5kva dry transformer wiring

[finster1]

Need help...I need to certify some device installations that are wired
for 277v but I only have three phase 208 in the facility . Can I reverse wire a dry transformer 5kva and hook the secondary to the 208v line voltage
and get 277 out of the primary to run the tests? Anyone who can help would be greatly appreciated.:smile:

Finster
Licensed Electrical Contractor NJ

 

[brian john]

Not if the transformer is 3 phase 480 delta, 208/120 wye.

You can get a single phase transformer with 4 taps H1, H2, H3, H4 on 480 (primary) and 120/208 on the secondary and reverse wire that.

Or get a 208 delta to 480/277 transformer.

 

[LarryFine]

Not if the transformer is 3 phase 480 delta, 208/120 wye.

Finster, unless I'm mistaken, what Brian is saying is that 277 is a line-to-neutral voltage; 480 is the corresponding line-to-line voltage. To receive 277v, the 480v side of the transformer would have to be of a Y configuration, i.e., have 277v windings, which is rare on a primary.

However, his second statement . . .

You can get a single phase transformer with 4 taps H1, H2, H3, H4 on 480 (primary) and 120/208 on the secondary and reverse wire that.

. . . seems to me would only produce 277v on the 480v side by feeding 120v into the 208v side. Brian?

Or get a 208 delta to 480/277 transformer.

. . . which brings us back to the top of this post: the 480v side being of a Y configuration.

In any case, the transformer only need be 3-phase if the load is. What's important is having the voltage ratings you need for your source and your load.

Also, if you go 3 phase, do not connect anything to the supply neutral, even if the now-primary has an X-0 or H-0; let it float. (I learned that one here.)