# Burnt neutral wires on subpanel



## woodardhsd (Jan 24, 2011)

I have a 12x12 detached workshop at my house that has a small Square D subpanel ( http://www.lowes.com/pd_36242-296-HOM612L100SCP_0__?productId=3134331 ) There are two circuits; one 15A for lighting and a 20A one for receptacles. The lighting circuit has 3 4' fluorescent fixtures and one incandescent outdoor light. 

My wife found a stray kitten and has been keeping it shut out in the shop the last few days. It started to get cold here 2 nights ago so I got a small 600W/900W/1500W forced air space heater. It was pretty crappy, so I got another heater (oil filled radiator, same wattage as the first) It got down to 30 last night so I wanted to run the radiator heater. I started up the radiator heater before I turned off the small one. I think they were both on the 900W setting. They were both on only for a few minutes before I turned the small forced air fan off. I started smelling something burning and traced the smell to the subpanel. I removed the cover and found the two neutral wires had 2 inches of burned insulation, and the neutral bar had melted some of the plastic it was attached to. I checked and none of the screws were loose where they connected to the bus bar.

I believe all the light fixtures were on at the time as well, but that should have been less than 300W.

I don't think I overloaded either circuit, and the hot wires were not even warm. Shouldn't the breakers have tripped if I had overloaded the circuits?


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## curiousB (Jan 16, 2012)

Loose connections will cause wire to heat up. Also if the wires were knicked.

Are you sure the wires burned this time? Maÿbe it happened long ago.

You could try re striping the wires above the burn if enough slack and re attach to bar.

Then run you heaters and using a non contact ir thermometer see if the bar is hot or warming.


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## woodardhsd (Jan 24, 2011)

curiousB said:


> Loose connections will cause wire to heat up. Also if the wires were knicked.


The connections were tight. I'm not sure if the wires were nicked, I can check to make sure.



curiousB said:


> Are you sure the wires burned this time? Maÿbe it happened long ago.


I'm almost positive it happened yesterday, I smelled the burning insulation for the first time, and the outside of the subpanel was very warm.


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## Stubbie (Jan 7, 2007)

Did you check the feeder neutral lug? Check at both ends and power off.


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## woodardhsd (Jan 24, 2011)

Stubbie said:


> Did you check the feeder neutral lug? Check at both ends and power off.


Yep, it was tight as well. What do you mean both ends?


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## jbfan (Jul 1, 2004)

The end inside the main panel.
Burnt happens because of loose connections.
Do you have gfci's in this shed?


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## woodardhsd (Jan 24, 2011)

jbfan said:


> The end inside the main panel.
> Burnt happens because of loose connections.
> Do you have gfci's in this shed?


Ok, gotcha. I didn't think to check that connection as it's about 100' between the main panel and the subpanel. 

The first receptacle in the circuit is GFCI, the rest are not.


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## Removeb4flight (May 12, 2013)

Did the 20 amp circuit accidentally get wired with 14 gauge wire?


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## woodardhsd (Jan 24, 2011)

No, both circuits are wired with 12 gauge.


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## curiousB (Jan 16, 2012)

how is panel fed from main panel? 4 wire (blk, red, white, ground)? what gauge? what is feeding breaker size? A ground rod at the shed? Any other feeds to that shed?

Just wondering if there is some strange return path overloading the neutral. Seems unlikely.


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## woodardhsd (Jan 24, 2011)

There is 20' of 10/3 cable run from a double 20A breaker at the main panel (located in the middle of the house) to an attached storage/water heater room at the back of the house to a junction box. From that box there are 4-10GA THHN wires that run through conduit out to the shop. The THHN wires are connected directly to the neutral bar, ground bar, and the double 20A main breaker. There are the two circuits, wired with 12/2 cable, one for receptacles and one for lighting. No ground rod, no other feeds to the shed.


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## curiousB (Jan 16, 2012)

Do you get 240 VAC when you measure across the two phases in the shed panel? I am wondering if someone incorrectly used a double breaker (two breakers fed from one phase) to feed the MWBC (feeder to shed) instead of a dual pole breaker (two breakers, each fed fed from a different phase). 

If they were from the same phase then it is possible the neutral is overloaded.


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## jcrack_corn (Jun 21, 2008)

almost certainly a shared neutral situation.


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## dmxtothemax (Oct 26, 2010)

If your shed sub panel has a ground rod that is bonded ?
Then your neutral could be carrying extra current from
some one nearby who has a poor neutral.


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## zappa (Nov 25, 2011)

Threads can bind up sometimes making you think it's tight but the wire is still loose. Based on your description there has to be a poor connection(s) on the neutral bar somewhere.


