Grounding detached garage

[inspector 102]

Under 230.32 (B), it states that the grounding electrode shall be run with the supply conductors to a detached building. This indicates that a four-wire system is required for all panels installed in a detached garage. If there is only a three wire system (H-N-H), then can you re-establish a grounding electrode at the detached building and if yes, would you bond the grounded conductor and grounding conductor at the detached panel? Would this create a parallel path by bonding the two? If the three-wire is provided, and isolated neutral and ground, would this meet the requirements of 230.32? All confused for now.

 

[Johnmcca]

Is there any metallic path connecting the two structures? That makes the difference in what the answer is

 

[charlie b]

Under 230.32 (B), it states that the grounding electrode shall be run . . . .

I think you meant 250.32(B), and I think you meant "equipment grounding conductor." It also matters which code cycle applies, as this rule was revised in the 2008 edition.

 

[roger]

What code cycle are you under?

If you are under the 2008 a four wire feeder would be required for this detached garage, the EGC would be bonded to the panel enclosure and to an available grounding electrode.

If you are under an earlier code cycle you can treat this as you would treat a service and bond the neutral and enclosure to an available GE as long as there are no other bonded metallic paths back to the primary building.

This is assuming you are talking about a feeder verses a branch circuit

Roger

 

[inspector 102]

I am currently using the 2008 NEC, no metallic between buildings, direct burial or PVC conduit. It appears what used to be an allowable provision in 250.32 (B)(2) in the 1999 is now an exception in 2008. Under the 2008, would you consider "existing premise wiring" to mean the original wire to the first building, or would you consider it if they need to bury feeders to the new building, they shall be 4-wire assemblies? To me, "exisitng premise wiring" means if they change an existing panel only, not installing new feeder to a new building.

 

[jxofaltrds]

I am currently using the 2008 NEC, no metallic between buildings, direct burial or PVC conduit. It appears what used to be an allowable provision in 250.32 (B)(2) in the 1999 is now an exception in 2008. Under the 2008, would you consider "existing premise wiring" to mean the original wire to the first building, or would you consider it if they need to bury feeders to the new building, they shall be 4-wire assemblies? To me, "exisitng premise wiring" means if they change an existing panel only, not installing new feeder to a new building.

If I understand you, just changing the panel would be OK.

 

[Buck Parrish]

And a new feeder would require a four wire. With the equipment ground bonded to the grounding elctrode.

 

[mcclary's electrical]

And a new feeder would require a four wire. With the equipment ground bonded to the grounding elctrode.

4 wire should be seperated and isolated.

 

[roger]

4 wire should be seperated and isolated.

The neutral would be but the EGC would have to be bonded to a grounding electrode.

Roger

 

[mcclary's electrical]

The neutral would be but the EGC would have to be bonded to a grounding electrode.

Roger

Yes but isolated from the grounded conductor . I thought buck meant "bond grounded conductor to can", like a service, but I read it wrong.

 

[LarryFine]

If the feeder was compliant when it was installed, it may be used as is now.

Of course, that also means that no parallel metallic pathways may be added.