Here is a question for someone who knows the code.
I will be installing a generator aboout 60 feet from my home. Could
someone tell me what code requires for grounding it?
Do I put in a grounding rod/rods at the generator site or run its ground
wire to the panel in the house? (It seems that the former could cause a
ground loop and the latter would allow for some potential (voltage) between
the generator and the adjacent earth.)
I BEL:IEVE you do ground rods at the generator bonded to a nice heavy
line connected to the panel so ground loops cant occur.
this is kinda a leftover of my dish install days where bonding all
grounds was AAA+++ IMPORTANT
The generator should have a grounding point specified. This should be
attached to an 8 foot grounding rod. The ground connection on the
output plug should be connected to the ground at the electrical panel in
Thanks for the reply.
The generator will be for powering the house. The house panel will be
back-fed through a 240V breaker with a mechanical interlock preventing the
backfeed breaker and the main breaker from being turned on at the same
I am not sure what you mean by "bonded".
it is not. (non-bonded). It should say on both the generator and manual.
If you have a unbonded generator you are all set. Your generator is
grounded through the breaker box, and must not be grounded independently;
the ground loop you referred to.
If you have a bonded generator you have a problem. The generator must be
grounded, and the neutral connection on your main feed must be switched
along with the hots; again to prevent loops.
I don't have it saved any more, but there is a wonderful website from a
Canadian distributor that explains all of this in extreme detail with
diagrams; but I gave you the heart of it.
If your interlock switch disconnects the neutral from the mains input, you
will need to have or make your generator ground bonded to the neutral line.
If your interlock only switches the two hot lines and keeps the neutral
connection intact you want your generator without the ground bonded to the
neutral line. Remember the house neutral should be bonded to the ground once
in your service entrance switchbox.
That's why generators used in this manner need to have a bond link, a
physical, removable bar that connects the generator frame to the
generator neutral. When purchasing a generator, keep in mind that some
generators do not have a removable bond link.
In your case, since you are not switching the generator neutral in the
"transfer switch", I would recommend connecting the generator as
1...Remove the bond link in the generator, which results in the
generator neutral being isolated from the generator frame.
2...Run a **4 wire** circuit from the generator to the main house
panel. (2 hots, 1 neutral, 1 equipment ground)
3...drive a ground rod (two would be better, at least 6 feet apart) at
the generator. Connect a #4 bare wire from the generator frame to the
ground rods AND to the equipment grounding wire that runs between the
generator and the house panel. There is usually a lug on the generator
frame just for this purpose.
4...at the main house panel tie the generator neutral and generator
equipment ground to the house main panel neutral busbar (which in turn
is connected to the house grounding electrode system (ground rod(s),
underground water line, etc.)
5...connect the hots to your mechanically interlocked breaker.
The above method will result in what is referred to as a non-separately
derived system. Hopefully, to avoid confusion, note that the ground
rods at the generator in the above are not technically required by NEC
since an equipment grounding conductor is ran to the generator.
HOWEVER, using the ground rods in this way at the generator, especially
since the main panel is some distance from the generator, ensures that
the generator frame stays at ground potential. Most engineers will
specify this method when connecting a non-separately derived system.
The other way to connect the generator is as a separately derived
system. In that case you would have to not only change your transfer
switch so that the neutral is switched, but you would also have to
install a subpanel with the equipment ground and neutrals isolated from
each other. In that case the ground rods at the generator would
absolutely be required by NEC and the generator bond link would have to
be installed to bond the "separately derived" neutral and equipment
Note that the generator neutral is bonded to the equipment ground at
one place _only_ in both cases.
One way to look at it is that with a separately derived system, a
separate system ground for the neutral MUST be established. In a
non-separately derived system, the generator neutral is grounded by the
normal electric supply grounding system and any ground rods at the
generator are merely supplemental to help keep the generator frame at
I hope this doesn't cause confusion, as the point of my post is to help
you understand the function of the ground rod in each case.
There is often alot of confusion over this. This is because there are a
few variables to the equation:
1) Do you have a switch neutral in your transfer switch?
2) Is the neutral in your generator bonded to ground?
3) Are the house and generator grounds connected? Or should they be
Depending on the circumstances there are various "Sets" or possible
soultions. Rather than me explain it, the best web sites I found was
Warmest regards, Mike.
OK, I've read all the responses to the op's question and I'm still
confused. I know the goal is to make sure there is a ground in place
before & after the transfer switch. But is there a problem if the
generator is grounded to a rod and also connected to the service
ground? When I googled "ground loops", almost all responses were in
relation to hum in audio/electronics rather than electrical
distribution. So you even if have a ground loop between the service
ground & generator ground with maybe 1-2 volts differential, does that
really make any difference for running lights, refrigerator, and maybe
a radio while on generator power?
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