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## woodardhsd (Jan 24, 2011)

jcrack_corn said:


> almost certainly a shared neutral situation.


How do I confirm this? 

There is no ground rod, and the neutral is not bonded


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## dmxtothemax (Oct 26, 2010)

The two most likely suspects are loose wires in neutral bar
Or plain old overloading.

Check post 12,
That sounds like a good ex planation for
your symptoms.

Replace the neutral bar
Chop out any damaged cable
when done, observe the neutral bar with an IR camera
A lot of people have phones with IR camera's
find one and use it.

If it still seems to heat up too much
then you have to find what's overloading the system


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## dmxtothemax (Oct 26, 2010)

woodardhsd said:


> How do I confirm this?
> 
> There is no ground rod, and the neutral is not bonded


Check that it is a real 240v set up,not two 120v lines.

Check with a volt meter across the two hots
it should read 240v or there abouts.

If it reads almost nothing then its probably
two 120v lines.

Can you post a picture of your panel ?
Showing the relevant breaker


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## jcrack_corn (Jun 21, 2008)

woodardhsd said:


> How do I confirm this?
> 
> There is no ground rod, and the neutral is not bonded


may be hard to do if you dont know what to look for...as mentioned above measure between the "phases"/ poles. if a neutral is shared between two poles, then it sees no current for equal loads (so if each leg is pulling 15a, the neutral sees zero)....if it is a shared neutral (or neutrals) on a single pole then the neutral sees the ADDITION of each circuit (or 30 amps in the above example)


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## woodardhsd (Jan 24, 2011)

My multimeter has decided to stop reading AC volts tonight so I can't do that test. Here are a couple of pictures of the panel itself, and then a closer view of the neutral bus bar and the burnt wires.

Please go easy on me regarding the 4 green THHN feeder wires. I thought I would save a few bucks ordering one spool of wire. I didn't realize it was against the rules to re-code wire colors, and I haven't got around to pulling new ones.


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## curiousB (Jan 16, 2012)

Given the green wires are you sure you haven't mixed up neutral and ground?

also what about a similar picture from the house panel. I wanted to see the feeding breaker and wires there...


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## Jnaas2 (Mar 29, 2014)

Im taking it the 20amp double pole is your main breaker with the green wires connected to it, Why are you back feeding into it and are you sure the feeds and neutrals are correct. That panel doesnt need a main breaker its at your main panel, Do away with the back feeding breaker and make sure you dont have the feeds and neutrals reversed, Some breakers wont work like that


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## Jump-start (Sep 26, 2012)

That panel has several violations that need to be corrected first.


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## Stubbie (Jan 7, 2007)

You may have had the neutral wires insulation underneath the terminal screw or screws preventing good contact with the neutral bar. 

If both heaters were on 900w that would be 1800 watts which is the max for a 15 amp circuit. However I would suspect the heaters were on the 20 amp circuit ... that circuits neutral appears to be the hot point connection to the neutral bar. The other damage could just be the end result.

There are code violations as you know with he installation.

If all the violations are forgotten (for now) the panel would appear to be wired correctly assuming of course the green wires are connected at the junction box correctly and at your panel. It would have been real easy to screw that up .... :wink:


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## sparky90 (Aug 1, 2014)

How come you are not feeding the lugs???????????????????????


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## Stubbie (Jan 7, 2007)

Jnaas2 said:


> Im taking it the 20amp double pole is your main breaker with the green wires connected to it, Why are you back feeding into it and are you sure the feeds and neutrals are correct. That panel doesnt need a main breaker its at your main panel, Do away with the back feeding breaker and make sure you dont have the feeds and neutrals reversed, Some breakers wont work like that


The panel is designed for a backfed main breaker and it is required that the detached shed has a means of disconnect be it main breaker or other method. It does need the hold down kit installed on the main breaker. You can see the standoff where it attaches.


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## Desertdrifter (Dec 10, 2009)

Green to green 120v
Green to green 120v
Green to green 240v
Green to green 0.1v

IMHO, At least mark your wires, hots, red and black, neutral white and check the feed to make sure they match. So that all is copacetic.


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## Jump-start (Sep 26, 2012)

clw1963 said:


> Green to green 120v
> Green to green 120v
> Green to green 240v
> Green to green 0.1v
> ...


I agree. In the very least its a really good idea. Technically per code you cant remark a green or wires that are not part of a cable assembly until they are a certain size, but in this case its better than nothing.


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## Desertdrifter (Dec 10, 2009)

Exactly, not expecting to redo his project. But may help in troubleshooting. I'd ring out the neutral and ground back to the feed. I see No reason those wires should have cooked as it is basic wiring. Maybe something amiss at the feed.


