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Title: Overheated Edison Plug
Post by: Mike Sokol on February 13, 2017, 10:48:07 am
Just found this overheated Edison plug in our extension cord pack over the weekend. What got us looking at the plug was the fact it showed a swapped Hot-Neutral while testing the stage power for a gig. Further exam showed that it was badly overheated sometime in the past. Note that the "white" wire insulation is now brown, and the plastic separator on the plug has been melted into something that looks like lava-glass.
Title: Re: Overheated Edison Plug
Post by: John Rutirasiri on February 13, 2017, 10:56:14 am
I no longer let anyone borrow my extension cords because people were plugging my 15A cord into 30A RV adapters.  They then put a T on my extension cord and ran more extension cords off my cord.  For all I know they were pulling close to 30 amps through my cord.

John R.



Title: Re: Overheated Edison Plug
Post by: John Roberts {JR} on February 13, 2017, 11:03:59 am
I've experienced a warm plug in a decades old Edison outlet from elevated contact resistance. The replacement outlet ran cool.  8)

More recently I replaced the old Edison outlet in my laundry room (with GFCI) that was actually dropping power to one plug position. The washing machine in the other outlet position never dropped power, but the dishwasher would annoyingly hang up mid cycle and not finish, every time power to it was momentarily interrupted. Since replacing the outlet with new it has been 100% solid.

JR   

PS: Speaking of extension cords, I shared my old story about the extension cord I borrowed from one neighbor to run my sump pump in a mud hole in my yard that had ground and line swapped... not a good thing for using electricity in a hole full of water.  :o

PPS: A different neighbor has an extension cord with the green ground wire just hanging out unconnected at one end. When I pointed that out to my neighbor he was completely unconcerned (he is 20 years older than me). He was using it to cut some wood in his car port and I would have stopped him but the saw was 2-wire line cord so double insulated. I plan to sneak over there when he isn't looking and repair it (maybe a project for today).

[follow-up] today repaired my neighbors extension cord that had the green ground wire hanging out one end. After taking the end off I noticed a break in the insulation on the black (hot ) lead, that could have shorted to neutral if line cord was twisted. :o. I re-stripped and kept the leads shorter. Should be good for his lifetime, probably mine too. [/follow-up]
Title: Re: Overheated Edison Plug
Post by: Tim McCulloch on February 13, 2017, 12:23:05 pm
Just found this overheated Edison plug in our extension cord pack over the weekend. What got us looking at the plug was the fact it showed a swapped Hot-Neutral while testing the stage power for a gig. Further exam showed that it was badly overheated sometime in the past. Note that the "white" wire insulation is now brown, and the plastic separator on the plug has been melted into something that looks like lava-glass.

I'll try to find the pic I have from Sesame Street Live laundry.  Their dryer had an L14-20 melt down.  Their show electrician apparently didn't see a problem replacing a 30 amp connector with a smaller connector.  I was the house electrician who went running with a fire extinguisher when a touring person got on intercom and said "our dryer is smoking."  It wasn't the dryer itself, but the connection next to it.

The heat deformed both the male and female connectors and it took a hammer to separate them.  When we did, it was also evident that the hot or neutral screw (can't remember which) wasn't fully tightened.  The show electrician had replaced the connectors a week before and he never went back to check his work.

VEE Corp - if we don't kill you in the first 3 years, we'll give you a raise....
Title: Re: Overheated Edison Plug
Post by: TJ (Tom) Cornish on February 13, 2017, 04:14:40 pm
Just found this overheated Edison plug in our extension cord pack over the weekend. What got us looking at the plug was the fact it showed a swapped Hot-Neutral while testing the stage power for a gig. Further exam showed that it was badly overheated sometime in the past. Note that the "white" wire insulation is now brown, and the plastic separator on the plug has been melted into something that looks like lava-glass.
Even a properly torqued connector can loosen over time.  I disassemble all my SO cords and re-torque every other year or so.  I always find a couple that need a 1/4 turn on a screw.  It's a nice winter project, and in Minnesota I have a nice amount of winter to spread the work over; though once again the East Coast has gotten way more snow than we have.
Title: Re: Overheated Edison Plug
Post by: Mike Sokol on February 13, 2017, 04:25:01 pm
Even a properly torqued connector can loosen over time.  I disassemble all my SO cords and re-torque every other year or so.  I always find a couple that need a 1/4 turn on a screw.  It's a nice winter project, and in Minnesota I have a nice amount of winter to spread the work over; though once again the East Coast has gotten way more snow than we have.

