Code question on generator grounding

Posted by on September 7, 2008, 7:08 pm

>> Lightning protection? You got wire that'll handle 7,000 Amps?

Actually up to a record 200,000 amps has been measured, however it lasts
for only about a millisecond so the wire will not heat appreciably during
that short time.

Most commonly, the lightning current ceases in about a millisecond for a
given stroke, but sometimes there is a continuing current on the order of
100 amps following one or more of the strokes. This is called "hot
lightning" and it is the cause of lightning fires. The continuing current
only lasts for only 0.2 seconds and so a typical ground wire is sufficient.

Posted by HeyBub on September 7, 2008, 9:45 pm

John Grabowski wrote:

>> John Grabowski wrote:

>>> There should be grounding requirements in the installation
>>> instructions. Generally there is an external ground lug on the frame
>>> or housing of the generator. This would get connected to your
>>> grounding electrode conductor for lightning protection. There
>>> should also be an equipment grounding conductor that is run with
>>> generator conductors to the transfer switch or panel that you will
>>> be supplying the generator power to.

>> Lightning protection? You got wire that'll handle 7,000 Amps?

> LOL. What do you think ground rods are for? For a generator a #10
> may only be required. For a house a #6 or #4 will suffice.

Well, they sure as hell ain't for lightning protection!

Posted by John Grabowski on September 8, 2008, 8:01 am

> John Grabowski wrote:

>>> John Grabowski wrote:
>>>> There should be grounding requirements in the installation
>>>> instructions. Generally there is an external ground lug on the frame
>>>> or housing of the generator. This would get connected to your
>>>> grounding electrode conductor for lightning protection. There
>>>> should also be an equipment grounding conductor that is run with
>>>> generator conductors to the transfer switch or panel that you will
>>>> be supplying the generator power to.
>>> Lightning protection? You got wire that'll handle 7,000 Amps?

>> LOL. What do you think ground rods are for? For a generator a #10
>> may only be required. For a house a #6 or #4 will suffice.

> Well, they sure as hell ain't for lightning protection!

LOL. I printed this thread to show some of my fellow electricians. They
will get a good laugh like I did. Thanks for making my week.

Posted by CL \"dnoyeB\" Gilbert on September 8, 2008, 12:00 pm

John Grabowski wrote:

>> John Grabowski wrote:

>>> There should be grounding requirements in the installation
>>> instructions. Generally there is an external ground lug on the frame
>>> or housing of the generator. This would get connected to your
>>> grounding electrode conductor for lightning protection. There should
>>> also be an equipment grounding conductor that is run with generator
>>> conductors to the transfer switch or panel that you will be supplying
>>> the generator power to.

>> Lightning protection? You got wire that'll handle 7,000 Amps?

>
>
> LOL. What do you think ground rods are for? For a generator a #10 may
> only
> be required. For a house a #6 or #4 will suffice.

This was my question as I read this thread. The OP said something about
standing next to the generator and having different potential. But my
understanding about "grounding" in this case is that its about lightning.
I don't think there will be any current flow from the generator through a
person's feet and into the soil no matter how its wired or what he touches.
Is that correct?

CLG

Posted by ransley on September 7, 2008, 6:58 pm

> >I will be installing a standby generator located about 50 ft. from the
> > grounding rod for my house. =A0If I ground the generator only in main p=

anel,

> > then there is a possibility that the generator frame will be at a sligh=

tly

> > different potential than the adjacent earth on which someone touching t=

> > generator may be standing. =A0If I install a ground rod at the generato=

> > location, then I will be introducing a ground loop with its associated
> > problems.
> > How, according to the NEC, should the generator be grounded? =A0Please
> > provide a code reference (or quote) if you can.
> > Many thanks for any help.

> There should be grounding requirements in the installation instructions.
> Generally there is an external ground lug on the frame or housing of the
> generator. =A0This would get connected to your grounding electrode conduc=

tor

> for lightning protection. =A0There should also be an equipment grounding
> conductor that is run with generator conductors to the transfer switch or
> panel that you will be supplying the generator power to.

The gen only needs small wire attached to even a long nail driven into
the ground, a lightning rod is overkill

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Code question on generator grounding - Page 2