I am aware that "all generators must be grounded". In the instance of
a standby portable generator like this
how would I ground it? I have two options:
1. Ground it to a new grounding rod (expensive and involves actual
2. Ground it to the home grounding system, such as copper pipes in the
utility room, or even better next to the existing home ground
Which option here is more legal and more safe?
Ground it to the home system.
I don't know the code details, but there is bare wire, known as "bonding
wire", that code requires run without any splices from the box to the actual
The important thing is that the ground be redundantly robust.
If there is a ground fault, a hot-to-ground leak in a powered appliance
would raise the potential of the chassis above ground.
Unlike neutral, which code says is to be bonded to ground at only one point,
it is considered good engineering practice to "grid the ground", meaning
I would run an unspliced length of bonding wire from your box to the
Additional ground connections, such as a cold-water ground would provide
Get a grounding rod and bang it into the earth, then, use the
appropriate connector to fasten 1/4" solid flexible copper to ; fasten
the other end to the generators ground connector. Thats exactly what im
about to do to my portable generator.
I bought some ground rod this spring, and I seem to recall that they were
$8 for an 8' length. It's a simple steel rod, sharpened point and coated
I was surprised how inexpensive it was.
I don't think that these rods are especially susceptible to corrosion.
I believe that the steel core is a standard feature. Yes, they look like
but it's just a copper coating on the outside.
One of the rods in my home corroded and had to be replaced, but it took
nearly 30 years. I can handle $8 - $15 maintenance expense every 30 years
Life may be shorter if you have more acidic soil.
You can drive into pretty hard ground with a good sized sledge hammer, but
you are all done if you hit a hard rock. Lots of little firm taps works
big swings, with less chance of bending the rod. Work slow until you get
most of the
rod into the ground, than you can take bigger swings.
NEC code has a spec for the amount of resistance
that you must shoot for, I think it was something like 8 ohms. I did not see
description of how you actually measure it. If you can't get it on the first
rod, you have to
drive in a second. But, even if you don't do any better with the second, you
can stop at two.
I guess they figure if you don't get it after driving two rods, you chances
of doing better
with several is slim.
There are other possibilities, including buried mesh screens, and even
attaching to rebar inside the concrete of the structure. Most of the other
a bit of pre-planning or more work to install.
If you buy steel cored copper rods, also pick up some heavy duty clamps
brass or copper
clamps that are made for this purpose to attach your ground wire to the rod.
use #6 braided copper with no insulator.
Fancy version above isn't required for only a few jobs... a piece of
pipe with a heavy multi-layered cap is fine for pounding ground rods,
at which point many electricians finish the job using a hack saw. :-)
I bought 5/8" copper-clad steel ground rods for $8.xx earlier in the
year, but for the past couple of months or more they have been $13.xx at
the same store. The price of steel products has been skyrocketing,
allegedly because of the construction boom in China.
On 12/27/04 01:10 pm Bughunter tossed the following ingredients into the
ever-growing pot of cybersoup:
There are a couple of issues here.
Grounding the generator frame can be done via the Equipment Grounding Conductor
in the cable you connect it with (to the building electrode). Certainly driving
an additional rod when the ground thaws (~$10 plus about $5 worth of hardware)
is a safer approach but it will still have to be bonded back to the house via
The other issue is grounding the neutral. If your transfer equipment switches
the neutral you will need to ground the neutral in the generator.
In most cases the transfer switch only transfers the hot legs so you leave the
neutral isolated in the generator (as most portable generators are shipped).
This grounds the neutral via your main bonding jumper in the service panel.
NEC-2002 250.34(C) that requires the neutral to ground bond only if the
generator is a separately derived source. It is only a separately derived
source if the neutral of the sources are switched. See 250.20(D) FPN No1
Depending on how the generator will be used, it may not require a connection
to a grounding electrode system. The NEC states that it you will have
cord-and-plug connected equipment through the receptacles mounted on the
gen, then it doesn't require grounding of the frame. Also if this is the
case, then ensure that the manufacturer has bonded (connected) the neutral
and ground within the generator, as it is a separately derived source.
If the previous is not the case, then you must connect it to a grounding
electrode system. If your are serving a premises with a grounding electrode
system, it must be the same, meaning connect directly to it, or drive a rod
and connect the rod to the existing grounding electrode system. It must be
one grounding system, not isolated.
There are lots of other things to consider like how you will transfer the
loads to the gen, and such, but go carefully.
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