One fuse for xfmr primary?

[Copperclad]

Hi folks,
I recently saw a 1ph. 5kva 480p/120s Transformer install, and noticed the 480v primary only had fused protection one one leg?
I started thinking maybe since the pri. windings were wired in series making this one 480v. loop that one fuse would suffice?
Im still thinking two fuses one on each leg would be the way to go,
Any thoughts?

 

[masterinbama]

Is the other leg the grounded leg of a corner grounded delta?

 

[Copperclad]

No,
The primary of the xfmr is 480v. 1ph.
They are tapping off of a existing 480/277 3ph. fuse block with the two line wires to get the 1ph. 480v primary.
One wire (L1) goes straight to the xfmr. and the other
wire (L2) is protected by a single fuse?
The system voltage throughout the whole plant is a basic 480/277 3ph. Y

 

[augie47]

My first thought was the same as masterinbama, but if it's not a grounded delta, then, I would think as far as the transformer is concerned, one fuse is enough, but both conductors would have to have protection per their ampacities. If the OCP ahead of the fuse block still protected the load side conductors, it would, IMO, not be a violation.
If one was trying to protect the transformer at 125% (13 amps) and the supply was, for instance, 40 amps, then a #8 wire, with one leg fused at 15 amps would be compliant.

 

[kwired]

Is it part of a listed piece of equipment?

If not there could be some tap rule violations also.

One fuse on one winding will protect from overcurrent but not ground faults on the unfused side.

 

[don_resqcapt19]

I can't put my finger on it, but for motor control circuit transformers (I don't think that is the case here with a 5kva) there was some type of code change a number of years ago that required two primary fuses. Older MCCs only used a single primary fuse. Maybe that same rule (the one I can't find) also applied to this transformer.

 

[WastefulMiser]

Single phase?

It could have been a 480/277P : 120S transformer.

 

[kwired]

Single phase?

It could have been a 480/277P : 120S transformer.

Reread post #3.

If it were 277 volt one fuse would be sufficient.