3 Pole Vs. 4 Pole ATS

[infinity]

We have a job where the ATS's were installed as 3 pole instead of 4 pole so they do not switch the neutral. According to what we're being told this is a POCO requirement because they stated that there could be a "backfeed" on the neutral while the generator was providing power. Sounds questionable to me since both the normal service and the generator are connected to the same building GES and are therefore not completely isolated from each other. Is this a valid reason for wanting 4 pole ATS devices?

 

[iwire]

We have a job where the ATS's were installed as 3 pole instead of 4 pole so they do not switch the neutral. According to what we're being told this is a POCO requirement because they stated that there could be a "backfeed" on the neutral while the generator was providing power. Sounds questionable to me since both the normal service and the generator are connected to the same building GES and are therefore not completely isolated from each other. Is this a valid reason for wanting 4 pole ATS devices?

Absolutely not.

1) Three pole or not the neutrals remain connected to the utility via the GECs.

2) Current needs a circuit to flow on, one conductor is not a circuit.

The only argument I know of for four poles is when there is GFP protection involved and under certain conditions this could be a problem.

 

[Ingenieur]

Never heard of this requirement
usually they maintain this coonection

only scenario
util fault
raises X0 by fault current x gnd Z
usually very small
but if high enough the N/G to earth potential could allow current to flow thru what ever completed the loop

but on the sec of a xfmr can't see any magnitude

 

[texie]

We have a job where the ATS's were installed as 3 pole instead of 4 pole so they do not switch the neutral. According to what we're being told this is a POCO requirement because they stated that there could be a "backfeed" on the neutral while the generator was providing power. Sounds questionable to me since both the normal service and the generator are connected to the same building GES and are therefore not completely isolated from each other. Is this a valid reason for wanting 4 pole ATS devices?

It's pure nonsense from a technical perspective as I'm sure you already know. I would be asking if they have this documented in their terms of service or is this just some low level service planners take on it.
If they feel this way about a simple ATS installation, they must wet their pants over a grid tie system.

 

[pv_n00b]

Sometimes to POCO requirements is just their requirements and there is no technical reason for it. I have found I really can't successfully argue with the POCO about what they have decided they want. Last time I tried it took over 2 years to get them to accept something, and most people don't have that kind of time.

Having said that from an NEC point of view switching the neutral is the difference between a generator being a separately derived system or not. If the grounded conductor is not switched it's not a separately derived system. NEC 250 has a lot to say about how to treat separately derived systems that you don't need to worry about if you don't switch the grounded conductor.

 

[tom baker]

Neutral current goes to its source, the generator when its running.

 

[chris kennedy]

Neutral current goes to its source, the generator when its running.

That's it in a nutshell.

 

[kwired]

Neutral current goes to its source, the generator when its running.

That and you need a second conductor of the system connected before there can be any current to flow.

 

[GoldDigger]

That and you need a second conductor of the system connected before there can be any current to flow.

Which is why there can be problems with not opening the neutral when there is a separate ground to neutral bond on each source. Neutral plus EGC makes two wires.

 

[roger]

There's an echo in here.

Roger

 

[kwired]

Which is why there can be problems with not opening the neutral when there is a separate ground to neutral bond on each source. Neutral plus EGC makes two wires.

Now enter NEC and separately derived vs. non separately derived. If bonded at the generator it is separately derived and you must switch the neutral in the transfer equipment.