Generator Grounding

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superdave02

superdave02

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Installing an MQ Power 125 portable generator on a steel base. The manufacturer's installation instructions says to install an 8' copper ground rod and a #10 copper wire to the grounding lug on the generator. The gen is actually a 100kw, so about 240 amps at 120/240 3 phase. Thoughts?
 
Is this a "stand alone" system or a stand-by with a transfer switch ?
 
this is simply a temp install until power is restored, no transfer switch. gen sits on the ground and feeds a building through the main disconnect
 
petersonra said:
IMO it does not require a grounding electrode at all. so whatever you do is fine. 250.34
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I would say the generator is part of a separately derived system and needs a grounding electrode per 250.30. I don't see anything in 250.34 that would remove that requirement in this installation.
 
If the manufacturer says to install one them I'm sure I should. I'm just going to following the NEC on that. In my own personal opinion I feel it's unnecessary.
 
Let's make it more complicated :ROFLMAO:

Where is the generator sitting? Inside the building (garage/shed/etc) or out on the parking lot? If it's inside, it wouldn't need an electrode at all, if it's outside then it starts to be a structure and probably needs a proper GES.

Make sure the SBJ is in only one place. There'll be five wires running to it anyway, but one could be a EGC or a GEC depending on where that jumper is (not that it actually matters what you call it).

FWIW, opinion is that the main purpose of grounding electrodes at a generator is to make AHJ's happy.
 
superdave02 said:
Bonded neutral, sitting outside on grass, no local inspections, federal QA QC
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Code requires an electrode and GEC for a separately derived system. The electrode should be the metal water pipe grounding electrode or structural metal grounding electrode if they are available. (250.30(A)(4)).
 
david luchini said:
I would say the generator is part of a separately derived system and needs a grounding electrode per 250.30. I don't see anything in 250.34 that would remove that requirement in this installation.
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Looks to me to be a portable generator using a cord to connect the load.

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator
shall not be required to be connected to a grounding electrode
as defined in 250.52 for a system supplied by the generator
under the following conditions:
(1) The generator supplies only equipment mounted on the
generator, cord-and-plug-connected equipment through
receptacles mounted on the generator, or both, and
(2) The normally non–current-carrying metal parts of equipment
and the equipment grounding conductor terminals
of the receptacles are connected to the generator frame.
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petersonra said:
Looks to me to be a portable generator using a cord to connect the load.
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The OP mentioned connecting the generator to the building through the main disconnect, not connecting cord-and-plug equipment through receptacles mounted on the generator.

250.34(A) wouldnt apply.
 
It would seem to me that from what the OP is describing he is connecting a genset to an existing solidly grounded system in witch case he needs to remove the bonding jumper on the genset and run an EGC to the genset. No GES would be required.
Connecting the genset with the neutral bonded as is would be a violation as the building neutral is already bonded and as such this is not a separately derived system.
 
texie said:
It would seem to me that from what the OP is describing he is connecting a genset to an existing solidly grounded system in witch case he needs to remove the bonding jumper on the genset and run an EGC to the genset. No GES would be required.
Connecting the genset with the neutral bonded as is would be a violation as the building neutral is already bonded and as such this is not a separately derived system.
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I think this is backwards...he has a separately derived system as there is no service to the building.

The system needs to be grounded per 250.30. The neutral-ground bond at the main disconnect would be need to be disconnected, unless there is something in 250.30 that allows it, and the system main bonding jumper should be at the source.
 
david luchini said:
I think this is backwards...he has a separately derived system as there is no service to the building.

The system needs to be grounded per 250.30. The neutral-ground bond at the main disconnect would be need to be disconnected, unless there is something in 250.30 that allows it, and the system main bonding jumper should be at the source.
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I was just assuming that this was an existing building with a grounded service that the OP was supplying temporarily. But, yes, of course if there is no service I would agree with you.
 
superdave02 said:
this is simply a temp install until power is restored, no transfer switch. gen sits on the ground and feeds a building through the main disconnect
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If it has no connection to the building electrical system then it sounds like it a SDS. If it's supplying existing circuits within the building well then there's other issues.
 
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