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Discussion Starter · #1 · (Edited)
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
 
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