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#165210 - 06/22/07 10:37 PM 1200 Amp with a shorted wire!!  
mr_electrician  Offline
Member
Joined: Jun 2007
Posts: 106
London, Ontario
Hello everyone. I have a quick question. I have at work a 1200 amp buss that is fed with 500 mcm cables in 3" conduit. 3 cables per phase. This install was put in about 2 years ago by a contractor. Last week one of the wires all of a sudden went to ground between the tap box and the switch gear. My only theory is that it must of been nicked during the install, and as we loaded the buss over time it finally broke down. Would anyone agree with this theory. Now I have to pull out all 3 cables of the B phase which is 190 feet, 2 90's, and 2 30 degree offsets!! Any suggestions or tricks to make this easy. I do have a pull box right before the switch gear. I am not looking forward to this!! Any advise will help. I am going to rent a tugger!!!!


Never trust an electrician with no eyebrows!!

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#165211 - 06/22/07 10:59 PM Re: 1200 Amp with a shorted wire!! [Re: mr_electrician]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
A nick is possible. A defect in the wire is possible. Degradation over time is possible.

No point in trying to fix it ... cut to the chase, and replace ALL the conductors in that pipe,


#165212 - 06/22/07 11:12 PM Re: 1200 Amp with a shorted wire!! [Re: renosteinke]  
twh  Offline
Member
Joined: Mar 2004
Posts: 903
Regina, Sask.
Pull out all three cables of the B phase? Hopefully, they're not in the same conduit.

Anyway, if a conductor is pressed very hard against a wall of a box or edge of a conduit, it can compress the insulation to the point of failure.

My advice for the pull is to use lots of lube and get lots of help.


#165213 - 06/22/07 11:32 PM Re: 1200 Amp with a shorted wire!! [Re: twh]  
Theelectrikid  Offline
Member
Joined: Apr 2004
Posts: 810
Levittown, PA
Hmm, maybe Scott/Electure can lend 'ya an elephant. laugh wink

Ian A.


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#165220 - 06/23/07 08:34 AM Re: 1200 Amp with a shorted wire!! [Re: mr_electrician]  
togol  Offline
Member
Joined: Sep 2005
Posts: 421
NW In. USA
B phase is bad? are you just saying that the center pipe is the problem ?.
..if this is in the slab pour some lube into the pipe at both ends..then pull only one cable at a time. pick a cable, serve on a clove hitch and several half hitches close to the pipe take the free end of the cable and make a loop in it to keep the rope from flying off..now the hard part.

someone will have to make sure the now looped cable stays looped, use an open, gloved, hand to do this, slowly put pressure on the pulling rope with the tugger, release the pressure, re-apply pressure, release ..until the cable starts to move..keep the loop closed..DO NOT STAND in front of the rope.be sure you are to the side ..pull the cable out as straight as possible. make sure that everyone involved is on the same page !

You may only need to rig the tugger once, after the first cable is out the others might just come out by hand


Tom

#165261 - 06/24/07 09:12 AM Re: 1200 Amp with a shorted wire!! [Re: togol]  
mr_electrician  Offline
Member
Joined: Jun 2007
Posts: 106
London, Ontario
No, what I mean is the B phase in one of the pipes is shorted. I will have to pull all 3 cables out of the EMT.


Never trust an electrician with no eyebrows!!

#165263 - 06/24/07 10:34 AM Re: 1200 Amp with a shorted wire!! [Re: mr_electrician]  
togol  Offline
Member
Joined: Sep 2005
Posts: 421
NW In. USA
Ok. so this run is above grade
try to put as much lube on the first wire you pull out, years ago we would use Ivory Snowflakes and a bit of water, but now that's frowned on


Tom


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