Primary Overcurrent Device Rating

[Squantum]

Here is a problem from Mike Holt's prep book, I hope someone can explain this to me.

Q:What’s the maximum primary overcurrent device rating for a 750 VA, single-phase, 480V transformer?

A: I Line = 750 VA/480V
I Line = 1.56A
Protection = 1.56A x 3.00 (Table 450.3(B))
Protection = 4.68A, 4A, [240.6(A)]

So they are looking for the maximum primary overcurrent device rating which is 4A.
My question:If 4A is max, what size fuse would you use?

Thank you

 

[iwire]

If the max size is 4 I would install a 4.

 

[Squantum]

Thanks for your reply, however, a 4A fuse is not a standard fuse,and I guess that's where I got lost. I am so use to selecting from 240.6 (A)

 

[iwire]

Thanks for your reply, however, a 4A fuse is not a standard fuse,and I guess that's where I got lost. I am so use to selecting from 240.6 (A)

Ahh, I see what you are getting at.

 

[don_resqcapt19]

Thanks for your reply, however, a 4A fuse is not a standard fuse,and I guess that's where I got lost. I am so use to selecting from 240.6 (A)

There is no permission, in this case, to round the OCPD up to the next standard size. The 300% is a hard limit that cannot be exceeded.

 

[steve66]

4 amps isn't listed as a standard size in 240.6, but it is commonly available, and non-standard sizes are permitted per 240.6.

I'd say the answer is 4 amps unless something in the question specifically says to use a standard size.