grounding on parralel feeds

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john2mcc

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when you run 4 3c 500mcm cables with a #2 ground in each cable to a 1600 amp main breaker in switchgear feeding main lugs in mcc and the cables are ran in in the same run of cable tray do you have to run a sificant ground for the full load with each cable or one ground for all 4 runs?
 

charlie b

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I think this is a problem. Since the EGC is included in each of the four cables, then each EGC must be sized for the 1600 amp OCPD. I suspect that a 500 MCM cable with a 4/0 EGC is a non-standard item, and would have to be special ordered at a very high extra cost. So my suggestions are to either use the tray as the EGC, as Pierre suggested (if your particular circumstances allow that option), or to use single conductors (not 3/c with EGC cables) in the tray.
 

tom baker

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There was a provison in the 2005 NEC that allowed a smaller EGC for cables in parallel but it appears to be deleted for the 08. It allowed the setting of the GFP relay to be based on the smaller EGC when cables were run in parallel. It is possible to order cable with oversized EGC.
 

petersonra

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Northern illinois
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engineer
when you run 4 3c 500mcm cables with a #2 ground in each cable to a 1600 amp main breaker in switchgear feeding main lugs in mcc and the cables are ran in in the same run of cable tray do you have to run a sificant ground for the full load with each cable or one ground for all 4 runs?

I agree with the rest of the posters that the EGC has to be full size in each cable if you don't use the cable tray as the EGC.

I also agree that the cable tray can be the EGC (presuming it qualifies as one).

I cannot think of any reason why you could not run the four 3/G cables, and still use the cable tray as your EGC.

As for cost, my guess is that in the sizes you are talking about, the extra cost to get a cable made up with a larger EGC is not as bad as you might think.
 
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angtomspi

New member
You'd most likely still be shocked by the pipes even if you didn't bond them. They could already be bonded via a water heater circuit. Or, if they are metal in the dirt (likely in an older house), they are grounded enough to shock you.
 

don_resqcapt19

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There was a provison in the 2005 NEC that allowed a smaller EGC for cables in parallel but it appears to be deleted for the 08. It allowed the setting of the GFP relay to be based on the smaller EGC when cables were run in parallel. It is possible to order cable with oversized EGC.
If was deleted because it called for a GFP that was listed for the purpose of protecting the EGC. There was never a GFP listed for that purpose, so even if you are still using the 2005 code you can't use that method to comply with 250.122(F).
 
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