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## Jump-start (Sep 26, 2012)

clw1963 said:


> Exactly, not expecting to redo his project. But may help in troubleshooting. I'd ring out the neutral and ground back to the feed. I see No reason those wires should have cooked as it is basic wiring. Maybe something amiss at the feed.


Same, a lot is wrong imo. Anything could have fried the noodles, but Im leaning toward partially tightened screws or a Stubbie mentioned those wire being inserted without being stripped first.


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## woodardhsd (Jan 24, 2011)

curiousB said:


> Given the green wires are you sure you haven't mixed up neutral and ground?
> 
> also what about a similar picture from the house panel. I wanted to see the feeding breaker and wires there...


I had marked all the wires before I pulled them through, so I'm 99% sure they are hooked up right.

I can try to get a picture in the next couple days. It's warmed back up here so the heaters don't need to run for a few days.



clw1963 said:


> IMHO, At least mark your wires, hots, red and black, neutral white and check the feed to make sure they match. So that all is copacetic.


I meant to re label the wires with electrical taps or heat shrink in the appropriate color, just haven't got around to it. I hadn't had any problems with the panel in the 3 years since I installed it.



Stubbie said:


> The panel is designed for a backfed main breaker and it is required that the detached shed has a means of disconnect be it main breaker or other method. It does need the hold down kit installed on the main breaker. You can see the standoff where it attaches.


So the back fed breaker is correct right? I remember researching it on here a few years ago and I thought that was what I read for a detached structure. Completely forgot about the hold down kit, that wasn't something I could find at Lowe's.



Jump-start said:


> That panel has several violations that need to be corrected first.


Such as? Any others that haven't been mentioned?


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## Stubbie (Jan 7, 2007)

Yep your fine with the main breaker being backfed. You need this hold down kit HOM1RKCP. Do a google search with those numbers and several vendors will be listed


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## woodardhsd (Jan 24, 2011)

Stubbie said:


> Yep your fine with the main breaker being backfed. You need this hold down kit HOM1RKCP. Do a google search with those numbers and several vendors will be listed


Ok, I remember looking that kit up. It wasn't available at Lowe's (still isn't) and I just forgot to order it from somewhere else.



Jump-start said:


> Same, a lot is wrong imo. Anything could have fried the noodles, but Im leaning toward partially tightened screws or a Stubbie mentioned those wire being inserted without being stripped first.


Those wires were definitely stripped before. It's hard to tell from the picture, but you can see up close where the insulation stops.


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## Stubbie (Jan 7, 2007)

Your panel has a few code violations as you know but the 4 wire feed is correct and the neutral separated from ground is also correct. I would only suggest that you correct those green wires ... per NEC. I already gave you the hold down kit they are less than 3 bucks and takes about 1 minute to install...

The picture of the overheated neutrals is classic poor connection. Might have only been one of them but got so darn hot it melted the panel and insulation on the other neutral. Be sure the feeder is 4 wires all the way back to the main panel (service equipment). You might check the cable clamps where your nm is entering the loadcenter to make sure they are not over tightened cutting the insulation,.. Breakers won't trip when the problem issue is on the neutrals unless there is overcurrent on the ungrounded (hot) conductor. I still think it is either a loose connection or poor connection on the 20 amp circuit at the neutral bar.


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## Stubbie (Jan 7, 2007)

Also as Curious B mentioned be sure your breaker at the main panel is a double pole breaker connecting to opposite hot legs or measure voltage at your sub to be sure you have 240 volts between the hot bus bars.


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## woodardhsd (Jan 24, 2011)

The breaker at the main panel is a double pole breaker just like the one I'm using as a main at the sub panel. I think it's a Eaton BR220 breaker since it's an Eaton panel. I can pull the front of the panel off to be sure, but it's almost guaranteed to be on opposite hot legs, right?

As far as repairing the burnt neutrals, do I just need to cut off the wire where the burnt insulation stops, re-strip, and then reconnect to the neutral bar at another screw? At the left end of the neutral bar, the plastic the bar attaches to is melted. Is that going to be a problem?


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## Stubbie (Jan 7, 2007)

> The breaker at the main panel is a double pole breaker just like the one I'm using as a main at the sub panel. I think it's a Eaton BR220 breaker since it's an Eaton panel. I can pull the front of the panel off to be sure, but it's almost guaranteed to be on opposite hot legs, right?


 Sounds like your fine if you have a voltage tester you can test voltage at the sub panel in the shed. Test for 240 volts between the two unused hot lugs.



