Commercial Service Grounding

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mjc

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Hi guys,
We are installing a Meter module center outdoors on the back of a commercial building. This center will have three sections: section #1 is an 800amp main (not switch) to be fed with parallel 500mcm conductors, section # 2 has 3 meters and a 200amp circuit breaker each, section #3 has 2 meters and a 200a circuit breaker each. 3/0 conductors will originate at each 200amp CB. Travel underground through pvc then up to an LB on the wall, go into the build and terminate in a 42ckt MLO panel.

Am I reading ex. 2 of 250.142B correctly in that I dont have to include an equipment ground with these with the 3/0 because the Grounded (or nuetral)conductor is acceptable to the NEC even though the raceway is PVC ? (I would have separated the the grounded conductors and grounding conductor not to have parallel grounded conductors at the panel.
ALSO
How do I read table 250.66 in Order to provide a GEC for parallel 500MCM conductors. It talks about equivalent size? :confused:

Thanks for the help, Mike
 
Re: Commercial Service Grounding

Am I reading ex. 2 of 250.142B correctly in that I dont have to include an equipment ground with these with the 3/0...?
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I don't believe you are. This exception is for the meter enclosures at the service equipment, not the panels downstream.

Quick question: Are you running underground to a different building, or back to the same building?

How do I read table 250.66 in Order to provide a GEC for parallel 500MCM conductors. It talks about equivalent size? :confused:
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I'm not quite sure which "equivalent size" you're referring to, Note 1 or 2. In a quick read, I didn't think either applied to your installation.

The equivalent size of two sets of copper 500 MCM conductors is 1000 MCM. You'd need a 2/0 CU, (or 4/0 AL, if preferred, so long as it's terminated farther than 18" from the earth).

[ February 28, 2006, 11:39 PM: Message edited by: georgestolz ]
 
Re: Commercial Service Grounding

Sounds to me, if I'm understanding your installation, that your main service disconnect is on the outside of the building. Any MLO panel after that, within the same building, would become a subpanel and would require a grounded and grounding conductor in the feeder.

As George mentioned the equivalent size would be for parallel conductors. In this case the 2-500kcmils would be the equivalent of 1000kcmil which would be used for sizing your GEC.
 
Re: Commercial Service Grounding

Good Morning,

Quick question: Are you running underground to a different building, or back to the same building?
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Answer to this Question would be the same building.

George --
Reading 250.142 B ex.2 to fast , I was missing the point "meter enclosures" Thanks for the heads-up


Trevor/George table 250.66 is much clearer thats what I ASSumed (Parallel 500 MCM would be equiv. to 1000 MCM) but was affraid of those first three letters.

Thanks for the help! Mike :D
 
Re: Commercial Service Grounding

Originally posted by mjc:
Am I reading ex. 2 of 250.142B correctly in that I dont have to include an equipment ground with these with the 3/0 because the Grounded (or nuetral)conductor is acceptable to the NEC even though the raceway is PVC ?
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After the service disconnects, you size your feeder EGCs per table 250.122. And no, they can't be omitted as the others have said.

[ March 01, 2006, 11:23 AM: Message edited by: peter d ]
 
Re: Commercial Service Grounding

Originally posted by infinity:

Who said that they could be omitted?
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Nobody. I should have said this: "The others are correct in stating that the EGC cannot be omitted."

Does that make sense now?
 
Re: Commercial Service Grounding

Bond all enclosures together per 250.122. Install 1 grounded conductor based upon the size of conductor going to the sub-panel per 250.66 or equal to the size of the ungrounded conductors. Install an equip. gnd also per 250.122
 
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