power company mistake causes major damage!

[charlie tuna]

today i was called to a site where an electrician was burnt-eye-arms-hands-head. he was working in an energized 1200 amp-480/277 volt distribution panel and apparently shorted something out! the 1200 amp panel was melted! the panel was fed from a power company vault directly behind the panel. the 600mcm cu service wires were burnt back into the vault! why so much damage i asked myself??? the fire department released the inside of the vault and allowed us in. i found the problem quickly. the power company wiring was wrong! the neutral conductor off the power company's transformer connected to a long copper bus that had nothing connected to it? a second(shorter) copper "ground bus" had the customer's neutrals connected to it-this "ground bus" had one #1/0 run to the vault ground loop and another #1/0 run to the neutral bus bar. both of these conductors were burnt in half. the power company's transformer never seen any fault current via the neutral and seen the problem as a load!

 

[hurk27]

Re: power company mistake causes major damage!

I think this electrican should not have been in a live panel without the proper PPE's or should not been in the panel at all unless it was shut down. But I'm not following somthing or something just dont sound right? 600mcm on a 1200 amp service? if the neutral was only 1/0 why did the 600mcm go? most POCO transformers are not protected on the secondary side of the transformer. Was there a main breaker/fuses and GFP? should have been as per:215.10?????

[ July 15, 2004, 01:52 AM: Message edited by: hurk27 ]

 

[charlie]

Re: power company mistake causes major damage!

If the 480Y/277 volt bus had nothing attached to it, perhaps this was an installation where the neutral was not used as a circuit conductor. If that was the case, this effectively became a 480 volt delta service. Check out 250.20(B)(1) & (2). I would also request you check with the electric utility to see what their standards are and what service was supplied.

If this was supplied as an ungrounded delta, it sounds like it was done correctly. If this was a wye service, did meet 230.95?

 

[charlie tuna]

Re: power company mistake causes major damage!

this was not a 480 volt delta service--it was 480/277 - 3 phase - 4 wire.
whoever wired the vault mistakenly installed the customer's neutral conductors on the vaults ground bus. this ground bus was connected to the vault's groung loop by a 1/0 (cu)?(al)? and onother jumper the same size to the "real " neutral bus which was connected to the neutral terminal of the transformer by a 750 mcm al. when these two 1/0 jumpers blew apart there was no current path between the transformer neutral and the customer's neutral. the service wires burnt back into the vault melting the four inch rigid nipples in the vault wall. when the fire department got on site the pothead out on the street pole was on fire--the power company guy said the primary fuse was 200 amps!!!

 

[charlie]

Re: power company mistake causes major damage!

What happened to the ground fault protection? Have you talked to the electric utility?
Have you looked at my previous references?

 

[bob]

Re: power company mistake causes major damage!

Charlie T
It sounds like the contractor is the one who made the mistake. The code resuires that the grounded conductor be brought to the main switch even if it is not being used. The utility installed the neutral to the ground bus. Its the contractors job to see that it is brought to the main. It appears that maybe a jumper should have been installed to connect the utility ground bus to the customers ground bus.

[ July 15, 2004, 01:22 PM: Message edited by: bob ]

 

[hornetd]

Re: power company mistake causes major damage!

Originally posted by bob:
Charlie T
It sounds like the contractor is the one who made the mistake. The code requires that the grounded conductor be brought to the main switch even if it is not being used. The utility installed the neutral to the ground bus. Its the contractors job to see that it is brought to the main. It appears that maybe a jumper should have been installed to connect the utility ground bus to the customers ground bus.

I'm not trying to be quarrelsome when I say that all work in the vault is done by the utility's outside wiremen in every area I have worked in. Could the electrical contractors inside wiremen have done any work in the vault in the area in question.
--
Tom H

 

[charlie tuna]

Re: power company mistake causes major damage!

the next day i met the actual guy(contractor) who got burnt. said he had the panel cover off and was confirming phasing of an abandon four wire feeder. he said "i set my cell phone (nextel) on the top of a breaker(inside the panel) and shut off the 1200 amp main". it blew up right then. i asked why he put the cell phone in the panel and he told me so the man he was working with on the other end of the feeder could communicate with him since he was using both hands to check the phasing... thank god he's gonna be ok!!! but he is really hurtin! he wanted to do the repair--i thought--hay, this guy has some guts!!! well i transfered my emergency parts order at my supplier to his account--no problem! then the power company representative showed up and he asked if we wanted to see the inside of the vault. he also said they had disconnected all the customer cable connections. when i looked--they had installed two 600 mcm copper jumpers between the ground bus and the neutral bus--you could see by the fresh scratch marks on the ground bus that they were just installed! the other contractor asked about the jumpers and the power company's representative got "huffy" and said "those were always there". his attitude got the best of me--i told him otherwise!!!!!!!!!!! i have e-mail capable photos of the situation.

