluminum wiring in your walls. If there is, maybe pop open all the outlets and switches and check the connections.

A loose connection doesn't mean that there is enough current to trip the breaker. It just means that there is additional resistance, and when current flows through a resistance it generates heat.

He likely had the wiring "daisy chained" through the 6-8 outlets on the breaker that he mentioned. That means the wiring is run into one terminal on the outlet and out the other to the next outlet in line, so any outlet between the breaker and the outlet being used have current flowing through them. A loose connection in any of those could result in this near disaster.

 

Using wire nuts, wire the receptacle to the feeder wires using separate wires at the receptacle. The wire nuts continue the circuit through to the next receptacle, instead of the small buss/connection bar on the receptacle.
Hope that makes sense...

 

Ah, ok. I get it now.

 

current running thru a wire actually vibrates, causing connections to loosen up after years of service. Aluminum much more than copper. Its odd that it went with no load on it. In 2010 my shop burned up. 3 cars, tools, parts, building all gone. I have a disk with photos I'l post here some day. Electrical fire, started in the main panel. Never tripped the main breaker, and that building was fed off a panel in another building that did not trip either.
Good for you Root, not a disaster !

 

I'd freak out walking into the shop and getting hit with that distinct smell.

 

I’m with Budget 36. This problem was a while in the making. Like Lloyd said, probably from a loose screw! But the loose screw will not necessarily heat up due to resistance, it heats up due to arcing ! Loose screws become mini welders! That is where your heat came from, under load. It finally just arced enough to finally loose connection.
Still very dangerous!




Bones

 

To help understand the idea of pig tails, splice the hots together with a 6 to 8 inch pig tail for connecting to the receptacle. Do the same with the white, neutral, conductor. The only current the receptacle should carry is the amperage created by the device plugged into the receptacle. Looking at the burned up plug tells me the feed conductors were screwed into the plug and the load conductors were also. That is a very bad practice. All the current of the circuit is flowing through the small tabs the bridge the screws of the top and bottom outlets. I would highly recommend installing an Arc Fault Circuit Interrupter type breaker. If you had that type of protection, that burn out of the receptacle would not have happened. The Arc Fault breaker would have been tripping and you may have found the issue before any trouble occurred.