3 breaker panels / 1 GEC ?

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richwaskowitz

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Shelby Twp. MI, near Detroit
When one has three 100 amp panels (grouped together at one location) for three apartments from one service drop, one grounding electrode conductor and one supplemental grounding conductor, how does one properly connect those grounds to the three panels?

1. Is #4 or #6 GEC required? (since the drop is 200 amp (4/0 Al) but the individual panels are 100 amp (#2 Al))
2. Is tapping off the #6 or #4 bare with split bolts acceptable?
 
Re: 3 breaker panels / 1 GEC ?

1. Common GEC = min. # 4 AWG per 250.66.
Bonding Jumpers = min. # 8 AWG per 250.66

2. If listed per 250.8
 
Re: 3 breaker panels / 1 GEC ?

The answer to #2 is found in 250.64(D).
The GEC is sized per the size of the service entrance conductor, the GEC taps are sized per the size of the phase conductors to the individual panels, and the last sentence says the taps have to be connected without splice - so an irreversible connection is required.
Remember that the taps are still GECs and have to remain unspliced or spliced by irreversible means.
So your split bolt method is not permitted.

Pierre
 
Re: 3 breaker panels / 1 GEC ?

Pierre I disagree.

The taps are not the GEC and the taps can be connected to the GEC with split bolts, the GEC remains continuous.

If the NEC intended what you describe IMO they would say:

"The GEC taps shall be only by irreversible compression-type connectors listed for the purpose or by the exothermic welding process."
 
Re: 3 breaker panels / 1 GEC ?

Pierre, personally I disagree, I believe code permits the use, but give you credit in your interpretation. ;) If it were me I would run a the # 4 AWG GEC to the furthest service panel neutral, and "H" tap a # 8 for the two closest panels. IMO any mechanical splice will fail in a short period of time like the one on the water pipe or ground rod. :eek:

Don Res, what is your opinion?

[ July 21, 2004, 12:04 AM: Message edited by: dereckbc ]
 
Re: 3 breaker panels / 1 GEC ?

This type of response is the reason I like this type of forum, we can ferret out the answer to a question that may be difficult to understand or interpret.
Here is how I read this:

"250.64(C) Continuous. The grounding electrode conductor shall be installed in one continuous lenth without a splice or joint, unless spliced only by irreversible compression-type connectors listed for the purpose or by the exothermic welding process."
(qoute from 2002 NEC)

I think we can all agree that the NEC requires the GEC to be continuous and unspliced unless if spliced by irreversible means.

"250.64(D) Grounding Electrode Conductor Taps.
Where a service consists of more than a single enclosure as permitted in 230.40, Exception N0 2, it shall be permitted to connect taps to the grounding electrode conductor.Each such tap conductor shall extend to the inside of each such enclosure. The grounding electrode conductor shall be sized in accordance with 250.66, but the tap conductors shall be permitted to be sized in accordance with the grounding electrode conductors specified in 250.66 for the largest conductor serving the respective enclosures. "

This last sentence is where I interpret the connection of the taps has to be of an irreversible form.

" The tap conductors shall be connected to the grounding electrode conductor in such a manner that the grounding electrode conductor remains WITHOUT A SPLICE. "

To me this says the same as irreversible splice.

splice
 
Re: 3 breaker panels / 1 GEC ?

Here's how we do it:

#6cu. from each panel to the round rod.(use 3 acorn clamps)

#4cu. from the farthest panel to the waterline.

#6cu.(#8 is what the table says, but we don't stock it) from each of the other two panels to the #4 and use a split bolt on each tap.

We have done this type of service this way many times. I hope the interpretation was correct.
I agree with Bob's theory on the wording as he pointed out above.
 
Re: 3 breaker panels / 1 GEC ?

I apreciate all the replies, but I think Lukewarmwater confirmed my original thought wherein he points out that tapping off of the one #4 GEC with two #6's (or #8's if so desired) using common splitbolts will allow the GEC to remain in one piece and unspliced. The splitbolts could not possibly be any lesser of a mechanical connection than the groundrod clamp or the pipe clamp at the watermeter.....

I will now run this by the local AHJ.
 
Re: 3 breaker panels / 1 GEC ?

pierre,

I agree with dereckbc and iwire on the split bolt question. I think that the last sentence prohibits the connection being made in any way that would involve cutting the GEC. A split bolt can be used to make the tap connection without cutting the GEC. Even an irreversible splice is a splice and the last sentence prohibits any splice, but only in the GEC itself. I believe that a connection method that involved cutting the GEC and splicing, even with irreversible means would be prohibited here. JMO :)
 
Re: 3 breaker panels / 1 GEC ?

Pierre,
The words in question are only saying the the "main" GEC cannot be cut, they are not saying that the taps have to be made with an irreversible type of connection. I see no code violation using the split bolts.
Don
 
Re: 3 breaker panels / 1 GEC ?

There is another place where grounding electrode conductor taps are referenced in the NEC. That is in 250.30 Grounding Separately Derived Alternating-Current Systems.

Here in this section there is no question the taps must be made with irreversible connections

250.30(A)(3)(3) Grounding Electrode Conductor Taps

(b)Connections. All connections shall be made at an accessible location by an irreversible compression connector listed for the purpose, listed connections to copper busbars not less than 6 mm ? 50 mm (1/4 in. ? 2 in.), or by the exothermic welding process. The tap conductors shall be connected to the common grounding electrode conductor as specified in 250.30(A)(2)(b) in such a manner that the common grounding electrode conductor remains without a splice or joint.
Click to expand...
We still have the same last sentence but the beginning is clear that the taps can not be made with split bolts.

My point in posting this other section is to show that the CMPs know how to say what they want. :)

I do not think we should read more into the code than is really there.

Bob

[ July 21, 2004, 06:01 PM: Message edited by: iwire ]
 
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