Grounding a generator for a cabin

[wonsweet67]

I am stationed overseas right now, no code book handy!! My friend and I were talking about his cabin we are going to wire when we get back, about getting power from a portable 5500W generator. He is going to bolt the gen down and permanantly wire it to the cabin. I was discussing the grounding with him, stating that the gen be considered the "main service" , and the cabin be an outbuilding. without having a book to refer to some of the questions I have, I was just trying to come up with the right solutions for the wiring from the gen to the cabin (not carrying the ground and pounding rods vs. not) and the grounding on the gen and the cabin? Thanks for time !!

 

[iceworm]

I am stationed overseas right now, no code book handy!! My friend and I were talking about his cabin we are going to wire when we get back, about getting power from a portable 5500W generator. He is going to bolt the gen down and permanantly wire it to the cabin. I was discussing the grounding with him, stating that the gen be considered the "main service" , and the cabin be an outbuilding. without having a book to refer to some of the questions I have, I was just trying to come up with the right solutions for the wiring from the gen to the cabin (not carrying the ground and pounding rods vs. not) and the grounding on the gen and the cabin? Thanks for time !!

I can tell you what I did. Quien Sabe? It may even be right.

I've got a 3.3kw gen, batteries and a 3kw inverter/30A charger. The gen is quiet and has a BIG muffler. I pulled the wheels, set on blocks to provide access for oil drain. And I put it in its own house about 70' away. I can still hear it, but it is pretty, uhhh, muffled :roll:

First off, forget you have a service - because you don't. The portable 5.5kw gen will have a 30A CB and a 30A, 240V, 4w receptacle (high probability). The feed from the gen to the gen house panel is a feeder, not a service. The feed from the gen to the cabin is a feeder not a service.

In my case:
Removed the NG bond from the gen,

Ran 4W, 240 from the gen 30A receptacle to a small (2 ckt) MLO panel in the gen house. Lights, vent fan, one receptacle. No bond in the gen house panel. Ground rod at the gen house GEC connected to genhouse panel ground bar.

Ran 4w from the genhouse panel to the cabin panel (actually to the inverter - then 4w from the inverter output to the panel. The inverter just passes through - relay- when the gen is on)

NG bond is in the cabin panel. Ground rod at the cabin panel.

I'm clear north, so there were a few other issues - but not related to your OP.

You have a computer. You can get access to an NEC code

ice

 

[delectric123]

so when would be an instance when the N-G bond should be at the generator?

 

[jumper]

so when would be an instance when the N-G bond should be at the generator?

When you wire it as a SDS and switch the neutral.

I can post graphics if it would help explain.

Found quick thread with graphics.

http://forums.mikeholt.com/showthread.php?t=138460

 

[ceb58]

If the generator is the only source of power it would be installed as a SDS. Look at 250.35 (A)

250.35 Permanently Installed Generators. A conductor
that provides an effective ground-fault current path shall be
installed with the supply conductors from a permanently
installed generator(s) to the first disconnecting mean(s) in
accordance with (A) or (B).
(A) Separately Derived System. If the generator is installed
as a separately derived system, the requirements in
250.30 shall apply

. So by this and 250.30 their would be a ground rod at the generator with the N-G bonded.

 

[delectric123]

When you wire it as a SDS and switch the neutral.I can post graphics if it would help explain.Found quick thread with graphics.http://forums.mikeholt.com/showthread.php?t=138460

could you please post the graphics? i can not access the links due to restricted Internet access.

 

[iceworm]

If the generator is the only source of power it would be installed as a SDS. Look at 250.35 (A) . So by this and 250.30 their would be a ground rod at the generator with the N-G bonded.
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ceb -
Thanks for bringing this up. 250.35 is new (2008) and pretty interesting. I had not paid any attention to it - but should have. Most of my clients are self-generated. A few have only one generator.

I went over 250.35, 2011 and 2008. This is a first reading only, but I don't have a good feeling about where this is headed. The section appears to be written to cover residential grade generation. Most of the permanently installed stuff I deal with does not have any CB on the gen skid. The first CB could be 500' away.

There are a whole bunch of issues with industrial, SDS, non-sds, single gen, multiple gen. And 250.35 does not limit the scope to prpbably what it should - residential. But this is a subject for another thread.

ice

 

[iceworm]

If the generator is the only source of power it would be installed as a SDS. Look at 250.35 (A) . So by this and 250.30 their would be a ground rod at the generator with the N-G bonded.
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Ground rod at the gen yes. NG bond - not necessarily. Look at 250.35.B. Likely there will be a CB on the gen skid.

Curiosity Q: What makes the difference between "portable" and "permanently mounted"? I'm looking at residential grade applications.

Portable gen, took off the wheels, bolted to the floor, cord and plug connected to a structure panel. Portable? Permanent?

Portable gen, took off the wheels, set on blocks, cord and plug connected to a structure panel. Portable? Permanent?

Portable gen, took off the wheels, bolted to the floor or on blocks, hard wired to structure panel panel. Portable? Permanent?

Portable gen, leave the wheels on, chock the wheels so it can't run around, hard wired to structure panel panel with flex. Portable? Permanent?

I'm thinking any of these are permanent (maybe - or not) :?

ice

 

[GoldDigger]

Ground rod at the gen yes. NG bond - not necessarily. Look at 250.35.B. Likely there will be a CB on the gen skid.

If the generator has a difficult to remove NG bond, then it should be the only place where the two are bonded together. If there is no hard-to-remove NG bond at the generator, it may be preferable to put the bond at the main disconnect for the building. But it should only be in one place. And it needs to be re-examined if the generator is replaced down the line to make sure that there is one and only one bond.
If there is no GFCI breaker at the generator, it may not make any practical difference if there is more than one bond.

 

[ceb58]

Ground rod at the gen yes. NG bond - not necessarily. Look at 250.35.B. Likely there will be a CB on the gen skid.








ice

From the OP I would guess that the generator is the only source and there is no POCO service. But to get deeper into the subject

GENERAL
This category covers internal-combustion-engine-driven generators rated
15 kW or less, 250 V or less, which are provided only with receptacle outlets
for the ac output circuits. The generators may incorporate alternating or
direct-current generator sections for supplying energy to battery charging
circuits.

When a portable generator is used to supply a building 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 Listed transfer equipment that switches all conductors other
than the equipment grounding conductor.

3. The frame of a Listed generator is connected to the equipment grounding
conductor and the grounded (neutral) conductor of the
generator. When properly connected to a premises or structure, the
portable generator will be connected to the premises or structure
grounding electrode for its ground reference.

4. Portable generators used other than to power building structures are
intended to be connected to ground in accordance with the NEC.

So if there is POCO power the UL listing calls for the generator to be installed as a SDS which would require the neutral to be switched. Ether way its a SDS.

 

[iceworm]

From the OP I would guess that the generator is the only source and there is no POCO service. But to get deeper into the subject So if there is POCO power the UL listing calls for the generator to be installed as a SDS which would require the neutral to be switched. Ether way its a SDS.

Don't install as a portable. As you likely guessed, I'm not a fan of switched neutrals. And unless the gen is a stand alone, portable, cord and plug connected with integral receptacles, I'm not a fan of having an internal NG bond.

ice