> As far as repairing the burnt neutrals, do I just need to cut off the wire where the burnt insulation stops, re-strip, and then reconnect to the neutral bar at another screw?


 That works .... might have to push the nm into the box to get enough slack. The insulation may be very hard to strip even where it isn't burnt due to the heat. 



> At the left end of the neutral bar, the plastic the bar attaches to is melted. Is that going to be a problem?


 Not likely


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## Jump-start (Sep 26, 2012)

Stubbie said:


> Sounds like your fine if you have a voltage tester you can test voltage at the sub panel in the shed. Test for 240 volts between the two unused hot lugs.
> 
> 
> 
> ...


:no: Id seriously swap the guts. Even if the plastic is ok the heat can ruin the neutral bar terminals. Don't take chances with heat damaged equipment.


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## Stubbie (Jan 7, 2007)

Jump-start said:


> :no: Id seriously swap the guts. Even if the plastic is ok the heat can ruin the neutral bar terminals. Don't take chances with heat damaged equipment.


 I wouldn't argue with that but as the op said he is going to move the connections to the terminals not affected by the heat. Shouldn't be a problem. The entire panel is only about 35 bucks. The guts will cost him more than that at an electrical supply and they will have to special order it. The bigger issue is whether or not we have figured out what caused the overheat.


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## zappa (Nov 25, 2011)

Stubbie said:


> The bigger issue is whether or not we have figured out what caused the overheat.


I can't think of a tactful way to say this Stubbie. You and everyone who spends time on this forum should know it has to be a poor/loose connection to cause this kind of localized heating. It's physically impossible to be anything else. And I agree that the right side of the neutral bar is in like new condition.


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## Jim Port (Sep 21, 2007)

While every indication of a loose connection is seen the OP said every connection was tight.


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## Stubbie (Jan 7, 2007)

zappa said:


> I can't think of a tactful way to say this Stubbie. You and everyone who spends time on this forum should know it has to be a poor/loose connection to cause this kind of localized heating. It's physically impossible to be anything else. And I agree that the right side of the neutral bar is in like new condition.


I think it would be redundant to continue to say this was caused by a loose connection. Like I said earlier this is a classic example of loose connection(s). However electricity is a strange beast at times so I learned a long time ago to never say "it has to be".


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## zappa (Nov 25, 2011)

Jim Port said:


> While every indication of a loose connection is seen the OP said every connection was tight.


Not to bash the OP but "tight" is subjective. There also could have been oxidation or even so tight that the conductor was pinched and heated up at the transition point. If the circuit was heavily overloaded and the breaker is faulty the heating would have extended much further on the conductor. Also the matching circuit wire would be melted.


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## jcrack_corn (Jun 21, 2008)

something is wrong....the green feeding the neutral buss is pristine.

it should have at least some discoloration given the heat.

was there a PREVIOS problem in this panel OP that you pulled new feeders for?


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## Stubbie (Jan 7, 2007)

jcrack_corn said:


> something is wrong....the green feeding the neutral buss is pristine.
> 
> it should have at least some discoloration given the heat.
> 
> was there a PREVIOS problem in this panel OP that you pulled new feeders for?


Why don't you just call the op a liar and be done with it ....


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## curiousB (Jan 16, 2012)

I'm still waiting to hear confirmation there is 240 in this sub panel. I wonder if both phases are the same due to a double breaker at main panel instead of a two pole. Other than loose screw on the neutral wires it's the only scenario I can think of that would stress the neutral.


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## zappa (Nov 25, 2011)

curiousB said:


> I'm still waiting to hear confirmation there is 240 in this sub panel. I wonder if both phases are the same due to a double breaker at main panel instead of a two pole. Other than loose screw on the neutral wires it's the only scenario I can think of that would stress the neutral.


I don't see how this would matter curious. The green feeder neutral looks in fine shape.


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## ritelec (Aug 30, 2009)

Stubbie said:


> Yep your fine with the main breaker being backfed. You need this hold down kit HOM1RKCP. Do a google search with those numbers and several vendors will be listed





Stubbie said:


> The panel is designed for a backfed main breaker and it is required that the detached shed has a means of disconnect be it main breaker or other method. It does need the hold down kit installed on the main breaker. You can see the standoff where it attaches.


It's designed for main lug

And I believe it's ok with six throws of the hand.


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## Jump-start (Sep 26, 2012)

Stubbie said:


> I wouldn't argue with that but as the op said he is going to move the connections to the terminals not affected by the heat. Shouldn't be a problem. The entire panel is only about 35 bucks. The guts will cost him more than that at an electrical supply and they will have to special order it. The bigger issue is whether or not we have figured out what caused the overheat.


 
For 20 bucks that panel can be bought from HD and just to have the guts swapped. Easy piece of mind imo.

But in any case I do agree that the over heating needs to be looked into.


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## Jump-start (Sep 26, 2012)

Jim Port said:


> While every indication of a loose connection is seen the OP said every connection was tight.


Just to add, if a connection is severally over tightened, it can crush the conductor and/or strip the threads to the point the connection becomes poor. Its one out of several possibilities.


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## Desertdrifter (Dec 10, 2009)

Gremlins


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## curiousB (Jan 16, 2012)

zappa said:


> I don't see how this would matter curious. The green feeder neutral looks in fine shape.


Because if they are opposite phases the neutral current Is the difference of the two currents. If they are the same phase then they are additive. If the green wire is heavier gauge than the branch circuits then it might not heat up as much.

I agree most logical is a loose wire(s) on neutral bus though.


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## zappa (Nov 25, 2011)

curiousB said:


> Because if they are opposite phases the neutral current Is the difference of the two currents. If they are the same phase then they are additive. If the green wire is heavier gauge than the branch circuits then it might not heat up as much.
> 
> I agree most logical is a loose wire(s) on neutral bus though.


But even if he had two of the same phases running to the shed the extra current would only be on the green feeder neutral. The branch circuits wouldn't know the difference. Am I missing something?


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## zappa (Nov 25, 2011)

I see what you are saying but both branch circuits have their own neutral so they should never get excessive current from the other circuit. Non-subtracting, but not excessive.

Also, the OP confirmed he had a 2 pole breaker feeding the sub.

ETA: In post 36


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## Desertdrifter (Dec 10, 2009)

Make the repairs and try the same set up again and monitor the wires for overheating. Amp check if you can in case a heater malfunctioned. 
If no ill effects occur. Good to go.

IMHO

PS, Please mark your wires and verify 240v just to know what you have for future.


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## Jump-start (Sep 26, 2012)

zappa said:


> But even if he had two of the same phases running to the shed the extra current would only be on the green feeder neutral. The branch circuits wouldn't know the difference. Am I missing something?



Correct, however both home runs aren't MWBCs. Both would be protected at 20amps, so even if both are on the same phase, because they each have
a dedicated neutral the neutral would be immune from overheating. The buss bar itself is rated as much as the panel, 60, 100 or 125 amps or something similar. The main neutral however could overheat since the current would add. By the looks of it the main neutral lug and wire look ok. 

From looks of it its severe localized heating caused by either one or both terminations being incorrect in some way.


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## zappa (Nov 25, 2011)

Curious is a smart dude and I started doubting myself. Too much thinking...


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## Jump-start (Sep 26, 2012)

zappa said:


> Curious is a smart dude and I started doubting myself. Too much thinking...


He learns his stuff well :thumbup:


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## Stubbie (Jan 7, 2007)

ritelec said:


> It's designed for main lug
> 
> And I believe it's ok with six throws of the hand.


 It is designed for both. It comes with labels for identifying the main breaker if you chose to configure it that way. That particular panel the main goes in positions 1 and 2 where the hold down standoff is located.
You can see it in the picture. 

Yes you can use the lugs and the 6 throw rule. You can also feed another panel with the lugs using a main breaker. This is a very common panel for detached buildings I've installed several.


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## Stubbie (Jan 7, 2007)

Jump-start said:


> For 20 bucks that panel can be bought from HD and just to have the guts swapped. Easy piece of mind imo.
> 
> But in any case I do agree that the over heating needs to be looked into.


Must be your part of the country looking at my local HD it is just over 35 bucks but its irrelevant. I agree an inexpensive fix and piece of mind. He asked me about the melted plastic I simply gave him an answer . If it was my job I'd replace the panel or guts...

Wait ... your correct I brought up the outside weather rated panel so 20 bucks it is....


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## ritelec (Aug 30, 2009)

dmxtothemax said:


> Then your neutral could be carrying extra current from
> some one nearby who has a poor neutral.


Or from four states away !!!! 

My experiment worked !!!!

I give you my current flow. !!!!

Today North Carolina. 
Tomorrow the world. !!!!


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## woodardhsd (Jan 24, 2011)

zappa said:


> Not to bash the OP but "tight" is subjective. There also could have been oxidation or even so tight that the conductor was pinched and heated up at the transition point. If the circuit was heavily overloaded and the breaker is faulty the heating would have extended much further on the conductor. Also the matching circuit wire would be melted.


