Line Side or load side

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Ben Trueblood

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I have a service where the disconnecting means is on the first floor and I have parallel feeders going up to tap boxes that feed meter banks in a mid-rise condo building ( parallel 500 MCM AL ) The question is how to size the equipment bonding jumpers running in the individual conduits. Do they fall under table 250-66 or 250-122 table or another code article?
 
Assuming there is overcurrent protection for the service conductors on the first floor adjacent to the service disconnecting means, conductors downstream (up to the second floor) should have an equipment grounding conductor sized according to 250.122
 
So if my overcurrent protection device is 1200 Amp and I have 4 sets of 500 MCM copper then according to the table i would run 250 MCM ground. Is that correct?
 
On my last reply I meant 500 MCM Aluminum copper as the parallel conductors. It seems like overkill for the ground. Can someone explain why?
 
I agree with the 250 MCM aluminum (or copper-clad aluminum) as the EGC size. I also agree that you need the 250 EGC in each of the four parallel conduits.

I believe the reason for putting a full-sized EGC in each conduit has to do with the possibility of a short circuit being caused by something happening inside one of the conduits. All of the fault current that a 1200 OCP would permit to flow, for however long it would continue to flow, would flow through the one EGC located in that same conduit. So you need an EGC that is large enough to handle that fault current.
 
Rick,

Would you believe that Math was easy for me!! No really it was!! Just not

today I guess.

Ben,

Sorry I questioned your calc. , Luckily, I just missed my head when I sat

down!!
 
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