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!

*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.

Jobs

1ph Genset and Transfer Switch Switching 2 Legs of 208Y/120

1ph Genset and Transfer Switch Switching 2 Legs of 208Y/120

(OP)
Looked at a facility that has 208Y/120 power throughout.

Their automatic genset is a 120/240 1Φ set that only powers selected circuits.

The way this is accomplished is by interrupting or transferring phases A and B before they hit the subpanel. Phase C is going straight from the utility-supplied breaker to the subpanel without interruption.

All loads on this circuit are 1Φ, so no risk of single-phasing any 3Φ motors.

But it occurs to me that under certain conditions, a heavy heating element from A-C or B-C could sufficiently energize C (reference neutral) to cause a hazard to personnel on line.

When utility returns but time has not elapsed for retransfer, voltages A-C and B-C could be wild and fluctuating.

Voltage of 208V equipment connected A-C or B-C would remain >120V during the duration of the outage.

I don't know where to look for the code violation here, but there must be one somewhere.

RE: 1ph Genset and Transfer Switch Switching 2 Legs of 208Y/120

I agree with your concern.
I don't believe that the code allows a panel to be fed from two sources let alone two sources that may be at differing frequencies.
How large is the genset? When I was doing a lot of generator work, it was common for sets above about 15 KVA to be re-connected and re-rated three phase sets.

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

RE: 1ph Genset and Transfer Switch Switching 2 Legs of 208Y/120

(OP)
I looked, it is a single phase only (4-lead) unit, with a matching single phase transfer switch.

I am going to work on them to see if we could possibly change the subpanel feeder circuits to single phase.

But it would be nice to have a code citation.

RE: 1ph Genset and Transfer Switch Switching 2 Legs of 208Y/120

I have only the Canadian Electrical Code in a .pdf file.
If you can gain access to the NEC in .pdf format do a search on "transfer".
The AHJ may support your position.

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

RE: 1ph Genset and Transfer Switch Switching 2 Legs of 208Y/120

(OP)
I guess 702.5 "inadvertent interconnection of normal and alternate sources" is as close as we may come to this one.

I found nothing else in the code under "transfer" that seems to apply.

RE: 1ph Genset and Transfer Switch Switching 2 Legs of 208Y/120

Thanks for the feedback John. Given the situation, I am sure that your AHJ will support your position.

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

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close