Odd Generator Transfer Switch Installation

[fmdell]

I am doing an initial evaluation of an installation of a manual transfer switch in a physical therapy facility. The owners don't want to go with a permanent standby system. The building is single phase and is fed underground by double 750mcm AL conductors into a CT cabinet in the basement. There are 3 panels fed from the load side lugs in the CT cabinet and through a trough. Two 200A panels are in the mechanical room and are stubbed out just of the trough. The third panel is on the first floor. That panel is fed through a 200A disconnect that is stubbed out of the trough.

Here is the issue. I need to feed the entire 1st floor panel and pull some circuits out of the basement panels. I can feed a 200A-util./100A-Gen. generator-ready load center from the disconnect (or just from the trough), and I can land the circuits moved from the basement panels in there. But I am not aware of any load centers that give me any way of taking the power out of that load center to feed the other panel. There are lugs for the wires from the power inlet box. There are also lugs for the power from the utility. But, there is nothing for feeding an additional panel directly. It would be great if there was some sort of generator ready load center with a set of lugs at the end of the buss bars, but I don't know any such panel.

I also have very little space. the wall is pretty full.

Any ideas? I've tested the draw from the panel on the 1st floor. I threw an ammeter on each leg set to record the highest draw. 32A on one leg was as high as it went. I'm tempted to go with a 100A breaker in the gen-ready load center to feed the upstairs panel, and then just use butt connectors to downsize the conductors so that they will fit in the 100A breaker.

Assuming that I end up feeding the upstairs panel as a sub panel out of the gen-ready load center, do I need to keep the 200A disconnect? I can't find a good NEC rule to know if the transfer switch is an acceptable disconnect. My thought is that it should be.

 

[augie47]

I would think your Generator/Utility panel would be rated as Service Equipment. If so, there is no need for the 200 amp disconnect ahead of it. As long as you are sure about the loads, I see no problem with your plan to use the 100 amp breaker

 

[fmdell]

Definitely seems like the easiest option, and I can definitlely use the space if I can lose the disconnect. I just have to go through the hassle of getting permission from the EU to get into the CT cabinet.

I'm going to stop on the way past their office tomorrow and hang an ammeter (with the hold feature turned on) on the one lead for the whole day of normal clinic operation and then do the same thing another day for the other leg. They have a good number of small devices with heating elements, whirlpools with motors and refrigeration units for ice packs, etc., and I can't count on the panel schedule as much as I would like to. If I check the load for a whole day on both legs and total the highest values, I'll feel pretty confident about it.

 

[augie47]

Double check with your supplier...most brands of panels will accommodate branch breakers larger than 100 amp.

 

[fmdell]

Good idea Augie