new generator, existing service

[bwyllie]

An existing facility is served from a exterior 2500KVA transformer with 480Y/277V on the secondary. The present neutral to ground bond is at the main switchboard. The client would like to install a Manual transfer switch outside that would get its normal power from the transformer and back up from a portable generator. A couple of questions:

1) Would the Transfer switch require a OCPD w/ gfi protection on the normal power side since this is the first termination of the transformers secondary conductors?

2) If yes to #1, then wouln't the neutral to ground bond need to occur at the transfer switch?

thanks

 

[ron]

Re: new generator, existing service

If the meter is on the secondary of the 2.5MVA xfmr, then the bond would need to ocur in the xfer switch. The xfer switch needs to have a service entrance rating. The GFI protection needs to be at the main switch.

 

[bennie]

Re: new generator, existing service

Is the generator intended to supply the entire load?

 

[bwyllie]

Re: new generator, existing service

yes, they have had trouble with utility power in this area and this property is primary metered.

[ December 04, 2003, 11:37 AM: Message edited by: bwyllie ]

 

[robrr]

Re: new generator, existing service

So, back to the original question, does the transfer switch need to have an OCPD w/ GFP on the normal power side?

 

[bennie]

Re: new generator, existing service

According to the IEEE Orange book, both the utility and generator source require overcurrent devices ahead of the transfer switch.

 

[bwyllie]

Re: new generator, existing service

That is what I recommended be done for this project. However, the client did not want to undertake the additional cost associated with this. They did not feel the neutral to ground bond had to be relocated.
The client went out and found another engineering firm to approve the design with OCPD at the transfer switch. Anything to save a buck. Must be a tough subject because it passed inspection as well.

 

[brian john]

Re: new generator, existing service

One Item I would check besides the required grounding and GFP required at this NEW service disconnect. Is.........Some large manual transfer switches are not load break rated. Both sources must be OFF for a manual transfer. That will not be possible with the design they have selected, if indeed they opt for a cheaper MTS.