Is there a specific torque value for those screws? They were tight when I first inspected them after seeing the damage. 



jcrack_corn said:


> was there a PREVIOS problem in this panel OP that you pulled new feeders for?


Everything was installed brand new in 2011, all work done by myself. :whistling2:


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## jbfan (Jul 1, 2004)

woodardhsd said:


> Is there a specific torque value for those screws? They were tight when I first inspected them after seeing the damage.
> 
> All electrical connections have a torque valve, but not many have the tools to make them.
> The value will be listed somewhere on the panel.
> ...


Really? I would never have guess that!!:jester:


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## woodardhsd (Jan 24, 2011)

Sure enough, right on the panel 20 lb-in for #14-10 wire.


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## jbfan (Jul 1, 2004)

What part of NC?


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## ritelec (Aug 30, 2009)

Was thinking To a main breaker would probably be the way to go with the 10's
Looks like the main lugs are rate 8 - 1 so some splice would have to be made. 

I also like the quick disconnect feature on this panel.


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## curiousB (Jan 16, 2012)

woodardhsd said:


> The breaker at the main panel is a double pole breaker just like the one I'm using as a main at the sub panel. _* I think*_ it's a Eaton BR220 breaker since it's an Eaton panel. I can pull the front of the panel off to be sure, but it's almost guaranteed to be on opposite hot legs, right?



You should measure across the phases at the shed to be 100% sure. Will take about 4 seconds of effort. There is something seriously wrong here and after five pages of posts the solution seems to be strip the wire back and reconnect and hope that is the problem. 

That plastic melting was pretty severe, you need to understand root cause for peace of mind. I still think it is loose screws on the neutral wires (or some contamination) but it isn't certain.

Otherwise those kitties with be BBQ.


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## woodardhsd (Jan 24, 2011)

curiousB said:


> You should measure across the phases at the shed to be 100% sure. Will take about 4 seconds of effort. There is something seriously wrong here and after five pages of posts the solution seems to be strip the wire back and reconnect and hope that is the problem.
> 
> That plastic melting was pretty severe, you need to understand root cause for peace of mind. I still think it is loose screws on the neutral wires (or some contamination) but it isn't certain.
> 
> Otherwise those kitties with be BBQ.


My multimeter died, just haven't had a chance to go pick up another one. Hopefully today.

The breaker in the main panel is like the one on the left in the photo. The "i think" part referred more to the brand/amps of the breaker.


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## Stubbie (Jan 7, 2007)

> The breaker in the main panel is like the one on the left in the photo. The "i think" part referred more to the brand/amps of the breaker


 You can check for 240 volts but it is almost certain your fine on voltages. Your breakers in the sub are adjacent and this would put them on opposite legs. Your house panel has a double breaker like the one in the subpanel being used as your backfed main disconnect. Checking can't hurt just to clear up the issue. Problem is a shared neutral could not cause the problem you have. If that were the case as mentioned earlier that problem would show up on your feeder neutral based on the way your branch circuits are wired. The feeder neutral is 10 awg copper and your not loading it anywhere near a point where you would have problems also your .. backfed main is 20 amps so it would trip if that much current was flowing on the feeder. As I said earlier this is classic loose/poor connection at the neutral bar. 

I can only guess that running the heaters placed more amperage on the connections than in the past and the heating problem showed its ugly head. I am somewhat concerned that *both* the lighting circuit and the receptacle circuit neutrals burned as badly as they did. This might be possible if you had the heaters divided one on the lighting circuit and one on the receptacle circuit. Best thing I can tell you based on what I see is to remake the connections and move to different terminations on the neutral bar. See what happens while you turn the heater(s) back on ... But like jump start said you really should replace the panel for only 20 bucks and some change.


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## Stubbie (Jan 7, 2007)

One other issue is what rielect said about the lugs not accepting wire smaller than 8 awg . I meant to bring that up earlier but the fact is your connection at the neutral lug for the feeder is not compatible for 10 awg wire. May not have any problems but all of us are just pointing out things that were done incorrectly. It would be to your benefit to correct all problems with the installation ... :thumbsup:


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## ritelec (Aug 30, 2009)

Ok. You didn't bite on the quick disconnect of the panel 

This last summer someone was installing an in ground pool. 

The backhoe grabbed the 1 " feeding the garage and ripped through it grabbing the 6's feeding the main lugs of the panel. 

By quick disconnect I meant it was nice how the busses disconnected themselves from the plastic mounting strips and slid up to the connector entering the panel. 

No damage to the panel. Like it was designed to do that. 


Ok. As you were.


