3 pole transfer switches in series

[Live2learn]

I have a 4w+G system in which generators and utility feed a common 3P automatic transfer switch. The load then goes to a 3w+G switchboard and then to another 3P transfer switch.

The utility is 2000kVA OA, 12470 pri Y 480/277v sec and the Generators are connected Y through a 3 pole transfer switch. The Gen's are not a seperatly derived system. I know if you have multiple switches in a row that you want to switch the neutral, but what if my new switch is 3W+G with no neutral connection?

The current will not have parallel paths due to the fact the new system is without a neutral and having multiple 3P switches in row would not be an issue if the load is 3W+G - correct?

 

[waross]

The controlling issue is "Only one connection between the neutral and ground". I have investigated and repaired several installations with switched neutrals where for one reason or another the neutral went open and expensive damage was done. My first inclination is to never switch a neutral.
Yes, I know that there are some installations where the neutral must be switched. I only do so after I make a good attempt to arrange the installation so that the neutral may remain solidly connected through the transfer switches.
If you are able to comply with the "One connection to ground" condition you may use three pole transfer switches even with four wire systems feeding line to neutral loads.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

Yes.

Rafiq Bulsara

http://www.srengineersct.com

 

[alehman]

3W or 4W can be accomplished with 3P switches as stated above. Where things get tricky is if you need ground fault protection with 4W distribution. In that case the neutral sensors usually have to be downstream of the ATS's.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[jghrist]

It gets tricky if the generator and the utility service are not close to each other. With the neutral grounded only at the utility service, there can be a large impedance for ground faults when running on the generator. Ground fault current has to go to the service and then from the service to the generator through the neutral.