NEC 250.32 (A) Exception & 250.32(B)(1)

[erickench]

I look at these two NEC rules and I see a potential conflict. 250.32(A)Exception state's the following:

A grounding electrode shall not be required
where only a single branch circuit, including a multiwire
branch circuit, supplies the building or structure and the
branch circuit includes an equipment grounding conductor
for grounding the normally non?current-carrying metal
parts of equipment.

But immediately following 250.32(B)(1) state's something different:

An equipment grounding conductor as described in 250.118 shall be
run with the supply conductors and be connected to the building or structure disconnecting means and to the
grounding electrode(s).

I assume in the first case that if there's a ground wire then a grounding electrode is not needed. But in the second case I guess they mean a continuous metal raceway that is bonded would have to be connected to a grounding electrode. Otherwise the two rules conflict.

 

[Dennis Alwon]

I look at these two NEC rules and I see a potential conflict. 250.32(A)Exception state's the following:

A grounding electrode shall not be required
where only a single branch circuit, including a multiwire
branch circuit, supplies the building or structure and the
branch circuit includes an equipment grounding conductor
for grounding the normally non?current-carrying metal
parts of equipment.

But immediately following 250.32(B)(1) state's something different:

An equipment grounding conductor as described in 250.118 shall be
run with the supply conductors and be connected to the building or structure disconnecting means and to the
grounding electrode(s).

I assume in the first case that if there's a ground wire then a grounding electrode is not needed. But in the second case I guess they mean a continuous metal raceway that is bonded would have to be connected to a grounding electrode. Otherwise the two rules conflict.

Eric, we are looking at the difference between a feeder and a mwbc. In case one you could run a 12/3 with ground (doesn't have to be #12) and install a main disco at the building and install a DP breaker at the source and you are good to go.

In case 2 we are looking at a feeder to a panel regardless of the wiring method. DB, PVC etc-- they all require potential 2 rods unless you meet the 25 ohm rule or have an CCE installed or other acceptable means.

 

[roger]

Eric, we are looking at the difference between a feeder and a mwbc. In case one you could run a 12/3 with ground (doesn't have to be #12) and install a main disco at the building and install a DP breaker at the source and you are good to go.

In case 2 we are looking at a feeder to a panel regardless of the wiring method. DB, PVC etc-- they all require potential 2 rods unless you meet the 25 ohm rule or have an CCE installed or other acceptable means.

And I agree with Dennis.

Roger

 

[erickench]

Yes but the heading say's: Supplied by a Feeder or Branch Circuit. They mean both.

 

[Dennis Alwon]

Yes but the heading say's: Supplied by a Feeder or Branch Circuit. They mean both.

Yes, the article is referencing both conditions and they give the appropriate installation for each one.

 

[erickench]

You know what? I just looked at 250.32(D)(2). It say's something about a building being supplied by more than one branch circuit. Therefore the heading of 250.32(B) could mean a feeder going into a panelboard and then branch circuits are coming out of it. If a building is supplied by a branch circuit only and not a feeder then no grounding electrode is required provided there is a ground wire. But if there is feeder going into a panelboard with branch circuits coming out then you would need a grounding electrode.

 

[ceb58]

You know what? I just looked at 250.32(D)(2). It say's something about a building being supplied by more than one branch circuit. Therefore the heading of 250.32(B) could mean a feeder going into a panelboard and then branch circuits are coming out of it. If a building is supplied by a branch circuit only and not a feeder then no grounding electrode is required provided there is a ground wire. But if there is feeder going into a panelboard with branch circuits coming out then you would need a grounding electrode.

You know what? Your correct

 

[roger]

If a building is supplied by a branch circuit only and not a feeder then no grounding electrode is required provided there is a ground wire. But if there is feeder going into a panelboard with branch circuits coming out then you would need a grounding electrode.

By George, I think you've got it.

Roger

 

[erickench]

It's just the way it's written. They should clarify that the branch circuits are either supplying a building or are coming out of a panelboard.

 

[Dennis Alwon]

It's just the way it's written. They should clarify that the branch circuits are either supplying a building or are coming out of a panelboard.

I would advise reading the def. of branch circuit and feeder. I am not sure I understand your above statement. A branch cir. can feed the detached building from a panelboard and not connect to any other panelboard. If it connects to a panelboard in the detached structure then that wire is no longer a branch cir but has now become a feeder.

It seems quite clear so I was wondering if I was missing something more.

 

[erickench]

Well maybe they should'nt use the words:"Supplied by a Feeder or Branch Circuit." They should just say "Feeder" and not "Branch Circuit".

 

[Dennis Alwon]

Well maybe they should'nt use the words:"Supplied by a Feeder or Branch Circuit." They should just say "Feeder" and not "Branch Circuit".

Basically the rule for MWBC is there as an exception to the rest of the articles requirements.

 

[erickench]

I know but it still looks like a conflict.

 

[iwire]

It's just the way it's written. They should clarify that the branch circuits are either supplying a building or are coming out of a panelboard.

I have no idea what you mean. :-? The panelboard has nothing to do with it.

If you have a separate structure that is supplied by a feeder (see article 100) there must be a grounding electrode system located at the separate structure.



If you have a separate structure that is supplied by a branch circuit (see article 100) we are not required to have a grounding electrode system located at the separate structure.

A multi-wire branch circuit can be considered one circuit.