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## woodardhsd (Jan 24, 2011)

Stubbie said:


> One other issue is what rielect said about the lugs not accepting wire smaller than 8 awg . I meant to bring that up earlier but the fact is your connection at the neutral lug for the feeder is not compatible for 10 awg wire. May not have any problems but all of us are just pointing out things that were done incorrectly. It would be to your benefit to correct all problems with the installation ... :thumbsup:


Whats the best way to remedy that? Can I just run the neutral feeder wire to one of the screws on the neutral bus bar? Or do I need to splice a larger wire to the feeder?


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## ritelec (Aug 30, 2009)

Yep. To the bar. Now you're thinking.


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## curiousB (Jan 16, 2012)

woodardhsd said:


> Whats the best way to remedy that? Can I just run the neutral feeder wire to one of the screws on the neutral bus bar? Or do I need to splice a larger wire to the feeder?


ditto neutral feeder to the bar where you have proper screw size. 

That said I doubt the feeder is the problem. There is no sign of heat there. All the thermal seem to be at the other end of the neutral bar where the melting plastic bar holders are more pronounced. 

I still think most likely is loose screw to branch neutrals or some contamination on stripped neutral wires or the neutral bar.


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## woodardhsd (Jan 24, 2011)

I can now confirm that I have 120V at each hot lug, and 240 between the two hot lugs.

I'm going to see if i can get those burnt wires taken care of this weekend. I have also ordered the breaker hold down kit. What is the best way to label the green THHN wires? Wrap them with the appropriate color electrical tape? Find some colored heat shrink tubing?

Thanks for all the help so far, I'll be sure to post the finished product.


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## Desertdrifter (Dec 10, 2009)

What's easiest and does the job. 
For me that would be tape.


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## Jump-start (Sep 26, 2012)

woodardhsd said:


> I can now confirm that I have 120V at each hot lug, and 240 between the two hot lugs.
> 
> I'm going to see if i can get those burnt wires taken care of this weekend. I have also ordered the breaker hold down kit. What is the best way to label the green THHN wires? Wrap them with the appropriate color electrical tape? Find some colored heat shrink tubing?
> 
> Thanks for all the help so far, I'll be sure to post the finished product.


Electrical tap comes in different colors. Best option would be to re-pull the conductors, but if that is impossible Black and Red is good for the hots, White for the neutral, and the ground can skip out.


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## woodardhsd (Jan 24, 2011)

Jump-start said:


> Electrical tap comes in different colors. Best option would be to re-pull the conductors, but if that is impossible Black and Red is good for the hots, White for the neutral, and the ground can skip out.


It's definitely possible to re-pull the wires, but I would rather not have to. It was kind of a pain the first time, plus the cost as well. Could I re-use one of the green wires as the ground if I decided to do so? Is there a cheaper place to buy wire by the foot than Lowes? It's $0.57 per foot, and I need about 105' for each conductor.


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## curiousB (Jan 16, 2012)

Get some colored heat shrink tubing. Shrink a 3"-4" length on the two hots and neutral. Red, black, white.

http://www.harborfreight.com/120-piece-heat-shrink-tubing-set-67530.html

http://www.ebay.com/itm/70pcs-8Size...Shrink-Tubing-Sleeving-Wrap-Kit-/400742424869


http://www.ebay.com/itm/ENKAY-HEAT-...NT-12-INCH-2-BAGS-18-PIECES-NEW-/311155090908


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## Jump-start (Sep 26, 2012)

woodardhsd said:


> It's definitely possible to re-pull the wires, but I would rather not have to. It was kind of a pain the first time, plus the cost as well. Could I re-use one of the green wires as the ground if I decided to do so? Is there a cheaper place to buy wire by the foot than Lowes? It's $0.57 per foot, and I need about 105' for each conductor.




I don't believe from a safety standpoint anything would happen, but it is technically against code. If a Home inspector ever inspected this during a home closing he will call it out.


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## curiousB (Jan 16, 2012)

View item: 10 GAUGE THHN WIRE STRANDED PICK 3 COLORS 100 FT EACH THWN 600V CABLE AWG End Time: Dec 5, 2014, 4:44:15 PM EST



http://pages.ebay.com/link/?nav=item.view&alt=web&id=291287562578


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## woodardhsd (Jan 24, 2011)

I may have found the smoking gun, but I'll let you guys weigh in. Here is a photo of the burnt pieces of wire where they attached to the neutral bus bar. The one on the top is from the circuit that feeds the light fixtures. The bottom one is the one that powers the receptacles that the heaters were plugged into.


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## ritelec (Aug 30, 2009)

I don't see it. What are you suggesting was the smoking gun?

hint? multiple choice?


