I will be installing a standby generator located about 50 ft. from the
grounding rod for my house. If I ground the generator only in main panel,
then there is a possibility that the generator frame will be at a slightly
different potential than the adjacent earth on which someone touching the
generator may be standing. If I install a ground rod at the generator
location, then I will be introducing a ground loop with its associated
How, according to the NEC, should the generator be grounded? Please
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. 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.
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.
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?
The gen only needs small wire attached to even a long nail driven into
the ground, a lightning rod is overkill
LOL. You guys are making me laugh tonight. Thanks. This reminds of the
person a few years back who posted about sticking a wire from her computer
out the window to a coat hanger in the ground because her house was not a
Maybe on the next job I'll connect a ground wire good for 7000 amps to a
long nail and show the inspector this thread. LOL
I really do appreciate all you folks who took the time to reply. However,
the subject began "code question" amd so far none of the replies have tried
to answer the question based on code. Also the question asked was "How,
according to the NEC, should the generator be grounded?" Does anyone have
an answer based upon their knowledge of the NEC?
As to the long nail suggestion you may be very certain that the nail will
not be connected well to the ground when it is new and much less so after
it begins to rust. That is why long ground rods are used and why two are
sometimes required. That is also why they are made of copper. Yes the
outside of the copper will corrode but the copper oxide, unlike rust, is
On Sun, 07 Sep 2008 20:52:48 -0400, email@example.com wrote:
OK short code answer.
You connect the frame of the generator to the grounding system of the
If the transfer switch also switched the white (neutral) you bond the
neutral in the generator to the frame.
(that is a separately derived system)
If the transfer switch only switches the hots do not bond the neutral,
it gets bonded via the bonding jumper in your service disconnect for
the utility feed.
That is not a separately derived system..
On Sep 7, 11:35 am, firstname.lastname@example.org wrote:
Grounding and bonding depend on whether or not is a seperatley derived
system or not. I assume you are permanantly mounting the generator
and it is not a portable unit. I also assume you are installing a
transfer switch. Is this correct? NEC 2005 Article 250 is where to
On Sun, 7 Sep 2008 18:34:22 -0700 (PDT), email@example.com wrote:
It is a permanent installation. I will not be using a transfer switch. I
will be backfeeding the panel through one of the breakers. That breaker
has a mechanical interlock which prevents both it and the main breaker
being on at the same time. (It is impossible to turn on the backfeed
breaker on unless the main is off, and impossible to turn the main breaker
on unless the backfeed breaker is off.)
Thanks for the code reference.
On Sun, 07 Sep 2008 22:05:03 -0400, firstname.lastname@example.org wrote:
OK that is what we needed to know. That is not a separaate;y derived
system, you want to remove the jumper between the ground and the
neutral in the generator. You still run a green wire ground between
the generator and your house grounding system. A rod is not needed
They differ by panel model within manufacturer and are all hideously
expensive. Here's what I did on a Square D panel.
The connection to the generator goes to a double circuit breaker located in
the upper right column. For normal, non-emergency, operation, this breaker
It's possible to fashion a metal or plexiglass plate that nudges against
both the main circuit switch and this odd circuit breaker. This plate is
bolted to the panel cover via elongated holes in the plate that allow the
plate to slide, making contact with the two switch handles. The trick is to
match the sliding with the positions of the main switch and the odd breaker.
The breaker can't be turned ON unless the main switch is OFF. The main
switch can't be turned ON unless the breaker is OFF.
On a Square D, main switch ON is to the right and circuit breaker OFF is to
the right. If you have a block plate between the levers, it's obvious the
circuit breaker can't be moved to the left (ON) unless the main is first
moved to the left (OFF) and the blocking plate moved likewise. Similarily,
the main can't be moved right (ON) unless the circuit breaker is first moved
right (OFF) and the blocking plate scooted over with it.
Get the model and make of your panel and do a search on "
interlock" The results will give you an idea of how the manufacturer of your
panel wants the thing to work. You can then either find the best price on
the "approved" device or, as I did, fashion your own.
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