Ground rod required in detached garage?

[richwaskowitz]

I just can't be sure whether a ground rod is required at this detached garage or not. Please cite the specific article.

1. Residential detached garage
2. No piping of any kind in the garage
3. Underground feed from house main panel via a 30 amp 2 pole breaker at 120/240 volts
4. Equipment ground and neutral is provided to 4 circuit sub-panel where neutral is isolated from ground

Do I install a ground rod and bond the neutral at the garage and not use the equipment ground in the feeder? Or do I treat this as I would a sub-panel within the house (provide an isolated neutral)?

 

[roger]

Read 250.32 of the cycle you are currently under.
NEC
Roger

 

[Dennis Alwon]

...............................

 

[Smart $]

I just can't be sure whether a ground rod is required at this detached garage or not. Please cite the specific article.

1. Residential detached garage
2. No piping of any kind in the garage
3. Underground feed from house main panel via a 30 amp 2 pole breaker at 120/240 volts
4. Equipment ground and neutral is provided to 4 circuit sub-panel where neutral is isolated from ground

Do I install a ground rod and bond the neutral at the garage and not use the equipment ground in the feeder? Or do I treat this as I would a sub-panel within the house (provide an isolated neutral)?

Grounding electrode system required (2 rods likely minimum). Neutral and Ground are isolated. GEC is connected to Ground, not Neutral.

Ref: 250.32

 

[richwaskowitz]

I tried Roger, I really did. Please help me understand. In order to fall under the exception at 250.32 (A), I must keep the supply a "branch circuit" and NOT put more breakers downstream (in a sub-panel)? Am correct in understanding that once I put a panel in the garage with even one breaker, the branch circuit feeding the garage becomes a feeder circuit and a grounding electrode system is required by 250.32?

 

[augie47]

I tried Roger, I really did. Please help me understand. In order to fall under the exception at 250.32 (A), I must keep the supply a "branch circuit" and NOT put more breakers downstream (in a sub-panel)? Am correct in understanding that once I put a panel in the garage with even one breaker, the branch circuit feeding the garage becomes a feeder circuit and a grounding electrode system is required by 250.32?

It appears Roger is off-line so I will attempt to answer for him.
"Yes" (you understanding is correct)
and your system must meet the requirements of 250 Part III

 

[tom baker]

I want to discuss the why, we have covered the how.
Grounding of electrical systems is for protection from lightning
For a branch circuit to a dwelling unit garage, no grounding electrodes are required. With a branch circuit there won't be limited electrical equipment to be damaged by lighting (only one branch circuit to a separate building)

But with a feeder, there is significant more risk from lightning. Lightning will strike a building regardless if there is any electrical equipment installed or not. Lightning does not care if its a 40 amp feeder or a 400 amp feeder.

With a feeder, a grounding electrode system is required, even a 15 amp feeder.
Bonding is done via the green wire back to the source. Whats changed since 2002 NEC is elimination of parallel current paths from the neutral and regrounding the neutral

And to further understand this issue, you should review Art 225. Every building requires a disconnecting means (read panel), with an exception for dwelling unit out buildings.