[guitarboyled]

Please tell me if all is ok

I have a 37.5 kVA tranny [email protected]/120 (protected on the primary side only)

If I don’t know the actual full-load I have to size the OCPD on the primary this way:

37 500 / (480 x 1.732) = 45.1A

I could fuse at 45A

Bu I’m also allowed fusing at 125% of the nominal (rated) primary current:

45.1A x 125% = 56.4A

And because the rated primary current is above 9A I can round up to the next higher standard fuse size:

60A

Now if I do know the actual full load (let’s presume 30500 kVA or 36.7A) I’m allowed fusing for that load:

40A fuse

 

[micromind]

I've never seen a 37.5 KVA 480-120/208 transformer. Is it single phase? I suspect it is, and if so, it'd be 480-120/240. This makes a difference in protection.

 

[guitarboyled]

I've never seen a 37.5 KVA 480-120/208 transformer. Is it single phase? I suspect it is, and if so, it'd be 480-120/240. This makes a difference in protection.

I was making up an example but, I just checked the net, they do exist