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Re: Will this installation get "Red Hot" soon? [Re: BigJohn] #182549 12/01/08 05:20 PM
Joined: Jun 2004
Posts: 1,273
T
Tesla Offline
Member
Each ground wire must be able to handle the full OCPD.

The reason is that in the event of a short in one of the pipes... ALL of the fault current floods the short, which is going to be huge. The grounding conductor in the undamaged pipe has to be able to handle the surge.

Example, a forklift or crane loses a heavy load that crushes surface mounted pipes in parallel... earthquakes... vehicle strikes... errant backhoes... subsidence crushes pipes... landslides...

If something can go wrong, it will. The instantaneous fault energy that is released from a paralleled XFMR faulting is truly astounding.



Tesla
2017 / 2014 NEC & Related Books and Study Guides
Re: Will this installation get "Red Hot" soon? [Re: resqcapt19] #184604 02/14/09 12:08 AM
Joined: Mar 2008
Posts: 27
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gpsparky Offline
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Reminds me of a hoist that we repaired once...two phases in one conduit third phase and neutral in another, only the neutral and the lone phase conduit took another route and was substantially longer to boot.

Just because it looks neat doesn't always mean it's right.


Sometimes not getting what you want can be an incredible stroke of luck.
Re: Will this installation get "Red Hot" soon? [Re: gpsparky] #184610 02/14/09 12:58 AM
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Posts: 849
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Yoopersup Offline
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Overcurrent Protection:
240.4(B) 800Amps or less next highest breaker. .
240.4(C) over 800 amps next lowest breaker.
Thus Parallel 500 mcm 380x2 = 760 next highest 800.
800 amp breaker per code.
Thus 4 sets of Parallel 500 MCM = 380 x 4 =1520.
240.6 standard breaker rateings next lowest 1200 .
1200 amp breaker per code.
4 sets 600mcm . 600mcm = 420x4=1680 . next lowest breaker 1600.
1600 amp breaker per code.
When you parallel MC cable above 800 amp you have to either order special cable(larger equipment ground) to comply with the code.
Equipment Ground in EACH conduit per 250.122F
Sized per breaker. As stated in pervious post.

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