What caused this - burned neutrals in panel

[LeeG]

Friend was watching TV. Cable box rebooted, then power went out to the TV a few minutes later. He checked all the breakers, and none were tripped. He called me yesterday and I went over today expecting to find a bad breaker. This is what I saw under the panel cover.

View media item 104943
The neutrals on the other side of the panel were all fine, as were all of the hots. The breakers all tested 120v to the neutral buss.

Home is a fairly new build (10 years or so). Nothing out of the ordinary was happening at the time the power went out.

I told him he needed to get a pro in to check things out, as I've been out of the trade for 30 years and never did anything but industrial even then.

Any one have an idea what is going on so I can at least let him know what to expect?

Thanks
Lee

 

[RECox286]

Probably a loose connection in the neutral.

I can see it working progressively from one

circuit to the next.

Uncle Bob

 

[zmaxmotorsports]

Check all of his connections inside of the panel,check the buss itself to see if theres a loose connection on that side of panel.

 

[LXCam]

Yup, loose.

 

[wyliesdiesels]

Loose connection flared up and roasted the ones above it.

The other possibility is an overloaded neutral on a MWBC that has both hots fed from the same hot leg....

 

[sberry]

You need a wider shot. is the buss between the right and left bar connected?

 

[larry4406]

Same thing happened to me. Lost a circuit but no tripped breaker. Plug tester said "hot neutral reversed". Found one charred neutral at the panel. Killed main and tightened all screws, was able to get 1/2-2 turns on most. On the charred neutral, I had enough slack to trim off the charred portion.

 

[manwithtools]

Definitely loose. Need to check all terminations for proper torque. Kill the main first. It's not a bad idea to check on any panel after it's been installed, I've seen several that were not torqued properly. All electrical terminations have a specified torque, but most electricians just tighten them until they are "tight". The real good ones will use a torque screwdriver or wrench to be sure they are correct. This is especially important on larger gauge terminations.

 

[NUTTSGT]

Ok, now I'm curious here. Granted, I'm not an electrician, nor do I claim to be, but I'm not an idiot either (some may disagree) but can somebody explain this to me ?

As a firefighter and fire investigator, this has me wondering as we do deal with issues like this. I have saved, photoshopped and uploaded that image to my PB account.

Left red circle, I see green corrosion on the bare copper wire next to what I will call the wire of origin. Seeing green corrosion here and no place else tells me, there has been something happening here for longer than just overnight. Why ?

Right red circle, as you have noticed above I mentioned wire of origin. The screw in the circle shows significant heat damage. This tells me more than likely this is the point of origin. Would you guys agree ? Loose screw culprit ?

 

[Hazmat91180]

Ok, now I'm curious here. Granted, I'm not an electrician, nor do I claim to be, but I'm not an idiot either (some may disagree) but can somebody explain this to me ?



As a firefighter and fire investigator, this has me wondering as we do deal with issues like this. I have saved, photoshopped and uploaded that image to my PB account.



Left red circle, I see green corrosion on the bare copper wire next to what I will call the wire of origin. Seeing green corrosion here and no place else tells me, there has been something happening here for longer than just overnight. Why ?



Right red circle, as you have noticed above I mentioned wire of origin. The screw in the circle shows significant heat damage. This tells me more than likely this is the point of origin. Would you guys agree ? Loose screw culprit ?

Are you aware of any type of arcing that occurred in that panel? Given the grounds above also look charred i was thinking a large vertical arc across the neutral buss.

 

[going4speed]

I think that corrosion is a correlation of the heat in the area probably reaching above 350C maybe more. This heat likely broke the corrosion layer of the copper and caused accelerated corrosion in the area.

What's odd to me is the apparent skip level damage of the wire burns. The wire with the trace damage to the grounds appears to have the same damage as the neutral two down. Perhaps this is a result of inadequate torque on the fasteners?

I'm a mechanical engineer so this is truly speculation.

 

[manwithtools]

I think that corrosion is a correlation of the heat in the area probably reaching above 350C maybe more. This heat likely broke the corrosion layer of the copper and caused accelerated corrosion in the area.