It's hard to tell if the screw was loose or not since it's completely covered over with melted plastic due to overheating. Hey, I guess it's locked in now for sure... However, the black wire (which is actually the neutral connection in this mis-wired plug) shows no sign of overheating. So the most plausible explanation is a loose screw on the white wire (actually the line connection) caused it to overheat and meltdown everything. Time to do maintenance on all of our extension cords and test them.

Title: Re: Overheated Edison Plug
Post by: Ike Zimbel on February 13, 2017, 09:15:18 pm
It's hard to tell if the screw was loose or not since it's completely covered over with melted plastic due to overheating. Hey, I guess it's locked in now for sure... However, the black wire (which is actually the neutral connection is this mis-wired plug) shows no sign of overheating. So the most plausible explanation is a loose screw on the white wire (actually the line connection) caused it to overheat and meltdown everything. Time to do maintenance on all of our extension cords and test them.
A good trick that I learned somewhere over the years is to give the connector a shake before you plug it in (or better yet, before you put it in a case and send it to a show). If there are loose screws inside, you will usually hear a little rattle. I've found lots of loose connections that way.
On a sort of related note: Years ago (1983 or 84) I spent most of three days at an awards show (the Juno Awards) chasing every kind of audio buzz and hum you can imagine. My tie-in was done by a house electrician, who was of course nowhere to be seen on the strike. When I went to retrieve my tails, the ground wire literally fell out of the terminal...
Title: Re: Overheated Edison Plug
Post by: Geoff Doane on February 13, 2017, 09:45:07 pm
And on a related note, here's why tinning the wires before you clamp them in the plug is not a great idea.

This was probably tight when it was first put together, but after a bit of thermal cycling, not so much.  :(

Title: Re: Overheated Edison Plug
Post by: Scott Helmke on February 14, 2017, 10:03:48 am
Even a properly torqued connector can loosen over time.  I disassemble all my SO cords and re-torque every other year or so.  I always find a couple that need a 1/4 turn on a screw.  It's a nice winter project, and in Minnesota I have a nice amount of winter to spread the work over; though once again the East Coast has gotten way more snow than we have.

We do that too. Usually there are a handful of cables with slightly loose screws, and one or two "OMG I'm glad I found that in time!" scenarios.
Title: Re: Overheated Edison Plug
Post by: Stephen Swaffer on February 14, 2017, 12:37:20 pm
The second thing I noticed on the plug in the OP, after the miswire, was that given the orientation of the wires, it would have ben easier to wire this plug correctly rather than line-neutral reversed.  Why do people work so hard to do things wrong?
Title: Re: Overheated Edison Plug
Post by: Robert Lofgren on February 14, 2017, 12:48:14 pm
Speaking of loose terminal screws. Is it bad code to loctite them?
Title: Re: Overheated Edison Plug
Post by: Daniel Levi on February 14, 2017, 01:01:33 pm
There is a good video of the same problem but with a British plug here: https://www.youtube.com/watch?v=b99n3tesnqY
Title: Re: Overheated Edison Plug
Post by: Tim McCulloch on February 14, 2017, 01:07:10 pm
Speaking of loose terminal screws. Is it bad code to loctite them?

Do not use thread lockers, they are non-conductive.
Title: Re: Overheated Edison Plug
Post by: Jonathan Johnson on February 14, 2017, 05:25:50 pm
Speaking of loose terminal screws. Is it bad code to loctite them?

Sometimes, the problem isn't that the terminal unscrews, but that the conductors flow. Thread locker won't help.

One of the big problems with aluminum wiring -- at least in the smaller gauges -- is that when the terminal heats up, the aluminum (which has a higher thermal coefficient of expansion than copper) tries to expand, but is constrained by the head of the screw and the backing plate. This increased pressure on the aluminum causes deformation -- it tends to squish or flow out the unconstrained side (aluminum is also usually more malleable than copper). Then, when the terminal cools, the deformed aluminum shrinks, and the connection becomes slightly looser than before. Because the connection is looser, the resistance can increase, causing it to heat up more next time. And the more it heats up, the more it deforms and the connection gets looser and looser.

With copper, the problem isn't nearly so onerous, because copper is a little more elastic (resilient) than aluminum, so after the terminal heats and cools, the copper tends to return to its original shape, maintaining the tightness of the connection. Copper oxide is also more conductive than aluminum oxide.

With stranded wire -- even if it's copper -- there can be a problem with these screw terminals in that handling of the cable can cause the strands to wiggle around in the terminal. That wiggling results in the structure of the strands deforming, just as happens with solid aluminum wire. Crimped connections generally constrain all the strands with no space for the strands to wiggle out, so they tend to be reliable.

Probably the best way to combat loose screw terminals in replacement cord ends is to make sure that the strain relief is securely fastened to the jacket of the cable, and to periodically check the terminations, as others here recommend.