Transfer switch and grounding

[JoeP]

I bought a small portable generator and had an electrician install a
manual transfer switch on my house.

A 30 amp 120V/240V twist lock cable goes from the genset to a receptacle
on the side of my house. Inside I can cut six circuits over to the
generator and isolate them from the line.

The electrician did not install a grounding rod for the generator
outside. Is the ground through the transfer switch to my house ground?

I was going to buy a grounding rod and pound it in the earth outside and
hook the generator's frame to that when in use. But I am concerned that
this will make a duel ground system when it is connected to the transfer
switch.

 

[Josepi]

You would only be able to tell by opening the connection boxes and looking.

Plug the generator in (not running) and run another extension cord from
inside the house to the generator location. Now take an ohm reading between
the ground pin on the extension cord and the generator case.


I bought a small portable generator and had an electrician install a
manual transfer switch on my house.

A 30 amp 120V/240V twist lock cable goes from the genset to a receptacle
on the side of my house. Inside I can cut six circuits over to the
generator and isolate them from the line.

The electrician did not install a grounding rod for the generator
outside. Is the ground through the transfer switch to my house ground?

I was going to buy a grounding rod and pound it in the earth outside and
hook the generator's frame to that when in use. But I am concerned that
this will make a duel ground system when it is connected to the transfer
switch.

 

[Josepi]

It's the same old multiple grounding issue. It always sounds good but a
nasty electrical fault in the rest of the home could prefer your new ground
and burn off that little #14 ground wire.


If you only connect the frame (chassis) of the generator to the
ground, I see no problem in having another ground even if it's
'extra'.
Make sure the frame of the generator in not already tied to a neutral
in the transfer switch.

George

 

[JoeP]

Josephi,

Good idea, I will try this. So the extension cord from the house
should NOT be one of the circuits that the transfer switch works with.
Then I test the resistance as you describe. If there is none, then
that means the ground for the generator (and case) is electrically
connected to my house ground -- all sharing the same.

I will check it tomorrow!

Thanks...

 

[Martin Riddle]

I bought a small portable generator and had an electrician install a
manual transfer switch on my house.

A 30 amp 120V/240V twist lock cable goes from the genset to a
receptacle on the side of my house. Inside I can cut six circuits
over to the generator and isolate them from the line.

The electrician did not install a grounding rod for the generator
outside. Is the ground through the transfer switch to my house
ground?

I was going to buy a grounding rod and pound it in the earth outside
and hook the generator's frame to that when in use. But I am
concerned that this will make a duel ground system when it is
connected to the transfer switch.

You have to check the NEC code on this.
I vaguely remember the ground is required if it’s a permanent
installation.

See this page...
<http://www.electrical-design-tutor.com/generatorgrounding.html>

I think you’re a "Non-Separately Derived System", you should be fine.

Also, another ground can cause a voltage loop on the ground line to the
generator.
(if its any sizable distance from the main neutral/ground bonding point)
This could cause other problems with GFI's and such.


Cheers

 

[Josepi]

GFIs do not measure, use or need a ground in any way. The work by measuring
differential current in the two current carrying conductors.

It can interfere with other items though and the NEC is a good thing if you
can find any specification to it. Grounding is a very complicated, poorly
understood field, even by your inspectors. Each one will give you a
different answer, in some cases, on grounding. Ask your local one for his
opinion.


You have to check the NEC code on this.
I vaguely remember the ground is required if it’s a permanent
installation.

See this page...
<http://www.electrical-design-tutor.com/generatorgrounding.html>

I think you’re a "Non-Separately Derived System", you should be fine.

Also, another ground can cause a voltage loop on the ground line to the
generator.
(if its any sizable distance from the main neutral/ground bonding point)
This could cause other problems with GFI's and such.


Cheers

 

[JoeP]

I checked this today.

Plugged the generator in to the transfer swicth. Generator remained
off. Had all circuits on LINE so the generator was isolated. Got the
extension cord and plugged it into the house and ran it out to the
generator. Switched my meter to continuity test and connected the
ground of the cord to the case ground on the generator.

Thus, when plugged and even with all switches in the sub-panel on the
LINE and not on the generator -- the generator case is grounded to the
house ground. I think I'm a-OK then!

Thanks again for the feedback and advice.

JoeP