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#173992 01/24/08 08:54 PM
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jem Offline OP
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Customer wants to use a portable generator to power some house circuits. This generator has bonded nuetral/ ground. Since generator is bonded, must I use a transfer switch that switches the nuetral and can the existing ground rod be used for grounding the generator.

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jem #173995 01/24/08 09:09 PM
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Yes, switch the neutral.

No, you don't tie s portable generator to the ground rod.

If he's mounting the generator permanently, it's no longer a portable generator.

My advice? If you're using a portable genny, use extension cords, and portable lights too. Don't even try to tie it in. If you want a stand-by genny, get a real one, and install it properly.

jem #173996 01/24/08 09:10 PM
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You should always use a transfer switch. And yes on the ground rod


"Live Awesome!" - Kevin Carosa
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Originally Posted by renosteinke


My advice? If you're using a portable genny, use extension cords, and portable lights too. Don't even try to tie it in. If you want a stand-by genny, get a real one, and install it properly.


Agreed. For the generator at home, the extension cords live in a box all marked with where they run to (fridge 1, fridge 2, freezer and lights).

The lights are also in the box (2x 240VAC trouble lights with rough service 250-260V globes fitted). The generator has four outlets fitted for the four main leads with a double adaptor on the end of the lighting lead.

Piece of pie when needed, no hunting around for leads when you need them.

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Originally Posted by sparkyinak
You should always use a transfer switch. And yes on the ground rod


You never tie a portable generator to a grounding system associated with a house, otherwise you may get circulating earth currents, at the least you may get noise on you radio, at the worst you could kill someone.

A generator is a seperately derived system, it should always be kept away from the mains wiring, unless it is fed in through a transfer switch.

I have to go with what Darren and John are saying, if you only need power when the mains fails and you don't need it instantly, I would go for the labelled flexes and lights, etc.
After all, you can't run a whole house on most "portable" generators anyway.

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Originally Posted by Trumpy
You never tie a portable generator to a grounding system associated with a house, otherwise you may get circulating earth currents, at the least you may get noise on you radio, at the worst you could kill someone.


Mike, under the NEC that really depends on the installation.


Bob Badger
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I think the key word here is "portable."

Some folks think that they are somehow improving things if they bang a ground rod whenever they use a portable, or vehicle mounted, generator. I think we've established that doing so accomplishes nothing ... as the ground rod is essentially irrelevant to clearing faults.

That everything in the building needs to be bonded, and that these paths need to go back to the generator, is another subject. That's why I say "switch the neutral;" there's no way for the electricity to go anywhere else.

Naturally, I assume that the extension cords have intact three-prong plugs!

I don't think I have ever run a wire from a genny, directly to a ground rod. Rather, the transfer switch provided the point where the generator ground was tied into the building's ground system. With a portable genny, this is accomplished by that third prong on the plug.

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I am not sure why they would even bond a truly portable generator. What is the point? A single frame to neutral fault is exactly what you are doing with the bond and two phases faulted to the frame would operate the OC device anyway (HOPEFULLY)
neither is actually a "grounded" conductor. It is arbitrary which one you bond.


Greg Fretwell
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jem Offline OP
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I see portable generators cord connected via a 4 wire cord to a power inlet on a generator panel fairly frequently. What I would like to know is if the portable generator is bonded (internal to the unit) and the neutral is switched at the transfer switch (seperately derived system) a grounding electrode is required. Can a tap be run from the service GEC to accomplish this. If the neutral is not switched (not a seperately derived system), you have a bond at the generator on the load side of the service disconnect when the generator is plugged in.

jem #174142 01/27/08 02:41 PM
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If the generator has the neutral bonded to "ground" in the generator and a switched neutral is employed in the transfer switch ( as it should be with a bonded generator neutral), a ground electrode should not be used or needed because the neutral is still bonded to ground through the generator.. Doing anything else may cause circulating currents in the grounding / bonding conductors and will defeat the purpose of the switched neutral in the transfer switch.

A.D

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