SeanJo
Member
- Location
- Houston, TX
A job I am helping on required a step-up transformer due to someone ordering the wrong equipment. The service to the building is 3phase 120/208v Y, and the new CRAC unit requires 480v 3ph. It was calculated that adding a step-up transformer would be cheaper than reordering the new CRAC unit :roll:. After wiring the transformer and starting it up, we tested voltage to be sure everything came out alright. The readings were as follows:
Primary:
A to grnd-120 A to B-208
B to grnd-120 B to C-208
C to grnd-120 A to C-208
Secondary:
A to grnd-277 A to B-480
B to grnd-277 B to C-480
C to grnd-240 A to C-480
It's also worth noting that we placed a jumper from X0 to the transformer grounding lug, even though the loads coming off of the transformer are going to be strictly 3phase Motors. Can anyone enlighten me as to why the C phase to ground voltage would be different when all coils were tapped at the same location(lug 3)? I wish I could have tried swapping 2 of the coils and seeing if it was only an issue with X3, meaning it could be an issue with the transformer itself, but it was the end of a long day and the system will not be started and operational until next week. Anyone with ideas or experience in this type of situation?
Primary:
A to grnd-120 A to B-208
B to grnd-120 B to C-208
C to grnd-120 A to C-208
Secondary:
A to grnd-277 A to B-480
B to grnd-277 B to C-480
C to grnd-240 A to C-480
It's also worth noting that we placed a jumper from X0 to the transformer grounding lug, even though the loads coming off of the transformer are going to be strictly 3phase Motors. Can anyone enlighten me as to why the C phase to ground voltage would be different when all coils were tapped at the same location(lug 3)? I wish I could have tried swapping 2 of the coils and seeing if it was only an issue with X3, meaning it could be an issue with the transformer itself, but it was the end of a long day and the system will not be started and operational until next week. Anyone with ideas or experience in this type of situation?
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