Transfer switch - solid or switched neutral

[steve66]

Multiple questions, so I will number them so everyone can refer to the numbers.

First, does everyone agree with this:

(1) If one uses a three pole transfer switch (3P), the only Neutral to Ground bond (NGB) is at the normal source transformer secondary (which I will call XFMR-norm). The neutral is not bonded to the ground in the generator. Correct?

Next:

(2) If we have a 4 pole switch that switches the neutral (4P), then a NGB is placed at the XFMR-norm, and a NGB is placed at the generator. Correct?

Here is where it starts to get tricky:

(3) If there is an existing 3P transfer switch, can a 4P switch be added to the same generator? (I'm thinking in emergency mode, the 4P switch would get its NGB from the utility transformer through the 3P switch.)


(4) The generator feeds a transformer, that feeds the transfer switch. (So there is a transformer on the normal side and one on the emergency side.) Does one have to use a 4P switch with NGB at both transformers? Or can you use a 3P switch and only bond at the XFMR-norm?

(5) If a generator has two transfer switches, and it each one is connected to a different utility transformer, do all the transfer switches have to be 4P?

Thanks in advance:
Steve

 

[RUWired]

Multiple questions, so I will number them so everyone can refer to the numbers.

First, does everyone agree with this:

(1) If one uses a three pole transfer switch (3P), the only Neutral to Ground bond (NGB) is at the normal source transformer secondary (which I will call XFMR-norm). The neutral is not bonded to the ground in the generator. Correct?

Next:

(2) If we have a 4 pole switch that switches the neutral (4P), then a NGB is placed at the XFMR-norm, and a NGB is placed at the generator. Correct?

Here is where it starts to get tricky:

(3) If there is an existing 3P transfer switch, can a 4P switch be added to the same generator? (I'm thinking in emergency mode, the 4P switch would get its NGB from the utility transformer through the 3P sw


(4) The generator feeds a transformer, that feeds the transfer switch. (So there is a transformer on the normal side and one on the emergency side.) Does one have to use a 4P switch with NGB at both transformers? Or can you use a 3P switch and only bond at the XFMR-norm?

(5) If a generator has two transfer switches, and it each one is connected to a different utility transformer, do all the transfer switches have to be 4P?

Thanks in advance:
Steve

(1) Correct if the xfrmr is indoors, no if the xrfmr is outdoors.( if outdoors,the NGB needs to be brought to the first ocpd)

(2)
Correct

(3)
No because there will be no ground fault path from the generator to the 4p xrfr switch

(4)
If your feeding a xfrmr from a generator, you most likely won't need a neutral.your NGB will be on the secondary of the xfrmrs and it would be your choice as to where to make the NGB.Either at the xfrmr or the first ocpd .(But you will need to make the NGB at the generator)

(5)
Not sure

 

[dezwitinc]

Question #5
Just had this situation in Miami on a house with an out building and they required switched neutrals because the two transformers fed seperate services on the two buildings so I would say yes.

 

[steve66]

Thanks for the input, guys.

Steve