Standby Generator Ground Rod Code Needs To Be Clearer

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Birken Vogt

Senior Member
Location
Grass Valley, Ca
I thought this had been settled but apparently not. Sorry to beat this dead horse. Code references 2014.

So the manufacturers have completely removed the ground rod terminals from the outside of smaller automatic standby gensets. It is my opinion that they are not required where the neutral is solid and bond made over at the main service. And I would say most here agree.

But in trying to put together a comprehensive list of code citations I find it is more convoluted than I remember.

250.30 Informational note 1 says that it is not a separately derived system. Difficult to follow all the rabbit trails and convince another person this applies.

702.11 does not apply but I wish there was something like it for permanent non separately derived generators. It is just so plain to read.

Is there anything else I am missing?
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Assuming you're referring to small generators for SFD backup I'm not sure why one would want to setup these generators as an SDS. You have a home with a perfectly good GES so why not use it and forget about driving ground rods?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
The CODE could always make things a bit clearer and you are welcomed to submit a change to that end.
Keep in mind, however, the CODE is not an instruction manual and those using it are expected to be able to address the variables involved such as SDS vs Non-SDS.
The installation manuals (who reads those :D) for the Transfer Switches and/or Generators might be the best place for clarification if they have not done so,
 

Birken Vogt

Senior Member
Location
Grass Valley, Ca
Assuming you're referring to small generators for SFD backup I'm not sure why one would want to setup these generators as an SDS. You have a home with a perfectly good GES so why not use it and forget about driving ground rods?

What I am saying is that as a non-SDS of course it does not need a ground rod. I don't want to install a ground rod and I thought everybody knew it was not necessary but apparently not.

But trying to convince an inspector of that I have to go through pages and pages of definitions and finally culminating in [250.30 informational note 1].

I wonder why 702.11 only applies to portables?
 

kwired

Electron manager
Location
NE Nebraska
Sounds like you are understanding code correctly, but need ideas of how to beat some sense into the inspector.

Behavioral correction techniques or even torture methods can't be talked about in the grounding/bonding forum, you have to go to campfire chat:D
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
While the wording isn't great it is there to support your argument. Sometimes a graphic will help.

Fig%202.jpg
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Assuming you're referring to small generators for SFD backup I'm not sure why one would want to setup these generators as an SDS. You have a home with a perfectly good GES so why not use it and forget about driving ground rods?
From the UL Guide Information for "Engine Generators for Portable Use" (FTCN)
When a portable generator is used to supply a building or structure wiring system:
1. The generator is considered a separately derived system in accordance with ANSI/NFPA 70, "National Electrical Code" (NEC).​
2. The generator is intended to be connected through permanently installed certified transfer equipment that switches all conductors other than the equipment grounding conductor.​

 

Birken Vogt

Senior Member
Location
Grass Valley, Ca
The provided graphic perfectly illustrates the problem. The provided graphic references 250.20(D) FPN 1. This is how it used to read with California additions which made it even clearer:

But it has completely disappeared from the 2014 NEC/2016 CEC. Now section D references impedance grounded systems, and there is no more FPN 1. Why was this deleted I wonder?

Any of you code wizards have access to the rationale behind this? Or was it moved elsewhere in the code and I have just not found it?

Separately d Derived . Systems. Separately derived systems, as
covered in 250.20(A) or (B), shall be grounded as specified
in 250.30(A). Where an alternate source such as an on-site
generator is provided with transfer equipment that includes a
grounded conductor that is not solidly interconnected to the
service-supplied grounded conductor, the alternate source (de-
rived system) shall be grounded in accordance with
250.30(A).
FPN No. 1: An alternate ac power source such as an on-
site generator is not a separately derived system if the
grounded conductor is solidly interconnected to a
service-supplied system grounded conductor. An exam-
ple of such situations is where alternate source transfer
equipment does not include a switching action in the
grounded conductor and allows it to remain solidly con-
nected to the service-supplied grounded conductor when
the alternate source is operational and supplying the load
served.
 
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