electron

We are trying to size a generator for a warehouse, and these are the loads:

Three 7.5 Ton a/c units, 480V. each unit has two compressors rated
5.2 RLA, 44 LRA.

Two 277V. 20A circuits with 10 fluorescent lights (T-8, 6 lamps)

The owner wants to have a automatic transfer switch, I know we need a generator big enough to handle the start of the compressor, but is there a way we could delay the start of the second and third one?
I will appreciate any suggestions, thanks.

kbsparky

A load-shedding transfer switch would be one method.

Barring that, I'd use some time-delay relays on the control wiring with different values set on each HVAC unit, so they won't all try to start at the same time.

__________________
-KB

Life is uncertain -- eat dessert first!

wildleg

I agree with kb. phase loss monitors with adjustable restart times

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mbednarik

check with the HVAC co. I ran into some geothermal heat pumps a while back that had a random restart time so that two units would try to start at the same time.

electron

Thank you for all the replies, I just went back to the warehouse today and took some measurements and these is what I got:

Unit #1,

Starting Amps= 12A, after 6sec. will drop to 4A,

after 2 or 3 min. I guess the second comp. kicked in and it went up to 17A,

after 6 sec, it went down to 13.8A and it was stable at that until the

thermostat will cut off, then it just repeats the cycle. It did the same in all

phases with 2 or 3 amps of difference. I was king of surprised since the

data plate shows 44LRA, but I am not sure if I'm missing something.