Town Park Shower Building Generator

[silurian]

I was asked to give an estimate for out local Town Park Shower building. It has a 400 amp Sq D QO load center with a 400 amp meter socket, back to back. No disconnect in between. Two sets of paralleled 4/0 4/0 2/0 feed the panel from the meter socket. Their main concern is having the well, which is protected at 70 amps, and the lights in the shower area on the generator. Also, the park office is connected to the same building, so the town foreman thought lights and the receptacles in the office would be good as well. Clearly, the requested generator load is not 400 amps, nor is the load of the entire building. Besides the well, it is LED lighting and general purpose receptacles. However, there is no room for a transfer switch inside the utility room. So the only option is an exterior "whole load" transfer switch. So, my question is: Is is code compliant to control and power one just one set of the paralleled conductors with the transfer switch and generator as long as the other set passes through the switch as well so the paralleled conductors stay together.

 

[charlie b]

Forget complying with code. What you described does not comply with physics. If you have some things connected to one wire and different things connected to a second wire, the two wires are not in parallel.

 

[GoldDigger]

If you are asking whether or not it is possible to transfer just some of the loads, at a subpanel level, while leaving other loads connected to the utility supply when it is down, the answer is yes.

Those two sets of loads would be in parallel when the ATS is in the utility position but the wires feeding them would not be parallel conductors as the NEC defines them (connected on both ends.)

Things to look out for would be to avoid mixing OCPD protected and unprotected (service conductors) in the same raceways.

You could also just use a whole building ATS and connect load shedding relays in the feeder and/or branch circuits which you do not want backed up by the generator.

Note that if any of the backed up loads (say interior lighting, for example) are considered mandatory safety loads there may be strict limits on separating those circuits physically from the optionally backed up or the unbacked circuits.

 

[steve66]

No, I don't think what your are suggesting would be code compliant. No telling how much current would actually be going through the ATS, and I assume the ATS would be rated for less than 400 amps.

I would just specify a 400 amp transfer switch, and enough generator for the entire load.

Or I would call out for a new subpanel on the outside of the building to supply the generator loads.

 

[kwired]

If you don't break all conductors of the parallel sets, the transfer switch is useless, you will not have isolation between utility and the generator regardless of which position the transfer switch is in. All you are doing is diverting where current can flow at any given time. I guess you would isolate the generator in the off position, but would be interconnected to utility in the other two positions.

 

[Dzboyce]

No.

besides all the previous replies, your 70 amp well pump is a 2 pole load. That well pump will either be a 5 hp or 7 1/2 hp 230 volt motor.

 

[steve66]

If you don't break all conductors of the parallel sets, the transfer switch is useless, you will not have isolation between utility and the generator regardless of which position the transfer switch is in. All you are doing is diverting where current can flow at any given time. I guess you would isolate the generator in the off position, but would be interconnected to utility in the other two positions.

That's true. He would be backfeeding the utility, which could be very dangerous for line crews.