Grounding a generator

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doslover

doslover

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Oregon
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Retired Journeyman Electrician,
I have just installed a 10kv generator for a customer. Grounded the generator with a new separate # 4 copper to the existing utility ground rods. Inspector says No!
Could not find where he is right or wrong. Do not want him on my bad side. Comments ?
 
Does the transfer switch actually switch the neutral or not ?
(This will effect the grounding means.)

In general, you are probably in violation of 300.3(B)
 
Grounding a generator

augie47 said:
Does the transfer switch actually switch the neutral or not ?
(This will effect the grounding means.)

In general, you are probably in violation of 300.3(B)
Click to expand...


Neutral does not switch.
 
If the neutral is not switched then, IMHO, the generator needs a Equipment grounding conductor and, as mentioned, 300.3(B) would require that to be run with your circuit conductors.
 
augie47 said:
If the neutral is not switched then, IMHO, the generator needs a Equipment grounding conductor and, as mentioned, 300.3(B) would require that to be run with your circuit conductors.
Click to expand...

Have a #8 ground wire from transfer switch to ground lug in generator control panel. The
# 4 copper is from the external ground lug to rods.
 
In that case, I don't see a problem.....
did the inspector give you a Code reference ?

(shot in the dark.. if the generator neutral bonded to the frame ?)
 
Last edited:
doslover said:
Thanks for the feedback. Sort of the direction I was thinking.
I'll see if i can get the inspector to reconsider.

Regards.
Click to expand...

After rereading the post I think you have violated 300.3 B. Since you have an EGC ran with the phase conductors you are good. But you have ran another EGC outside the phase conductors to the utility rods. Had you just driven another rod at the gen and bonded it with your EGC in the gen. then it would have been OK. Supplemental rod. You may also want to check the install instructions as most state to drive a rod at the gen.

(shot in the dark.. if the generator neutral bonded to the frame ?)
Click to expand...

That is something you need to verify. In this install there is no connection between the neutral and ground.
 
Pierre C Belarge said:
250.32 does not apply to generators (optional Standby - which is like 90% of all generator installations).....

The reason for grounding generators is based on installation instructions from the manufacturer.
Click to expand...
And, some generator mfgs take the easy way and require ground rods, because AHJs and electricians don't understand the rules. By some I mean Siemens and Generac. I went to a seminar and they said we require ground rods regardless of the what the NEC requires. Cummins has a good set of drawings that clearly shows a single point ground.
What our AHJs state is if the mfg requires ground rods, then we require ground rods.
 
But have we answered the orignal question?

Have a #8 ground wire from transfer switch to ground lug in generator control panel. The
# 4 copper is from the external ground lug to rods.
Click to expand...

Grounded the generator with a new separate # 4 copper to the existing utility ground rods. Inspector says No!
Click to expand...
 
ceb58 said:
But have we answered the orignal question?
Click to expand...

Thank you ceb58

The generator manufacturer says to ground the unit with ground rods.

There neutral and ground are not connected.

I have a # 8 wire running with the generator circuit.

I have installed a # 4 wire from the generator housing lug to the ground rods used by the utility.

Can I share the ground rods ??
 
doslover said:
Thank you ceb58

The generator manufacturer says to ground the unit with ground rods.

There neutral and ground are not connected.

I have a # 8 wire running with the generator circuit.

I have installed a # 4 wire from the generator housing lug to the ground rods used by the utility.

Can I share the ground rods ??
Click to expand...

I will say no. The mfg. instructions tell you to drive a rod then drive a rod and tie it to the lug. Get rid of the #4 from gen. to utility rods and keep the #8.

250.32 does not apply to generators (optional Standby - which is like 90% of all generator installations).....

The reason for grounding generators is based on installation instructions from the manufacturer.
Click to expand...
Pierre's comment is correct. Code wise you are not requried to drive a rod at the gen. but most mfg. instructions state a rod is requried so not driving one violates 110.3 B.
 
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