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#163090 - 04/30/07 06:04 PM Guard shack ground rod?  
drillman  Offline
Member
Joined: Mar 2003
Posts: 97
Somewhere in Texas
Due to construction we are putting in a temp guard shack. It is about 4x8 with a window AC, a light and a few plugs for battery chargers. It is made of steel, with windows on 3 sides. It is going to be powered by a small portable generator. There will be one 20 amp circuit for the whole shack.

Question one is do we need to drive a ground rod for this shack powering it from a portable generator?

Question two is the same, except what if we powered it with a single circuit from the nearest building?

As for the term "temp", construction is scheduled to take place for 18 months. The shack will be removed after the construction and put someplace else.

Many thanks for any help.


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#163093 - 04/30/07 07:14 PM Re: Guard shack ground rod? [Re: drillman]  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
I would bring 2 circuits on a 3-wire, as it sounds a bit much with the AC unit.

Otherwise, the answers IMPO are maybe to #1, and maybe on #2. (See 250.32) FYI a 3-wire is still a single circuit if it has a handle-tie on the OCP. Either way the #2 answer depends on if there are parralel metallic paths to the shack and the building the circuit comes from.

Quote
250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be grounded and shall be permitted to serve as the grounding electrode 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 non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
Portable describes equipment that is easily carried by personnel from one location to another. Mobile describes equipment, such as vehicle-mounted generators, that is capable of being moved, on wheels or rollers.
The frame of a portable generator is not required to be connected to earth (ground rod, water pipe, etc.) if the generator has receptacles mounted on the generator panel and the receptacles have equipment grounding terminals bonded to the generator frame.

Last edited by e57; 04/30/07 07:19 PM. Reason: changed

Mark Heller
"Well - I oughta....." -Jackie Gleason

#163094 - 04/30/07 07:24 PM Re: Guard shack ground rod? [Re: drillman]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
I say "no."

Separate structures require rods only when there is more than one circuit.

The generator introduces another important item. Electricity does not try to go to "ground" so much as try to go back home ... "home" in this case being the generator. So. I'd pay particular attention to that ground wire.


#163099 - 04/30/07 07:40 PM Re: Guard shack ground rod? [Re: renosteinke]  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 791
Chicago, Il.
I think that your considerations should lean more towards what might be prudent for lightning protection than for earthing the generator. Depending on the surrounding structure distances and heights, that is probably where your greatest danger lies.
Joe


#163100 - 04/30/07 07:59 PM Re: Guard shack ground rod? [Re: renosteinke]  
e57  Offline
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Joined: May 2003
Posts: 2,876
S.F.,CA USA
Originally Posted by renosteinke
I say "no."

Reno, we don't know what the generator is... Or if this metal shack is "premisis" wired. If everything is not cord and plug connected to the generator, he'll need a rod, single circuit or not. Sure one could go for the exception for single circuit if wired from a building, but not sure if I would with a metal shack.

Last edited by e57; 04/30/07 08:10 PM.

Mark Heller
"Well - I oughta....." -Jackie Gleason

#163101 - 04/30/07 08:03 PM Re: Guard shack ground rod? [Re: drillman]  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
Originally Posted by drillman
As for the term "temp", construction is scheduled to take place for 18 months. The shack will be removed after the construction and put someplace else.


This depends on local codes... Temp here means 90 days or less.


Mark Heller
"Well - I oughta....." -Jackie Gleason

#163103 - 04/30/07 09:27 PM Re: Guard shack ground rod? [Re: e57]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Right, Marc .. there's a lot we don't know. Heck, it can't hurt to bang in a rod ... but, of the two sorts of "grounding," I put the emphasis in grounding / bonding everything back to the generator, and worry less about Mother Earth.

Code is quite clear - don't count on dirt to carry any current. I say that ground wire back to the genny is the priority.



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