Panel buss short circuit

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sndbodkin

sndbodkin

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Blackfoot, Id
Our company was called to check a panel that had a short circuit between the buses. The panel is 277/480 3 phase 30 space with a 225 amp main breaker. No breakers were installed in the bottom 12 spaces of the panel. One of the buss pegs near the bottom of the panel on phase A, that a breaker would bolt to, was melted back and you could see where it had arced to phase C. On the bottom of the bus, each phase had been burnt or melted appearing that an arc had occurred between each of them. This happened once before on the same panel and again after the buses were replaced. Has anyone seen this before? I have been working as an industrial electrician over 30 years and never seen this happen. I would appreciate your input. Thank you
 
synchro

synchro

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What types of loads are on the panell? Is there any induction or dielectric heating equipment?
It's a real WAG, but a defective device like this might put high frequency HV energy on its input lines and create an initial arc that subsequently develops into a high current arc powered by the 480V 60 Hz.
What made me think of this is the damage that Tesla's high frequency HV experiments did to power company generators. Also, how high frequency is often used to help initiate arcs with TIG welders.
 
sndbodkin

sndbodkin

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Blackfoot, Id
synchro said:
What types of loads are on the panell? Is there any induction or dielectric heating equipment?
It's a real WAG, but a defective device like this might put high frequency HV energy on its input lines and create an initial arc that subsequently develops into a high current arc powered by the 480V 60 Hz.
What made me think of this is the damage that Tesla's high frequency HV experiments did to power company generators. Also, how high frequency is often used to help initiate arcs with TIG welders.
Click to expand...

The panel powers motor loads only.
 
sndbodkin

sndbodkin

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Blackfoot, Id
These pictures show where the arcs occurred. This is in a dry environment. No sign of rodents or snakes. No lightning during the time this happened.
 

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Jraef

Jraef

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ptonsparky said:
I suspect you have something entering that cabinet. Moisture. Rodents. Snakes. Lightning. Take your pick. It will do it again, unless you figure it out.
Click to expand...
Yep, something is making this happen. Internal condensation because of cold air coming in from a conduit that goes under ground in a moist area is one possibility. I had one where a compressor drain line was accidentally tied into a conduit, so every time the compressor turned off and the unload valve opened, it blew the tank condensate into the conduit and caused a flashover in the control panel for a different machine. But by the time anyone got to it to look, everything had evaporated, we would never see moisture, only the carbon from the flashover. The only reason we figured it out was when we got a flashover immediately after we heard the compressor turn off and vent.

To be clear, I'm not saying that's what it IS, but that it could be something that you are not expecting that is taking place with regard to moisture or foreign materials getting inside.
 
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synchro

synchro

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Chicago, IL
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I think condensation could show up as more of a problem at the bottom of the busbars. Gravity would cause any drops that appear to migrate toward that end. And it would be cooler there because hotter air rises to the top. And in your case the empty spaces at the bottom of the busses means there's no localized heating in that particular area of the panel.
 
growler

growler

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Atlanta,GA
sndbodkin said:
This happened once before on the same panel and again after the buses were replaced. Has anyone seen this before? I have been working as an industrial electrician over 30 years and never seen this happen. I would appreciate your input. Thank you
Click to expand...

I will assume this panel is at a manufacturing plant. If this is correct, what do they manufacture? Materials used and that sort of thing.

Like others I would think some sort of foreign material has gotten into the panel.Once you rule out the rats and snakes and even moisture then what's left to consider?
 
sndbodkin

sndbodkin

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The panel is inside a dry room that is temperature controlled. The conduit that feeds this panel comes through the wall directly from the meter base. There is no sign of moisture in the panel. The branch circuits feed starters for motors on a grain elevator. Both times this has happened there has been no finding as to why. We are replacing the panel with a complete new on, a different brand, and we are hoping it doesn't happen again. Maybe a different design will solve the problem. I know what you are thinking and I thought the same thing when our service tech called from the job site. Several of our team visited the location and all of us are stumped with this. Usually there is something that jumps out at you. This is not the case.
 
synchro

synchro

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The pictures show the arcing was primarily at the sharpest points or corners on the busbar, and also on the corners of the attached peg for mounting a breaker. Such corners would be where the electric field gradient across open air would be the highest (in other words, where the electric field is changing the most quickly vs. distance). The arcing evidently occurred across an air gap, which is different from arc tracking across an insulator caused by surface contamination or moisture. I could be wrong, but I don't think 480V L-L would normally be sufficient to induce corona and initiate arcing across significant air gaps like that causing the damage in the photos. However, the 480V could likely sustain the arcing once started. For the OP, do you know the approximate distance between the points where the arcing occurred?

I wonder if there could be voltage spikes occurring from the switching of PF correction capacitors, a defective transformer, or something else. Perhaps a surge arrester could be installed on the panel, preferably to clamp significant voltage surges, but also to confirm that a large surge had occurred if the arrester itself was also damaged.
 
sndbodkin

sndbodkin

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Location
Blackfoot, Id
synchro said:
The pictures show the arcing was primarily at the sharpest points or corners on the busbar, and also on the corners of the attached peg for mounting a breaker. Such corners would be where the electric field gradient across open air would be the highest (in other words, where the electric field is changing the most quickly vs. distance). The arcing evidently occurred across an air gap, which is different from arc tracking across an insulator caused by surface contamination or moisture. I could be wrong, but I don't think 480V L-L would normally be sufficient to induce corona and initiate arcing across significant air gaps like that causing the damage in the photos. However, the 480V could likely sustain the arcing once started. For the OP, do you know the approximate distance between the points where the arcing occurred?

I wonder if there could be voltage spikes occurring from the switching of PF correction capacitors, a defective transformer, or something else. Perhaps a surge arrester could be installed on the panel, preferably to clamp significant voltage surges, but also to confirm that a large surge had occurred if the arrester itself was also damaged.
Click to expand...

The distance is 1.25". We have considered to possibility of voltage spikes and are in touch with the utility company to check their end of things. We have installed several surge protectors on some of their facilities, mostly to protect VFD, PLC and other electronic equipment. I think installing a surge protector is a good idea and will suggest it. Thank you so much for all of your input on this matter.
 
Sahib

Sahib

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India
Hmm. If surge were the cause of damage inside the panel, it would not spare the connecting cables in the first place because the distance between the conductors much more less. It would be more prudent to meggar the panel than to install surge arrester.
 
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