 

[charlie tuna]

Re: power company mistake causes major damage!

re: power company's ground fault sensor?
don't think it could see anything but load after the two jumpers(one 1/0 al to the neutral bus and one 1/0 al to the vault's ground loop) blew in half. at that point the six service wires (parallel 600 mcm cu) were electrically wrapped together in a fire ball. i think at that point the power company's system was thinking it was just a load? people on site said that it just kept exploding for about ten to fifteen minutes until it burn something up in a manhole down the street? the electric room has a glassed riser area that is open to the second floor and they could see the flashes corresponding to the explosions and thought the windows were gonna blow out! my opinion---when you see this much damage and meltdown ---- some overcurrent device was wrong or did't function! another job i saw recently was a bus duct failure. there was three feet of a 2000 amp bus duct "missing". why "i asked myself"? why didn't blow the 2000 amp fuse at the main? i could understand the problem blowing a hole in the side of the bus duct-- i've seen that enough. but when you see three feet missing---it burnt for "some time"!!! in this case the switchgear manufacturer(square d) made a mistake in manufacturing---in one area two "b" phase buses were passing each other--"almost" touching each other---someone in the factory installed a piece of fishpaper between them figuring "hay they are both "b"phase? but one was line from the vault and the other was from the load side of the main switch. when the bus duct failed on the ninth floor of an office building the flash from the original problem(water from a roof leak) exited the electrical closet through the door (fire rated) frame and set off a fire sprinkler 18 inches away and blew all the fuses. the water ran down the core area of the building and into the switchgear directly nine floors below. water got on the fish paper and blew through (now there was a 277 volt potential between these "b" phase buses) and connected the power company's "b" phase vault directly to the bus duct fault. thats what burn away three feet of bus duct! the insurance investigators never caught on to the problem. remember when you see sever damage and meltdown--look closely to all over current devices--my own opinion.....

 

[charlie]

Re: power company mistake causes major damage!

Our downtown network in Indianapolis is 208Y/120 volts and we have some spot networks where we have multiple transformers. For the most part, where the voltage is 480Y/277, we are serving it with a single transformer. In this case (or cases), I am assuming that this is a spot network with several transformers feeding the same bus.

When you have a situation like that, you have a tremendous amount of fault current available and need to follow 230.95. Additionally, cable limiters should have been installed although they are not required by the NEC. FWIW, we require them in the downtown area because of the extreme amounts of fault current available.

 

[charlie tuna]

Re: power company mistake causes major damage!

another thing that i just thought of---the 1200 amp panel was connected to a generator transfer switch via a 2 1/2" emt raceway. all the diecast fittings were gone--melted even though they were away from the flash and meltdown area. this means the fault current must have been carried through this raceway back to the generators ground system until all the fittings disappeared?

 

[charlie tuna]

Re: power company mistake causes major damage!

an update on this neutral miswire! i was called to the site by the original contractor to restore wiring to critical building operations. after this work was complete the chief engineer of the college asked us to look at a room with four out of ten 2 x 4 light fixtures not working? the first fixture had a blown fuse??? we replaced the fuse and it blew soon as it was installed! electronic ballasted 277 volt fixtures--about two years old? we then looked at the layout of the fixtures that were out. it looked to us as though they were night lights powered from the emergency distribution panel. we then began looking at other rooms--about half of the emergency fixtures had blown ballasts! the ground bus in the power company's vault is located within three feet of the area where the phase conductors burnt back into the vault--it is probible that after the small cables connecting the ground bus to the heavy neutral bus were blown in half-this isolating the service neutral conductors which were mis-connected to the ground bus--got energized by the large fire ball electrical exposions produced by the vault transformer. this could cause voltages up to 480 volts to be seen by emergency circuits? we also ran into the building management contractor who had found many vav boxes not functioning? they were also connected to emergency circuits because they are used in smoke evacuation sequencing. many of the control cards were smoked? i hope something is learnt from this mistake?? but its been my expieriance that the insurance company does not have the knowledge to figure everything out!