This panel is an old GE type. Set of conductors out of PT/CT cab into the top of the panel and a set to the bottom. Top is for Gen Load and Bottom for HVAC. Two meters. As you can see there was a fire. Some of the neutral lugs burned completely off. A and C phase buss melted and started to drip on netral buss. I am not sure what caused this. All wires and connections in metering cabinet showed no signs of a problem. This confused me at first, because I thought perhaps there was a fault and current was looking for ground, hence why the nutral lug(s) where melted. But.. the ground lug on this panel was fine. Ohter than signs of heat from the melt down. Looking closelt at the bottom of the buss, what I think might have happened is the insulator btween the back of the buss and the can, either diintegrated form age and heat or whatever, and caused a direct short from buss to ground. I dont know for sure. I am looking for other peoples expertise. See what you think from looking at the pictures.
Question. Because this is a split panel, would that mean that the six disconnect rule, would apply to the bottom and top? 2 seperate panels (services)?
This is just a shot in the dark, but it looks like the most damage is at the bottom, perhaps a stray locknut or screw or other metallic object fell between everything and just sat there un-noticed and causing no harm, until for some reason it shifted or moved around a bit and shorted across the busswork starting that whole trainwreck. one little flash, some carbon and molten metal flying around and now you might have a path for a continuous arc and LOTS of heat. Kind of like striking an arc with a stick welder is what I see happened there.
Perhaps it was a piece of mounting hardware or something off that breaker I see in one of those pictures with what looks like a missing connection... Somerthing does not look right there as only one connection is damaged on the breaker, yet all the damage was at the bottom of the panel at the back. That might have been the "start" of the "end" of that panel!
This was my picnic on Thursday. One thoery I have is that the insulator between A buss bar and the can may have been deteriorated enough that it caused the buss to direct short with the can. Notice the neutral lug completely melted off. I dont know if it is because the most heat was directly aboove this or what.
Actually I think I see two lugs melted right off the neutral buss and in the last picture I see what looks like a couple of #12's going to a lug that are now bare and look like they were sitting in a campfire. Dunno, I think the lugs ended up getting burned off from the shear heat.. What were the busses made of? Copper? Regardless if there was enough heat present to melt the busswork (especially if it was copper) and burn insulation some distance away, an aluminum lug (appears to be) will not last long in that kind of environment. Just from the jagged edges of the buss work and shear damage I think there had to be severe steady arcing and some insane amounts of heat going on. What caused it I am not sure, I still call it as some object shorted the busswork and touched off a nasty chain of events.. I don't know if I would go with the broken down insulator theory right yet. I never have seen one go bad and "Conduct" especially if it was in a nice clean and dry location.. Introduce some moisture and dirt to a cracked or damaged insultor and then thats different, I could see an insulator start to conduct in that case. BTW, What is the system voltage? I see brown? yellow and orange tape and there is a neutral present so that must be 480Y / 277V???
[This message has been edited by Rewired (edited 11-11-2006).]
Correct it is a (was) 480/277v 4wire system. Like stated by moderator from my notes, this is a split panel. Top half was for HVAC and bottom half for general loads. This is a prime example why main lug panels, using six disconnect rule, for service equipment should be outlawed.
This had to have been going on for some time. 8am secretary reported to fire alarm co., that the alarm was going off, and if they could come reset it. Alarm co. shows up, (what do you think 1/2hr?) Opens electrical room door, see's the panel glowing and calls fire dept. Fire dept shows up and wont do anything because there is no main disconnect. Leaves the scene and never returns or follows up. I show up 50minutes after initial call from secretary. POCO still not on scene. Panel completly cooked by this point obviously. POCO shows up, opens padmount xfmr (13.2kv-480/277) and opens primary switch. A and C phase primary fuses blown. What if fuses didnt blow?? Dust on the insulators for sure. This panel is 30years old, and many times this panel cover has been left off. Very dusty and dirty room too.
Off topic a bit, but you mean to tell me the secretary assumed the fire alarm was false and did not even check to see what was going on or at least get someone to investigate??!! Wow thats not too swift! I mean in that case, the fire alarm is going off, and the lights HAD to have been flickering with what was going on in the panel, something would tell you there is a problem right off the bat would it not,ESPECIALLY if someone looked at the fire alarm annunciator panel and saw an alarm originating in the electrical room.
As for that "6-disconnect" rule, that does not apply here in Canada, I think any building with more than one circuit requires a main disconnect. I could be wrong but thats how I understand it.
I also agree that that 6-disconnect" rule using MLO panels should be outlawed as from what I see, is unsafe. All that damage would not have happened and the panel would probably still be serviceable with some work if it were protected by a set of fuses or a breaker upstream. IMHO I never really liked the idea of unfused service conductors inside a building PERIOD. If I am doing a service(resi) I try as best I can to enter the building and end up right in the back of the main disconnect whenever possible.
Fire dept shows up and wont do anything because there is no main disconnect. Leaves the scene and never returns or follows up.
Good thing that the building didn't burn. The FD should not have left until the sceen was secure. The FD would have had a serious liability problem if the fire would have spread. Yes, in most cases you cannot sue the FD and win. The most notable exception is for wanton and wilful miscondut, which this was. Don added left out word in bold
[This message has been edited by resqcapt19 (edited 11-13-2006).]
I vote for a failed bonnectiom where the breaker was bolted to the bus. Take a close look at where the breaker was bolted to the bus. A bolted connection may not have been torqued sufficiently and may have started to get warm under a load. When the load is reduced the connections cools and the heats again under load. This repeating cycle loosens the connections further increasing the heating to the point where the connections starts to fail and begins to arc across itself. Increased arcing ionizes the air around the arc and involves an adjacent phase and then the neutral of ground that would be close by.