What's odd to me is the apparent skip level damage of the wire burns. The wire with the trace damage to the grounds appears to have the same damage as the neutral two down. Perhaps this is a result of inadequate torque on the fasteners?

I'm a mechanical engineer so this is truly speculation.

The corrosion is most likely caused by the heat damage from the neutral and out gassing of it's insulated covering when it melted. While it's hard to determine from the picture, I think the reason the corrosion only occurred on that one spot is due to the neutrals proximity to the ground wires. The neutral two down from it was probably not close enough to the ground wires to effect them.

NUTTSGT - you are right, this has been going on for a while. It's just recently gotten bad enough to cause the owner to notice. I had the same thing happen in a detached shop panel a couple of years ago. I didn't notice it until the lights would not come on one day.

 

[arroberts]

If you look at the circled screw, it appears to be elevated above the rest of them. Either it is a much heavier gauge wire, or it is loose.

 

[Strouty]

I think electricity caused it.


Be happy it didn't do more damage.

 

[NUTTSGT]

I think that corrosion is a correlation of the heat in the area probably reaching above 350C maybe more. This heat likely broke the corrosion layer of the copper and caused accelerated corrosion in the area.

The corrosion is most likely caused by the heat damage from the neutral and out gassing of it's insulated covering when it melted. While it's hard to determine from the picture, I think the reason the corrosion only occurred on that one spot is due to the neutrals proximity to the ground wires. The neutral two down from it was probably not close enough to the ground wires to effect them.

Well, that does make sense. Quite similar to how metal will rapidly rust after being exposed to fire when it's paint or protective oil has burned away.

 

[rlitman]

...The screw in the circle shows significant heat damage. This tells me more than likely this is the point of origin. Would you guys agree ? Loose screw culprit ? ...

I've posted this image before. The picture shows a high of 161F on the scale, but this was after the unit was powered off and had been cooling down while the safety covers were removed. A less pretty picture through the safety grating showed a peak temperature of 408F while still under power. Thankfully we caught it with the FLIR camera before there was a similar failure.

Anyway, that was a metric 10.9 bolt (10mm I think), which had been torqued, connecting a silver plated copper bar to another copper bar. The bolt had a zinc coating that started out looking just like the undamaged screws on this ground bar, and ended up with a similarly dull dark grey appearance to the screw you pointed out. It takes time for this kind of hot oxidation to happen.

I wouldn't expect thermal imagery of home panels to become commonplace anytime soon, but I will say this. If the screws on that bus bar aren't squeaking when you tighten them, they're not tight enough.

 

[going4speed]

What does the consumption side of this wiring look like? As in the outlets on the circuit?

 

[Richard Cranium]

I have seen this kind of damage before with out any damage to the other end. The heat was at the screw, so that is where the heat damage was. The other end of the wire should not be damaged.

 

[wyliesdiesels]

I think electricity caused it.


Be happy it didn't do more damage.

Actually, high resistance caused it!

 

[LeeG]

Thanks for the responses everyone. I didn't see any damage at any of the receptacles on the circuit. What was in the photo was the extent of the damage I discovered. I'll post an update in a few days when I hear back from my friend who owns the house.

 

[ez-duzit]

That wire with green corrosion on it appears to be a black, hot wire, unless that is just from charring. Otherwise the corrosion might have started this failure.

 

[bjcouche]

Nuttsgt,
You are assuming that there was just 1 wire that caused all the visible damage. Consider the possibility that there were several loose wires and only the worst one was noticed by the home owner when the power went out. From what I see there are two wires that could be a "source" and the wires adjacent to those radiating further away, show less damage. I'd guess that several of these wires are loose and only the worst ones or ones with higher current show the most damage. I've done electrical failure analysis before, and sometimes it's hard to determine for sure. I will say that very high temperatures in just a few minutes can cause corrosion that looks like it took years to form.

Brian

 

[Denwood]

I've posted this image before. The picture shows a high of 161F on the scale, but this was after the unit was powered off and had been cooling down while the safety covers were removed. A less pretty picture through the safety grating showed a peak temperature of 408F while still under power. Thankfully we caught it with the FLIR camera before there was a similar failure.

