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#207753 11/24/12 12:59 PM
Joined: Feb 2002
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Since the storm came and went, I would like to ask a question. With the whole house generators, what do people see out there? Are the generators manufactures instructions calling for installing a ground rod at the new generator? Or no ground rod? Or are they leaving it up to the local AHJ?
Any thoughts/comments?

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Is it installed as an SDS? That may affect the answer.


Greg Fretwell
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Typically, the instructions state ground the system per the NEC and local ordinances. It stands to reason since ground conditions vary from area to area. The local JHA determines how they are grounded

I saw a commercial from a loco poco and the flashed a resi transfer switch where all the neutrals were on the same bus. I contacted them and asking them about it and that's how they wanted wired


"Live Awesome!" - Kevin Carosa
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Greg,

Most generators only break both hot legs in a resi type set up, so I wouldn't call it a SDS. So then a ground rod would not be needed, right?

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Sparky,

All towns in NJ do not have a "Local" ordinance, We have to follow what the state adopts. For the most part the state of NJ will follow 95-99% of the NEC verbatim.

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If the generator is not an SDS, the system grounding remains the same, using the service GES. The only way you would need a ground rod was if you called it a "structure" IMHO.

250.35 still requires an equipment bonding conductor sized to 250.102(C), which tosses you back to 250.66 based on the size of the ungrounded conductors to the generator.


This does bring up an interesting conundrum. The smallest EGC in 250.66 is 8ga (but no larger than the size of the ungrounded conductors in associated rules).

#10 cable, no problem, the EGC is #10. #8 cable is a problem tho since the EGC will usually be #10.


Greg Fretwell
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Greg,

If you were using a generator to supply tents at a fair or something like that, Then I can see the need for a ground rod. You would then be generating your own neutral terminal at the gen. itself. At this point, I would think that the EGC would have to be a #6 cu to 2-grounding electrodes 6' apart.

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Quote

If you were using a generator to supply tents at a fair or something like that, Then I can see the need for a ground rod.



The funny thing about that idea is if you just have a portable generator running cord and plug loads, the NEC doesn't require a rod and grounding the neutral actually makes the installation more dangerous.


Greg Fretwell
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All the gens used at a golf tournament had 2 grd rods each bonded to the neutral buss at the main. These were 70KW to 2 MW units feeding everything from a 10x10 shade cover to 50kSF membrane structures.

We utilized some portable units, mostly for 120 volt power used while we were working. No ground rods for them.

I used a 6500W portable at my home for 18 days, grd from twistlock to my main panel. Backfed CB, LOTO on main CB.



John
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If the generator is not connected as a SDS, then a ground rod is not required by the NEC. I read that some county's in Florida require ground rods as a local ordinance because of all the lightning.

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