grounding portable generators

RobBlakeslee · Mar 15, 2015

I just purchased a 3600 watt portable generator to power miscellaneous construction tools at job sites without electrical power. The generator manufacturer requires the unit be properly grounded ( 5/8" grounding rod, driven 8' into the earth and attached to the unit's frame with #8 solid bonding wire). I have been told this is not necessary for the type of equipment I will be powering (circular saws, table saws, miter saws, compressors, etc.) I know of several contractors who routinely use portable generators without grounding them. I would like to get some qualified professional advice about this.

George Stolz · Mar 15, 2015

See 250.34.

Smart $ · Mar 15, 2015

Got a link to manufacturer's instructions?

While George pointed to the proper Code section (which doesn't require the rod), you may have to contend with 110.3(B) [requirement to follow instructions of listed or labeled products], especially if an accident occurs and OSHA visits the site.

George Stolz · Mar 17, 2015

Is there a generator listing that violates 250.34? I'd be interested to see it.

Smart $ · Mar 17, 2015

George Stolz said:
Is there a generator listing that violates 250.34? I'd be interested to see it.

Don't know of any. That's why I asked for a link to the instructions.

kwired · Mar 17, 2015

Tethering the unit to a ground rod kind of takes away some of the meaning of "portable" as well.:happyyes:

don_resqcapt19 · Mar 17, 2015

George Stolz said:
Is there a generator listing that violates 250.34? I'd be interested to see it.

How would adding a grounding electrode be a violation of 250.34. That section says the NEC does not require a grounding electrode. It does not prohibit the manufacturer from requiring one in the installation instructions and does not prohibit the installer from installing one if he wants to.

tom baker · Mar 17, 2015

Are portable generators listed?

Smart $ · Mar 17, 2015

tom baker said:
Are portable generators listed?

I believe some are.... with emphasis on SOME. A discussion a while back brought up a grounding requirement for UL listed portable generators under a certain rated kW.

don_resqcapt19 · Mar 17, 2015

If the generator is listed as an "Engine Generator for Portable Use (FTCN) the UL Guide Information (white book) says they must be connected as an SDS.

dereckbc · Mar 17, 2015

My 2-cents worth is it is a 3600 watt generator tells me it is something like a portable Honda genny with GFCI receptacles. Adding a GR is a complete waste of material that does nothing, and is legal mumbo jombo CYA put in there by an ambulance chaser retained by the manufacture. The genny is not made to hard wire to premises wiring or has a gen snorkel.

sandsnow · Mar 18, 2015

don_resqcapt19 said:
If the generator is listed as an "Engine Generator for Portable Use (FTCN) the UL Guide Information (white book) says they must be connected as an SDS.

The OP said the genset is only supplying portable tools. The guide info you refer to is saying SDS only when supplying a building or structure.

don_resqcapt19 · Mar 18, 2015

sandsnow said:
The OP said the genset is only supplying portable tools. The guide info you refer to is saying SDS only when supplying a building or structure.

Correct, my real point was that some are listed.

If you have a listed generator and the provided instructions call for a ground rod, that ground rod is required by 110.3(B).

George Stolz · Mar 21, 2015

George Stolz said:
Is there a generator listing that violates 250.34? I'd be interested to see it.

don_resqcapt19 said:
How would adding a grounding electrode be a violation of 250.34. That section says the NEC does not require a grounding electrode. It does not prohibit the manufacturer from requiring one in the installation instructions and does not prohibit the installer from installing one if he wants to.

don_resqcapt19 said:
Correct, my real point was that some are listed.

If you have a listed generator and the provided instructions call for a ground rod, that ground rod is required by 110.3(B).

Don, "violate" was a poorly chosen word. I was thinking more along the lines of, "Does anyone have evidence of a generator that does not correspond with the provisions of 250.34 and do require a ground rod for portable loads?"

Given the code language and the utterly counterintuitive nature of driving a ground rod for a portable generator supplying portable loads, it seems unlikely any manufacturer would require such a thing.

don_resqcapt19 · Mar 22, 2015

Here is part of the manual for one portable generator:

Generator must be grounded to prevent electrical shock from faulty appliances.
...
The system ground is not connected to the AC neutral wire. If using a receptacle tester, it will not show the same ground circuit condition as for a home receptacle. (system ground is a terminal labeled "ground terminal" on the front of the generator)

How do you ground something with out a grounding electrode given the definition of "grounded" in Article 100 (2008 and newer codes)?

sandsnow · Mar 22, 2015

don_resqcapt19 said:
Here is part of the manual for one portable generator:

How do you ground something with out a grounding electrode given the definition of "grounded" in Article 100 (2008 and newer codes)?

So that portable generator is either not listed or UL has been remiss in their "duties".

Driving a ground rod and connecting to system ground terminal will do nothing. Assuming the neutral an system ground terminal is isolated as described in the instructions.

don_resqcapt19 · Mar 22, 2015

sandsnow said:
So that portable generator is either not listed or UL has been remiss in their "duties".

There is no requirement that portable generators be listed and I don't think too many of them are.

Driving a ground rod and connecting to system ground terminal will do nothing. Assuming the neutral an system ground terminal is isolated as described in the instructions.

Exactly, but they tell you to ground it without any details as to what that means.

sandsnow · Mar 22, 2015

don_resqcapt19 said:
There is no requirement that portable generators be listed and I don't think too many of them are.

Exactly, but they tell you to ground it without any details as to what that means.

If anything it would an OSHA requirement.

Generac has good instructions. Can't copy the text, but you can look up manual here. They get it.
http://www.generac.com/service-supp...c15d-45b1-b5e8-d12e63e9faa9&isBaseModel=false

kwired · Mar 23, 2015

don_resqcapt19 said:
There is no requirement that portable generators be listed and I don't think too many of them are.

Exactly, but they tell you to ground it without any details as to what that means.

Makes more sense if you just read the bold face text, if the generators were listed, instructions included in the listing will make more sense:happyyes:

Or at least we would like to think so - but common sense seems to get a different meaning every year as time goes by.

don_resqcapt19 · Mar 23, 2015

sandsnow said:
If anything it would an OSHA requirement.

Generac has good instructions. Can't copy the text, but you can look up manual here. They get it.
http://www.generac.com/service-supp...c15d-45b1-b5e8-d12e63e9faa9&isBaseModel=false

Yes, generators, and any other equipment used in the work place, are required to be listed by OSHA.

As far as Generac, Mike Holt has worked with them on the grounding information in their manuals.

grounding portable generators

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