Anyway, that was a metric 10.9 bolt (10mm I think), which had been torqued, connecting a silver plated copper bar to another copper bar. The bolt had a zinc coating that started out looking just like the undamaged screws on this ground bar, and ended up with a similarly dull dark grey appearance to the screw you pointed out. It takes time for this kind of hot oxidation to happen.

I wouldn't expect thermal imagery of home panels to become commonplace anytime soon, but I will say this. If the screws on that bus bar aren't squeaking when you tighten them, they're not tight enough.

This was one of the first things I did with our FLIR ONE, which plugs into an iphone: http://www.apple.com/ca/shop/product/HJ102VC/A/flir-one-for-ios-personal-thermal-imager

If it's not standard home inspection procedure, it should be. It only takes a few minutes to power up, then check the panels and receptacles for hot spots.

 

[manwithtools]

I'd bet on one loose wire causing most of the problem, please realize that all wires connected to a buss bar like that become heat sinks for the high temperatures that occur when the resistance of a single connection becomes very high. We have tested this behavior before in the solar industry, the wires will actually increase the buss bar's singular ability to carry current because the individual wires dissipate some of the thermal energy.

This example is an extreme case. The connection became very hot, therefore the buss bar became hot. The collective wires then become heat sinks very quickly because they are of less mass than the buss bar. Particularly the ones close to the source of the heat.

 

[Aceman]

I'm betting there is a loose connection at the strap the connects the neutral busses together at the top. Or the neutral buss has a crack in it.

 

[klassenl]

Two comments on this.

In my experience I have seen damage like this in junction boxes as well as panels. More than half of the time the damage is on the neutral with no apparent damage to the phase conductors. I agree that loose connections cause this but the amount of times it's on the neutral gives me thinking problems.


Second, for a home inspector to go in with an infrared camera and to start snapping picures is somewhat meaningless. The "hot spots" will only show up under load. If the house has been vacant even for the day all those hot spots will be cold and we won't get an accurate picture of what's going on. The other problem with IR cameras is there can be a lot of heat transfer, especially during heating season.

 

[NUTTSGT]

Nuttsgt,
You are assuming that there was just 1 wire that caused all the visible damage. Consider the possibility that there were several loose wires and only the worst one was noticed by the home owner when the power went out. From what I see there are two wires that could be a "source" and the wires adjacent to those radiating further away, show less damage. I'd guess that several of these wires are loose and only the worst ones or ones with higher current show the most damage. I've done electrical failure analysis before, and sometimes it's hard to determine for sure. I will say that very high temperatures in just a few minutes can cause corrosion that looks like it took years to form.

Brian

I'm learning here and the guys have added some very good information. Assuming, yes possibly you could call it that but more like theorizing, trying to figure out why and how. You have to start somewhere and rule things out from there. . . . prove/disprove.

This example is an extreme case. The connection became very hot, therefore the buss bar became hot. The collective wires then become heat sinks very quickly because they are of less mass than the buss bar. Particularly the ones close to the source of the heat.

Interesting, didn't think of those wires becoming heat sinks. Good point.


Like I mentioned above in the thread, this is not my thread or my picture. In no way am I trying to hi-jack the OP's thread. I just find this very interesting as I can apply this in what I do at work. I appreciate all the comments.

 

[sberry]

I'm betting there is a loose connection at the strap the connects the neutral busses together at the top. Or the neutral buss has a crack in it.

I got to go with Ace here.

 

[bczygan]

So what are the specs for torque for different wire connections?

Bill

 

[BreeStephany]

Doubtful, because it looks resi, which is almost all romex, but any chance of shared neutrals? I have seen burned neutrals where the neutral wasn't correctly sized for a load, but never in a resi setting.

Also.... any chance of a lightning strike? I have seen neutrals and grounds blown apart in a panel after getting hit by lightning... but there was generally a LOT more scorching in the panel than what I see...

Just my two cents... and of course, things to investigate after making sure that the connections are correctly torqued throughout.

 

[dw1]

Well the panel is 10 years old, the wires were "Probably" never correctly tightened and over time and the seasons the connection became worse. I would cut the damaged parts out and re connect the wires and tighten securely...
If you want, mark the wires some way to identify them if it happens again!!, you could always put an amprobe on the white wires to check to see if there is an overload problem. Probably never tightened correctly, but might be a good time to check every termination inside the panel.

