×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

3 pole transfer switches in series

3 pole transfer switches in series

3 pole transfer switches in series

(OP)
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?

  

RE: 3 pole transfer switches in series

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

RE: 3 pole transfer switches in series

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.

RE: 3 pole transfer switches in series

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.
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources