Parallel Grounds

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Mike01

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Can someone explain how to size grounds for parallel conductors for a SDS I still cannot understand how this is accomplished. Ex. 1600A feeder 4 sets parallel 600?s. so the total cmill area is 1680cmills. 12.5% of that is 210cmills that would mean a 4/0 would be required as my ground. But 250.30(8)(b) states the size of the ground conductor in each raceway shall be based on the ungrounded conductors in the raceway but not smaller than 1/0, so does this mean 12.5% of a single 600 as that is the largest phase conductor in that conduit? If you had a 3000A service with 7-sets of 600?s 12.5% would be 525000 that would mean a 600kcmil grd. In each conduit? Is that correct or would it be 12.5% of a single 600 in that case a 1/0 would be fine as the min. size allowed to be paralleled??:confused:
 
Are you asking about the secondary conductors?

The GEC is sized according to the secondary conductor size listed in 250.66.

The bonding jumper from the XO to the case is sized according to 250.66 or 12.5% if the secondary conductors exceed the conductor size in 250.66.

Each parallel raceway will get a bonding jumper sized according to the conductors within that raceway. Look at 250.102(C).
 
Mike01 said:
Can someone explain how to size grounds for parallel conductors for a SDS I still cannot understand how this is accomplished. Ex. 1600A feeder 4 sets parallel 600?s. so the total cmill area is 1680cmills. 12.5% of that is 210cmills that would mean a 4/0 would be required as my ground. But 250.30(8)(b) states the size of the ground conductor in each raceway shall be based on the ungrounded conductors in the raceway but not smaller than 1/0, so does this mean 12.5% of a single 600 as that is the largest phase conductor in that conduit? If you had a 3000A service with 7-sets of 600?s 12.5% would be 525000 that would mean a 600kcmil grd. In each conduit? Is that correct or would it be 12.5% of a single 600 in that case a 1/0 would be fine as the min. size allowed to be paralleled??:confused:


Some further information from your post:

4 set of 600 kcmil= 2400 kcmils not 1680

2400 * 12.5% = 300 kcmil

The bonding jumpers in each parallel raceway are sized according to 250.30(A)(2) which sends you to 250.102(C).
 
If the parallel conductors are protected by a 1600A OCD, then you must run a 4/0 EGC in each raceway. (NEC 250.122(F))
 
jbt260 said:
If the parallel conductors are protected by a 1600A OCD, then you must run a 4/0 EGC in each raceway. (NEC 250.122(F))

He said that this was an SDS so there would no OCPD ahead of the 4 sets of 600's.
 
Bad Math

Bad Math

Sorry for the confusion my math was off I said 600?s but was thinking of another wire size. Let?s try this again:

Utility owned transformer 2000A service 5-sets or 600kcmil?s (5*600,000 = 3,000,000cmills @ 12.5% = 375,000cmills) so this means I would need to run a 400Kcmil min. size grounded service conductor with the phase conductors. So I would end up running 5 conduits each with 3#600kcmil&1#400kcmil ground or,

The last sentenance or 250.102(C) states ?The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.?

Does this mean that it is sized based on 12.5% of a single 600 (the size of the service-entrance conductor in one of the paralleled conduits.

Running the conduits from the utility xfmr to the sw.gear you would only have the three phase conductors and the grounded conductor run in parallel.

Does this sound correct?
 
Mike01 said:
Utility owned transformer 2000A service 5-sets or 600kcmil?s (5*600,000 = 3,000,000cmills @ 12.5% = 375,000cmills) so this means I would need to run a 400Kcmil min. size grounded service conductor with the phase conductors. So I would end up running 5 conduits each with 3#600kcmil&1#400kcmil ground or,

You would run (3) 600 kcmil phase conductors,(1) 400 kcmil (minimum)grounded(neutral) conductor.No grounding conductor required (service).
Mike01 said:
The last sentenance or 250.102(C) states ?The size of the bonding jumper for each raceway or cable shall be based on the size of the service-entrance conductors in each raceway or cable.?

With this being service conductors, there isn't going to be a (system)bonding jumper with each raceway, only the grounded conductor.

If this was a feeder from a SDS down stream of the service, you could run a system bonding jumper in each of the raceways, and that would be sized on the conductors in each of the raceways, not the total of all the conductors.
Mike01 said:
Running the conduits from the utility xfmr to the sw.gear you would only have the three phase conductors and the grounded conductor run in parallel.

Does this sound correct?
Yes that is correct.
 
System bonding jumper for a SDS(we called the main bonding jumper a few years ago) is different than the equipment bonding jumper, which is required to be ran with the phase conductors in each raceway to the first disconnecting means of the SDS. Sized per 250.66 for conductors in each raceway. The system bonding jumper is sized using 250.66 and the total cmil area of conductors applying the 12.5% if needed.
 
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