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## Desertdrifter (Dec 10, 2009)

Appears the 20amp one isn't dimpled from the set screw being tight. Is my guess. The other has clean copper. 

I do see a little dimple but not clean. Still just a guess.



curiousB said:


> Loose connections will cause wire to heat up. Also if the wires were knicked.


First reply


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## Stubbie (Jan 7, 2007)

Yep that's it ... :thumbsup:


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## ritelec (Aug 30, 2009)

I see the indents on both from screws. 
Don't see nicks. Looks like that's where the insulation was when it started to burn 
Enough for the burn?? 

Seen that and worse along the way. 

Even though the indent is there I think it was loose or not touching 

Don't know. 

Spilt milk.


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## ritelec (Aug 30, 2009)

Was thinking. 

The connection point. 

When the wire is inserted into a terminal. 

How does the current know that it is supposed to go where the screw makes a sound connection to the copper. 
I mean how does if know not to get off where the conductor first touches the bar.

Actually at the hole the wire is inserted in but much like the wire was stripped long laying(touching) on the bar then inserted in the hole and screwed tightly down.

To me the current would get off where the conductor was laying on or touch the bar before the sound connection. So the connection is not loose but doing the same thing as if it was. 

Question. What prevents current from getting off when it first touches the connection point before the screw?


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## zappa (Nov 25, 2011)

ritelec said:


> Question. What prevents current from getting off when it first touches the connection point before the screw?


Sorta the same as the statement, current takes all paths and the amount of current depends on resistance. I know this is not exactly what you are asking but if you used a plastic screw then the current would be the greatest directly behind the screw with very small amounts distributed along the backside depending on the resistance.

Look at it like a parallel resistance circuit. The screw and backside would be like a (say) .1 ohm resistor and the rest that is in contact would have higher resistances with much less current.


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## Desertdrifter (Dec 10, 2009)

To me it's going to come down to surface area and quality of connection. 

Same thing happens to loose connections of any wire size. They will perform ok with little load, apply a lot and they get hot.


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## zappa (Nov 25, 2011)

clw1963 said:


> To me it's going to come down to surface area and quality of connection.
> 
> Same thing happens to loose connections of any wire size. They will perform ok with little load, apply a lot and they get hot.


Same thing I said with fewer words. I think he was mainly wondering about the conduction of the areas that were not touching the screw or directly behind the screw.

The same holds true for a good connection vs. a poor connection but the resistance values would have to be adjusted higher for a poor connection.


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## curiousB (Jan 16, 2012)

ritelec said:


> How does the current *know *that it is supposed to go where the screw makes a sound connection to the copper. _*>>>>>It doesn't, every contact point will create a path across the junction. Think of it an infinite number of small resistors across two mating surface. All of these resistors are in parallel. The resistors tightened down firm will have a lower value that one just loosely touching. So more current will migrate to where the contact is tightest.
> 
> If you don't secure high current connections you start seeing iR voltage drops because the junction point is too loose (i.e. its resistance is too high). The power generated in that same junction becomes i^2R watts. So heating of that poor connection goes up with the square of current. This is a great example of why you need to tighten things well (and why backstab connections are insane).
> *_


*To OP:* Between a firm setting of the bus screws and moving the neutral feeder to a smaller hole on the bus you should have this mystey behind you.


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## zappa (Nov 25, 2011)

ritelec said:


> Question. What prevents current from getting off when it first touches the connection point before the screw?


Adding more to what I have already typed. Your question, and the ohm values that I made reference to but didn't mention are so low that this is not normally considered a problem or even thought about.

Say the conductor and bar had a coating of oxidation that gave you 100 ohms where the conductor first touches the bar. Then take the *resistance difference* from the screw pressure point to the edge of the bar in both the bar and the conductor material. Do you see what I'm getting at? The value is so low that you may as well call it zero. So you are placing 100 ohms across basically zero ohms which isn't even worth mentioning for a current path.



Edit: Wow curious....I can't believe it took me over 23 minutes to write this. I think they are saying the same thing though. :laughing:


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## ritelec (Aug 30, 2009)

Thank you


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## GrampaDave (Dec 4, 2014)

I hope the OP tells us whether his rework worked.

For the record, I too can't see any way to cook the whites ONLY, except for a glowing connection.

Dave


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## woodardhsd (Jan 24, 2011)

I have replaced the section of wire that ran to the 20A receptacle circuit. I was able to pull a bit more of the lighting circuit wire into the box and cut off the burnt section there. I have also installed the breaker hold down kit. 

I haven't had any issues since, but then again, I haven't put the circuits under much load since the repair. I still plan on remarking the wires, but it as been way down on the priority list.


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