 

[manwithtools]

So what are the specs for torque for different wire connections?

Bill

Torque specs are specified by the termination manufacturer. Here is an example of a neutral bar:

4-14,1,14 Neutral Bar (12) circuit , (2) #10 mounting hole wire range 4-14 AWG Neutral/Ground bar, Dual Rated, Aluminum & Copper wire, CU9AL 90C Rating

Torque rating:

• 4 ga - 45 in. lb.
• 8 ga - 40 in. lb.
• 10-14 ga - 35 in. lb.

Any UL listed device must have a torque rating shown on the device or equipment label. There should be a label in the OP's panel that he pictured.

NEC table follows, equipment manufacturer data takes precedence:

 

[going4speed]

Never seen an electrician with a torque wrench. Maybe I was hiring the wrong guys I dont know. I typically tighten the heck out of them. Probably the wrong way but that's what I've seen licensed dudes do around here with forearms like Popeye.

Oh and I've seen them do an annual PMI on a panel and tighten them in a swift movement and you can hear the terminal pop or it that a torque screwdriver they are using?

 

[manwithtools]

As they say "You get what you pay for"

Is that tight enough? Did he strip the threads? .... "You can hear the terminal pop" - please help me, what does that mean?

 

[going4speed]

In the below video 1 minute in. Is that a torque screwdriver?

 

[manwithtools]

No, that's an idiot. Your point?

Look here: http://www.wihatools.com/torque-control-drivers-handles-blades/torquecontrol-tools/torquevario-adjustable-handles

Plenty of other options....

 

[going4speed]

My point is I've seen that done multiple times. Trying to learn what's right.

 

[manwithtools]

going4speed, sorry for the over reaction, glad that you want to learn.


A lot of bad practices demonstrated in the video - hence my comment "No,that's an idiot".

To begin with; the video shows the gentleman working on the main breaker with it turned on, not a good idea. In fact even if he turned it off, the line side of the main breaker would still be live. He should have proper PPE on or he should have power to the panel turned off. Then verify that it is off via a volt-meter.

Waving a screwdriver around inside of a live panel like its a pointer and videoing for the world to see is just negligent. With the main breaker in the on position the buss that the breakers fasten to is still live - see the exposed buss below the breakers?

Then he says that "electricity vibrates" and that loosens terminals - WTF? Oh, then he screws around with his cell phone while he's in the panel, all the while yakking about how you need to hire a "Licensed electrician or insurance won't cover you" ....

The popping sound seems to be coming from the breakers as he checks the tightness. That is not a torque screwdriver as near as I can tell.

To answer your question - yes, there are torque screwdrivers that are made for this task. In our shop where we build UL listed control panels for industrial use, every termination is checked with a torque screwdriver or torque wrench on the larger terminations before shipment.

 

[LeeG]

Here is a good article I found regarding proper tightening on electrical connections.

http://ecmweb.com/contractor/do-you-have-calibrated-arm

A particular quote regarding not using a torque driver:

While the electricians were slightly more likely to over-tighten connections than the entire group of participants, the study revealed they were no better at achieving a proper connection than someone with no experience as an electrician.
Anecdotally, it was obvious during the test that people who had never made an electrical connection before had as much chance of getting it within 20% as an electrician with decades of experience. This indicates that achieving recommended torque is nearly independent of training and experience — and requires the use of a torque wrench to properly tighten a connection.

So why don’t we have more failed connections if most electricians appear to be doing such a poor job of tightening them? The fact is that our electrical system has built-in safety factors, and circuits are rarely fully loaded.

I think I'll go home and check my panels tonight.

 

[BreeStephany]

Never seen an electrician with a torque wrench. Maybe I was hiring the wrong guys I dont know. I typically tighten the heck out of them. Probably the wrong way but that's what I've seen licensed duded do around here with forearms like Popeye.

I always carried torque wrenches and a torque driver with me and torqued everything, especially service mains, to spec. We mostly did commercial and light industrial though, so most of our services were 800A~2500A 3ph 208 & 480v services