4 Wire system and without landing the Neutral

[don_resqcapt19]

Where I don't need the neutral for L-N loads immediately, I like to bond the N-G at the first legal opportunity, then not bring the neutral downstream to ATS's. It avoids the cost of the neutral, but it also avoids the age old argument for a 4 pole ATS, which is should the neutral be open transition, or overlapping (closed) transition switching.

But you have to provide a supply side bonding jumper which will be the same size.

 

[tom baker]

The advantage of a 4 pole ATS or MTS is that the neutral is a current carrying conductor and you dont want neutral current feeding back from the Genset to the Utility Transformer or vice versa. as it would with a 3 pole ATS or MTS with a solid unswitched neutral. Its a safety thing.

And the neutral current goes back to its source, either the utility or generator. There will be no backfeeded, and its not a safety issue, there are millions of generators with non switched neutrals, its allowed in the NEC.

If you feels its a safety issue, submit a change to the 2020 NEC. I am not trying to be smart here, and being very respectful of your opinion.

 

[capybara]

There is nothing dangerous about a non SDS set up. How do you back feed the utility with your generator using only the neutral?
Answer is, you can't.

The neutral is a current carrying conductor.
Depends where it is bonded to ground. If its bonded N-G at the ATS or MTS, no problem.
If you have a 3 pole ATS or MTS, and its not bonded N to G there, if its switched to another source (for ex., another generator, or another TP&N feed),
you may be backfeeding the gen neutral (or the other source neutral) while its being serviced, which is why this is never done here.
It simply is not best practice, although legal.
If it was best practice, why would millions of us spend extra $ on 4-pole ATS or MTS?

 

[ActionDave]

The neutral is a current carrying conductor.

It is one CCC. In order to have a complete circuit you need at least one other CCC at a different potential.

Depends where it is bonded to ground. If its bonded N-G at the ATS or MTS, no problem.

If the utility neutral and generator neutral are both bonded at the service on the building then it cannot be bonded in the ATS and it's no problem either.

If you have a 3 pole ATS or MTS, and its not bonded N to G there, if its switched to another source (for ex., another generator, or another TP&N feed),
you may be backfeeding the gen neutral (or the other source neutral) while its being serviced, which is why this is never done here.

Conductors at the same ground potential can't back feed one another. If I take three batteries and tie all the negatives together and hook them up to one ground rod where it the backfeed?

It simply is not best practice, although legal. If it was best practice, why would millions of us spend extra $ on 4-pole ATS or MTS?

A non-SDS is the best practice. That is why it's the most common. Except for systems using ground fault protection I don't know why someone would spend extra money on a four pole transfer switch. They can cause problems if the neutral breaks to early or makes too late. And I don't think it is millions that do. I think the the number of non-SDS generators in service right now outnumber SDS generators by at least a million.

 

[ron]

But you have to provide a supply side bonding jumper which will be the same size.

fine; but the amount of that conductor is within that first disconnect enclosure. No need to run it with the downstream feeders.

 

[Flapjack]

But you have to provide a supply side bonding jumper which will be the same size.

Not if your generator has a breaker. You would only have to provide an equipment grounding conductor to the transfer switch.

If the generator doesn't have a breaker, then you are right that you would install an SSBJ, but you'd still save money because you don't have to pull a neutral.

If you pulled a neutral, you'd still have to have an SSBJ or an EGC as part of the circuit.

 

[don_resqcapt19]

fine; but the amount of that conductor is within that first disconnect enclosure. No need to run it with the downstream feeders.

When I posted that, I was really thinking of a transformer with the bonding at the transformer and a remote first disconnect.