Parallel conductors and GEC 2005 code cycle

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acrwc10

acrwc10

Master Code Professional
Location
CA
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Building inspector
I am running a feeder from a pad mounted switchgear with a 500 amp main breaker in the gear using 3 parallel runs of 4/0 AL conductors, 250' into the house, where they will terminate into a distribution block. Using the inside tap rule I am planning to run to four 200 amp distribution panels grouped (230.71A) each with a 200 amp main breaker intalled.
Under the 2005 NEC I am not required to run a ground with the feeders from the switch gear to the house, I just need to bond the Ground Electrode Conductor and the feeder neutral at the service disconnects at the house.
Since I am using four 200 amp main disconnects, grouped in the same room, do I size my GEC (table 250.66) for the individual disconnects (#4 cu) or size it based on the three parallel 4/0 and bond it at the distribution block.
 
Art. 250.32(B)(2) allows you to run a 3 wire cable as long as there are no metallic pathways between the building. IMO, run the egc because the new codes require it. Now if you don't run the egc then everything gets bonded together but if you do run it then the neutral gets isolated and the GEC gets connected to the equipment ground bar.

Now if you size the egc then it must be sized to the 500 amp breaker and it must be with each run of parallel conductors.

The GEC can be run from each individual panel or you can size it on the sum of the service conductors and run it to the distribution block.
 
Dennis Alwon said:
Art. 250.32(B)(2) allows you to run a 3 wire cable as long as there are no metallic pathways between the building. IMO, run the egc because the new codes require it. Now if you don't run the egc then everything gets bonded together but if you do run it then the neutral gets isolated and the GEC gets connected to the equipment ground bar.

Now if you size the egc then it must be sized to the 500 amp breaker and it must be with each run of parallel conductors.

The GEC can be run from each individual panel or you can size it on the sum of the service conductors and run it to the distribution block.
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The feeders are in PVC, I am not running an EGC with the feeders because the only thing at the switch gear will be a ground rod. So putting an additional 1/0 AL in each conduit seems like a big waist of money.

What I am wondering is, am I required to size my ground earth conductor for the 3 parallel runs of 4/0, Or may I size it for the individual panels. The same as if you had 4 panels on an aptment house.
 
acrwc10 said:
The feeders are in PVC, I am not running an EGC with the feeders because the only thing at the switch gear will be a ground rod. So putting an additional 1/0 AL in each conduit seems like a big waist of money.

What I am wondering is, am I required to size my ground earth conductor for the 3 parallel runs of 4/0, Or may I size it for the individual panels. The same as if you had 4 panels on an aptment house.
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GEC requirements, with the exception of bonding to grounded conductor, are the same as if a service were run to the building. All are sized per 250.66. With multiple disconnects a Common GEC must be sized based on feeder size. Individual GEC's (i.e. one for each panel) or GEC taps to a Common GEC can be sized based on the feeder tap size.
 
Smart $ said:
GEC requirements, with the exception of bonding to grounded conductor, are the same as if a service were run to the building. All are sized per 250.66. With multiple disconnects a Common GEC must be sized based on feeder size. Individual GEC's (i.e. one for each panel) or GEC taps to a Common GEC can be sized based on the feeder tap size.
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That is what I was thinking, I just wanted to be sure I wasn't missing something.
 
This is not answering your question but the tap conductors feeding the 200 amp panels must be protected at or below their ampacity. You will need to use 250 AL conductors for the 200 amp breakers. Maybe you are already planning to do this but since you mentioned 4/0 for the 500 amp feeder I just thought I would bring it up.

I personally would never do this install without installing an EGC between the service equipment and the panels.
 
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acrwc10 said:
What I am wondering is, am I required to size my ground earth conductor for the 3 parallel runs of 4/0, Or may I size it for the individual panels. The same as if you had 4 panels on an aptment house.
Click to expand...
I thought I answered that in the last sentence of my post.

The GEC can be run from each individual panel or you can size it on the sum of the service conductors and run it to the distribution block.
Click to expand...

I see I didn't state that the GEC from each panel, if you choose to do it that way, may be sized based on the conductors to that particular panel.
 
curt swartz said:
This is not answering your question but the tap conductors feeding the 200 amp panels must be protected at or below their ampacity. You will need to use 250 AL conductors for the 200 amp breakers. Maybe you are already planning to do this but since you mentioned 4/0 for the 500 amp feeder I just thought I would bring it up.

I personally would never do this install without installing an EGC between the service equipment and the panels.
Click to expand...

Yes we will use 250 AL, good call though, seeing as you can run a 4/0 for a single 200amp service (as long as the load isn't over 180 amp) it could have been an easy over sight,
 
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