disc location for exterior chiller fed direct from xfmr via transfer switch?

[malachi constant]

We are installing a new chiller to an existing facility. A couple things going on here:
1. When upgrading the utility transformer/connection cabinet, the customer would like to replace the CC with a custom combo CC/manual transfer switch. The intent of the transfer switch is to allow the entire facility - chiller and existing service - to be fed by a portable generator during an emergency.
2. To keep us from having to modify the existing service we want to feed the chiller direct from the transformer/conn cab/MTS.

I'm having trouble getting my head around the one line...
a) I assume a service disconnect is required ahead of the MTS (on the utility/line side) rated for both chiller and existing service combined. (In this case around 2000A.)
b) If I was doing this without the chiller - i.e. just feeding the service gear via the MTS - I would only need the disconnect noted above. But if that MTS/portable generator is to also feed the chiller, do I need to add two more disconnects, this time on the load side of the MTS, one for the chiller and one for the main service?
c) If the load side disconnects are required I would consider asking the customer to remove the chiller from the transfer switch. It would still be fed direct from the "connection cabinet" portion of the CC/MTS. Would this need a disconnect at the CC? I am thinking no, provided you put a disconnect at the chiller itself - if you took the MTS out of the equation, this (chiller directly fed from CC w/ no disconnect) is a code-compliant and fairly standard installation.

Other pertinent information:
* The run from CC/MTS to service equipment will be about 80', same for CC/MTS -> chiller.
* The chiller is located outside. It is around the corner in an enclosure, so would have a disconnect located at the unit. Tapping off the line side of the transfer switch without a disconnect there would not damage the chiller or transfer switch - only the unprotected exterior underground feeder. I suppose you could argue if the feeder melted it could take out the other equipment. I'm not really sure what code has to say about this.
* I plan to discuss with the electrical inspector, and the custom gear manufacturer, to get their thoughts, but would appreciate any insight you folks have.

Confusing situation. If a riser would help I can sketch one out and post it - let me know. Thanks!

 

[augie47]

I'm curious. What type of equipment is used for a MTS in the 2000 amp range ?

 

[GoldDigger]

Confusing, yes!
If the transfer switch is SUSE, (and how do you determine that for "custom"?) you might not need the additional disconnect ahead of it on either POCO or generator side, as long as the generator has its own OCPD.
Otherwise I would say that you need an SUSE disconnect on the POCO side of the MTS, but not necessarily on the generator side.

PS: Are you looking at an MTS with an intermediate position with both sources off? That might make it easier.
And don't forget the possible need for delayed break, early make on the neutral conductor if there is one and the MTS interrupts it.


Tapatalk...

 

[malachi constant]

See attached image for a better idea of what I'm trying to accomplish. (NOTE - assume all disconnects are fused.) My understanding is "Riser A" is perfectly legal per 240.21(B)(5) - that you can feed multiple services and equipment from one utility transformer/connection cabinet, without putting OCP at the CC. You would only need OCP as the feeder came into the building, or at the equipment if it serves exterior equipment and the feeder never enters the building envelope.

From there, I extrapolate out that "Riser B" (without the secondary disconnects) should be perfectly acceptable. The only change from A to B is a transfer switch, and a fused disconnect ahead of it to protect it. There should not be any need to protect the feeders, right?

 

[malachi constant]

If the transfer switch is SUSE, (and how do you determine that for "custom"?) you might not need the additional disconnect ahead of it on either POCO or generator side, as long as the generator has its own OCPD. Otherwise I would say that you need an SUSE disconnect on the POCO side of the MTS, but not necessarily on the generator side.

I'm using a local custom gear manufacturer. This is for a school district that has done several of these before with the disconnect / manual transfer switch combo to backfeed the service, and am just following their protocol (which was approved by electrical inspector and utility). I'm adding the wrinkle of feeding a new chiller off it, so as to avoid having to upsize and/or tie into the existing service. I agree that unless you can get a service entrance rated transfer switch, that a disconnect on the POCO side is required to protect it - that is my plan. And agree that as the generator will have an output breaker, there is no need for OCPD on the generator side of the transfer switch.

PS: Are you looking at an MTS with an intermediate position with both sources off? That might make it easier. And don't forget the possible need for delayed break, early make on the neutral conductor if there is one and the MTS interrupts it.

Good thoughts. Had not considered either of those. Thanks for the input!!

 

[augie47]

If your MTS and (possible) service disconnect are located outside, IMO, 240.21(B)(5) would still apply.

(Still curious as to where one finds a 2000 amp MTS)