Three phase wiring question

Southside · April 04, 2024, 09:36:44 AM

I have a refrigerated sea can that was supposed to be a working unit when I picked it up a couple of years ago. It runs on 380V three phase which I can produce using a VFD and normally these things just plug into a receptacle on the ship.

My question is how does one know that the legs of the three phase are correctly wired on the supply side with these? The main wire plug goes into a whole control box and not directly into the compressor, and these run a scroll compressor which you really, really, don't want to run backwards, so it's not like a sawmill motor where you can bump it, swap two leads if the rotation is wrong and all is good.

Do these computer controlled systems simply adapt for the power phase arrangement? I mean how would every port, truck, emergency generator and ship all have their three phases arranged the same way? Is there a way to test for that arrangement?

I need to increase our walk in freezer space so the can is going from dry storage to cold storage, thus the latest project.

doc henderson · April 04, 2024, 10:17:31 AM

I am no expert and even my brother who used to wire 3 phase all the time had the luxury of being able to test it. He had to be careful with conveyors that had a mechanism to stop the loaded belt going backwards in case of power outage. I got the phase shifter, and it had the three legs initialed. the saw had different initials but if I traced those wires to the next connection, I found those had the same initials as the shifter. The initial connections went to 3 different motors, and it did not truly make the third leg until the big 10HP motor was rolling. there was a 110 leg for controls. this was 220 three phase. I went through 3 of these to find a good one, but it was only 330 bucks and no moving parts.

peakbagger · April 04, 2024, 12:38:02 PM

I have bought a lot of VF drives over the years and installed several big power generators at different places and every one had a requirement for a"bump check" where a coupling was broken to isolate the motor from the equipment and the motor was energized for a second to see which way it turned. The nice thing with VF drives were most of them had a feature that could be used to flip the rotation versus rewiring two motor leads.

moodnacreek · April 04, 2024, 01:30:16 PM

I am just a bump tester with 3 phase motors and can't help but when you get it figured out don't forget to color those wires.

Southside · April 04, 2024, 02:09:31 PM

With a scroll compressor everything is inside of a pressurized can which contains the refrigerant, so there is no mechanical connection one can break to bump test, that's the part that has me scratching my head.

SawyerTed · April 04, 2024, 02:30:58 PM

A phase rotation meter is NOT expensive and invaluable in such a situation. Less than $100.

You can determine connections and rotation direction with the meter.

Southside · April 04, 2024, 02:34:14 PM

AHHH - now there is a phrase that I was hoping to find. Do you know if I can test the motor side of the unit with such sorcery so I know both are correct? Or is there some place that a motor would be otherwise identified for correct rotation?

SawyerTed · April 04, 2024, 03:33:13 PM

You should be able to determine each phase winding connection and rotation with the meter.

You should be able to determine CW or CCW rotation on the motor then wire accordingly.