Satelite Structures Grounding Question

[Fred]

Hi Group!

Always wondered when you are sub feeding a seperate building such as a
garage from a residence service ... is it necessary to drive seperate ground
rods for the buidling/structure being sub fed or rely on the ground
conductor in the cable sub feeding the seperate building?

Would distance between the buildings matter?

Fred

 

[[email protected]]

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

 

[Fred]

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?

Fred

 

[[email protected]]

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

 

[John Gilmer]

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]

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

Fred

 

[Bud--]

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--

 

[Bud--]

OK.

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

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.

2. 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--

 

[Bud--]

From gfretwell's code section

Actually from electrician's code section.

bud--

 

[Bud--]

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

Fred

[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--

 

[Fred]

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

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

Fred

[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--

 

[[email protected]]

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

bud--

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

 

[[email protected]]

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.

 

[Bud--]

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--