Satelite Structures Grounding Question

Fred wrote:

250.32 Buildings or Structures Supplied by Feeder(s) or Branch Circuit(s). (A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with 250.50. The grounding electrode conductor( s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed. Exception: A grounding electrode shall not be required where only a single branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the conductive non- current-carrying parts of equipment. For the purpose of this section, a multiwire branch circuit shall be considered as a single branch circuit. (B) Grounded Systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either 250.32(B)(1) or (B)(2). (1) Equipment Grounding Conductor. An equipment grounding conductor as described in 250.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s). (2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in each building or structure involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of either of the following: (1) That required by 220.61 (2) That required by 250.122 (C) Ungrounded Systems. The grounding

250.32(B)(2)will be gone in 2008

If I'm reading this correctly...a separate ground rod would not be required if a grounding conductor is run from the main service box to the sub service box? The grounding conductor in an approved cable would probably be sufficient?

If you are installing a sub panel (not a single circuit) you need a ground electrode system in the remote building

OK.

And would the "sub panel" we wired as such with NEUTRAL and GROUND separated?

Fred wrote:

You are not reading it right. If more than one branch circuit supplies the building then a grounding electrode system is required at the building that is supplied. It does not matter whether the feeder has an Equipment Grounding Conductor run with it or not.

Is there a definition of "one branch circuit" i.e. voltage, amps, KW?

Fred

I suspect the intent was a feeder supplying more that one branch circuit in the building. If it is a feeder, a grounding electrode is required.

From gfretwell's code section - 250.332-C-Exception - if a single branch circuit (including a multiwire branch circuit) with a ground wire is run, no grounding electode is required. Example: you run 2 hots, a neutral and a ground where the hots are from opposite service panel legs. All protected at the source at 20 amps and running 15 and 20 amp receptacles/lights in the separate building. No grounding electrode is required.

A single circuit at 30 amps to run a welder would be a single branch circuit, but then there would be no lights or 15/20 amp receptacles and would IIRC run afoul of other NEC requirements.

If 2 branch circuits - hot-neutral, hot-neutral - are run a grounding electrode is required.

bud--

Isn't it obvious? [I have seen electricians argue over this section.]

The are 2 options for feeders:

1. Include a separate ground. The supplied ground connects to ground bar along with the grounding electrode at the building panel. The neutral is insulated.

1. No ground wire is run. The supplied neutral is bonded to ground at the separate building panel and is connected to the grounding electrode at the building. (Same as a service.) There can be no other metalic connections between buildings (like metal gas line). Gfretwell says this option is disappearing from the 2008 code.

bud--

Actually from electrician's code section.

bud--

[Sorry if this post is repeated.]

I suspect Tom's intent is a feeder supplying more than one branch circuit at the separate building. Feeders always require a grounding electrode at the separate building.

From electrician's code section 250.32-C-Exception - if a single branch circuit (including a multiwire branch circuit) is run and it includes a ground wire, no grounding electrode is required at the separate building.

Example - 2 hots, a neutral, and a ground wire are run. The hots connect to opposite legs at the source service panel and are protected by 2 20 amp breakers (a multiwire branch circuit). The 2 circuits run 15/20 amp receptacles and lights in the separate building.

A single 60 amp branch circuit could probably feed a welder at the separate building but there would be no lights or 15/20 amp receptacles. (IIRC this would run afoul of other NEC requirements.)

If 2 branch circuits are run - hot-neutral, hot-neutral - a grounding electrode is required at the separate building.

bud--

Thanks Bud for the info...really too bad this section isn't worded a bit clearer to take the "coulda-woulda-shoulda" out of it...kind of keeps you guessing.

Fred

You really can't do that under normal circumstances, although I'm sure it happens.

225.30 Number of Supplies. Where more than one building or other structure is on the same property and under single management, each additional building or other structure served that is on the load side of the service disconnecting means shall be supplied by one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.

Thanks for adding the citation. I was wondering why you "couldn't".

buud--