Generator wiring

[dnbob]

In the case of using a 4 pole transfer switch for a 3 phase generator, would a grounding conductor be required in a non metallic raceway from the generator to the transfer switch? If not, how would the transfer switch enclosure be grounded, assuming all non metallic raceways?

The generator is bonded to the water service

Bob

[ January 23, 2005, 08:42 AM: Message edited by: dnbob ]

 

[bob]

Re: Generator wiring

When you transfer the neutral you will need to:
1. bond the generator frame and neutral terminal together.
2 Install a grounding electrode at the generator
and bond to the frame.
3. Install an EGC from the GEC to the transfer switch.

 

[Ed MacLaren]

Re: Generator wiring

This sketch may help illustrate Bob's good advice.

Ed

 

[bwilson]

Re: Generator wiring

Are you sure you wand to bond the neutral in both the gen set and the transfer switch with a grounding conductor ran with the phase conductors in PVC? Are you not creating a parralel path?

 

[bwilson]

Re: Generator wiring

Forget what I posted. Just looked at the diagram again.

 

[russ]

Re: Generator wiring

Thanks for the drawing Ed.

I just noticed something that's troubling.

This drawing is exactly the way it should be drawn.
All the bonding and equipment grounds are done properly. With the grounding electrode conductors tied to the same electrode, we still end up with the same parallel path as if the grounded conductor was never broke.
I'm starting to doubt that the breaking of the grounded conductor in the transfer switch is the solution I thought it was.

EDIT
I guess this is the same as two houses bonded to the same water pipe, and fed from the same transformer.

[ January 30, 2005, 06:31 AM: Message edited by: russ ]

 

[Ed MacLaren]

Re: Generator wiring

With the grounding electrode conductors tied to the same electrode, we still end up with the same parallel path as if the grounded conductor was never broke.

Russ,
I think what you are seeing in parallel in the sketch above is the grounding electrode conductors (blue) and the equipment bonding conductors (green). That is not a problem. It is neither hazardous or prohibited by code.

What is a code violation is any path that is in parallel with the grounded (neutral) conductor.

By switching the neutral, two completely separate systems are created, with regard to normal load carrying conductors.

Note - These examples show a single phase system, however, the grounding/bonding would be identical for a three phase system.

Ed

 

[russ]

Re: Generator wiring

Ed: My concern is that if both grounded conductors (the one at the generator and the one at the main) are bonded to the equipment ground, and the equipment ground is continuos between the generator and the main, it acts as a jumper between the two grounded conductors, as does the?main grounding electrode conductor.

It's made me think that in that type of installation breaking the tie between the two grounded conductors is futile.

 

[Ed MacLaren]

Re: Generator wiring

it acts as a jumper between the two grounded conductors, as does the main grounding electrode conductor.

What specific problem do you believe that will cause?

It's made me think that in that type of installation breaking the tie between the two grounded conductors is futile.

What do you believe is the reason behind the requirement to break the grounded (neutral) conductor in the transfer switch, when the generator neutral is bonded to it's frame?

Ed

 

[russ]

Re: Generator wiring

I'm not sure if it's really a safety problem, other than a bad neutral connection would cause a lot of current on the equipment ground.
It might even be the lesser of two evils

I thought the reason for breaking the "neutral" was to keep the neutral current from traveling in a long round about way back to the source on more than one specific path (that path being the neutral).

 

[bob]

Re: Generator wiring

Russ
You do not have to transfer the neutral. It is simpler to just transfer the phase conductors and leave the neutral alone. Pros and cons of transferring the neutral are argued but there is no real advantage IMO. If you do not transfer the neutral you will need to extend the system EGC to the frame of the generator and remove the neutral to frame bond. No ground rod is required.

 

[russ]

Re: Generator wiring

Hi Bob:

I have used that solution in the past. I'm not to sure how many generators come with a provision to isolate the neutral. The couple I've seen done were field engineered and altered