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Old 02-27-2010, 09:19 AM   #1
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Off grid Generator/Inverter grounding


I have an off grid cabin. I have wired the cabin conventionally in the event I ever get electric in the area. When I say conventional, I mean, main service panel has the nuetral and ground bonded and they connect to a ground electrode(GE).
I have installed a generator house (as I call it) about 100 feet from the cabin. I will run cable underground and through a GFIC. I have a battery powered inverter and a generator hooked up to an automatic transfer switch inside the genny house. Both the genny and the inverter state the nuetral and ground are bonded inside each item. This presents a problem from every thing I have read.
How do I solve this ground and neutral issue?
Also, I am told by the genny and inverter manuals to ground each chassis to a GE. Do I need to ground the genny house with a separate GE?
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Old 02-27-2010, 11:59 AM   #2
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So far as a GFCI on the generator, the following manufacturer recommends disconnecting the internal neutral to ground bonding on the generator, then placing a label on the generator that it is not OSHA compliant...
http://www.gen-tran.com/assets/pdfs/...Bulletin20.pdf

Another solution is to use a "neutral switching" transfer switch.

As to code, this is the *most* confusing subject there is, but if you want to read about all this, search for the following...

Separately derived system...
http://www.google.com/#hl=en&safe=of...a94940edcea411

Non-separately derived system...
http://www.google.com/#hl=en&safe=of...a94940edcea411
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Old 02-27-2010, 08:16 PM   #3
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The conundrum exists because the transfer switch upstream of the main panel is now the main disconnect, turning the main panel into a subpanel.

Using a neutral transferring switch you have to unbond the neutrals and ground at your main panel, given that the transfer swtich is upstream of the main panel.

But what if you did this instead? Don't bond the generator frame to the grounding electrode but instead leave the generator neutral bonded to the generator frame and connect the ground electrode to the GFCI load side Neutral, namely to the far side of the GFCI (relative to the generator). This way the main panel remains the point where ground and neutral are bonded.

This last case mimics the normal service drop; ground and neutral are one and the same from the panel through the transfer switch to the generator. The GFCI in the generator does not do anything any more. (With ground and neutral combined, the hot current and the neutral current will always be equal). What we are accomplishing here is preventing nuisance trips while not having to modify either the generator or the panel.
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Last edited by AllanJ; 02-27-2010 at 08:19 PM.
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Old 02-28-2010, 08:05 AM   #4
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True it will work....but NEC requires a GFIC for underground cable installation...and essentially using this meathod you just took GFIC out. Won't using this method fail inspection?

NEC requires the N/G are bonded at service entrance. I think my service entrance will be the Genny/inverter..right? So I should drop a GE at my genny house and disconnect the N/G bond at the main...because now the cabin main panel is essentially a sub panel for all intents and purposes...I think.... this is confusing.
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Old 02-28-2010, 08:40 AM   #5
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My interpretation (not a pro) would be to do what you just said.

Ground rod at cabin connected to GEC. Diconnect bond.
Ground rod at genny house, bonded.
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Old 02-28-2010, 12:21 PM   #6
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A gfci is not required for underground cable.
The depth of the install is determined by the use of a gfci or not.
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Old 03-01-2010, 06:20 PM   #7
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Quote:
Originally Posted by jbfan View Post
A gfci is not required for underground cable.
The depth of the install is determined by the use of a gfci or not.
Can you give me that section in the code Please?

Short answer, at what depth do you not need a GFCI? 24" and below?
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Old 03-01-2010, 06:27 PM   #8
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I have a 60a sub panel feed running underground to my pool cabana
GFCI not required
Undergound 15a & 20a runs going out to the yard
The run does not have to be protected on these, an outside outlet does

You can bury a 15a/20a run @12" depth IF it is GFCI protected before it goes undeground
If not protected 1st then 16" depth needed
Burial depths depend upon the wire used (direct burial or conduit), if it goes under a walkway, driveway etc
And if you pour concrete on top of the run to protect the run



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Old 03-02-2010, 05:06 AM   #9
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Quote:
Originally Posted by Scuba_Dave View Post
You can bury a 15a/20a run @12" depth IF it is GFCI protected before it goes undeground
If not protected 1st then 16" depth needed
Burial depths depend upon the wire used (direct burial or conduit), if it goes under a walkway, driveway etc
And if you pour concrete on top of the run to protect the run

Ok, what about a 50amp line 74' underground X 24" deep in PVC conduit?
GFCI?
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Old 03-02-2010, 07:43 AM   #10
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There isn't any requirement to protect an undeground feed
This can of course depend upon the application
An underground feed direct to hot tub is a 50a GFCI
Because it does not feed any other circuit, just the hot tub

A 50a underground run to a sub panel usually is not
One reason being if something trips the GFCI & there are 6-12 circuits with multiple outlets it can be a PIA to find out what caused the trip
What you are doing would be like protecting an underground feed to a house



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Old 03-02-2010, 09:20 AM   #11
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A more fundamental question, may I install a whole house generator without rewiring the main panel to be a subpanel (separating neutrals and ground)?

This would depend on whether treating the transfer switch as the main disconnect is a gray area as opposed to a cut-and-dry looks like a duck quacks like a duck.

Another question, what is the GFCI in a generator supposed to protect? For a stand alone generator "in the field" the GFCI of course protects the things plugged into the generator. For a hard wired generator, the things in the house that needed GFCI protection already have GFCI's and the things not GFCI protected didn't need that protection. If the generator is hard wired in such a way that its built in GFCI never trips, then there is no great loss. For the hot tub, there is (should be) a GFCI specifically for it regardless of whether the GFCI is on the near side or the far side of an underground cable.
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Last edited by AllanJ; 03-02-2010 at 09:24 AM.
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