Grounding Electrode Conductor Size for Dual Services

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stevero

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I am upgrading my service to a dual meter service - one for the general house service,and the other for electric heating which is billed at a separate rate. Using my local utility's standards, I will set a new 400-amp meter socket with new weather head and 500 kcmil cu conductors to the service side of the meter. I will jumper between the service-side lugs on the new meter socket to the service-side lugs on the existing 200-amp meter socket with 2/0 cu conductors. Each meter socket will connect to separate 200-amp load centers with 2/0 cu conductors.

My local permitting agency says I need 1/0 cu ground electrode conductor (for 400 amp service). I say I need #4 conductor for 200 amp service. It seems to me any ground fault would be cleared by a 200-amp main breaker, therefor sizing for 200 amps should apply.

Who's right? (BTW, I will run the GEC from ground to one panel, and then jumper to the second panel - 16 inches away.)
 
Re: Grounding Electrode Conductor Size for Dual Services

1st tell us what the electrode is?

If it is a metal water pipe, then you can run a common 1/0 GEC from the water pipe and tap a #4 to each 200 amp disconnect...or run a seperate #4(two continuous runs) from each disconnect to the waterpipe...250.64(D)

see exhibit 250.26 2002NEC handbook for example...

shortcircuit2
 
Re: Grounding Electrode Conductor Size for Dual Services

The water pipe is my primary ground. Also have a ground rod.

As I understand the code, the GEC must be unspliced. Won't the idea to tap two #4 wires from the 1/0 violate this? I'd rather take #4 wire to the panels, as I don't think my ground lugs are big enough for 1/0. Maybe the best is to run dual #4 wires as you suggested.
 
Re: Grounding Electrode Conductor Size for Dual Services

stevero...2 ground rods a minimum of 6 feet apart to supplement a water pipe unless the 1st is 25ohms or less.

Did you look at the example in the 2002NEC?

The 1/0 can stop, lets say above the two 200 amp panels and then tap a #4 (with burndies for example) into each panel.

shortcircuit2
 
Re: Grounding Electrode Conductor Size for Dual Services

Originally posted by stevero:
...I will set a new 400-amp meter socket with new weather head and 500 kcmil cu conductors to the service side of the meter.
...It seems to me any ground fault would be cleared by a 200-amp main breaker, therefor sizing for 200 amps should apply.
Click to expand...
See Table 250.66. You need a 1/? CU water bond. It's based on the size of the ungrounded conductors feeding your service, not the ampacity of any breaker you install.

Edit to add: I'm confused at why this is being made tricky with the inclusion of #4--if the two disconnects are 16" apart, why not just loop through one and hit the second with the 1/?? :confused:

Edited again: If there is an existing drop, and you're adding a drop, why not just size the second drop for 200 amps, and forget about it? :confused: :confused:

[ March 05, 2005, 08:58 AM: Message edited by: georgestolz ]
 
Re: Grounding Electrode Conductor Size for Dual Services

Originally posted by stevero:

My local permitting agency says I need 1/0 cu ground electrode conductor (for 400 amp service). I say I need #4 conductor for 200 amp service. It seems to me any ground fault would be cleared by a 200-amp main breaker, therefor sizing for 200 amps should apply.
Click to expand...
The GEC is not part of the fault clearing path, so this logic does not apply. The size of the GEC is based on the size of the incoming conductors.
 
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