Proper XFMR fuse for secondary

[Steelhead]

I understand when power is first supplied to a transformer there is a large in-rush current until the transformer reaches its normal magnetizing current. Does this large in-rush current affect the secondary? I am trying to figure out what type of fuse (that could handle the possible high in-rush current for a short time) I need to protect the secondary. My initial thought was that the in-rush current only affected the primary so you would choose a fuse rated for that, but what about the secondary?

 

[mayanees]

You are correct that the primary ocpd is the only device that sees the inrush.
Primary and secondary protection are governed by tables 450.3(A) or (B).

 

[templdl]

I understand when power is first supplied to a transformer there is a large in-rush current until the transformer reaches its normal magnetizing current. Does this large in-rush current affect the secondary? I am trying to figure out what type of fuse (that could handle the possible high in-rush current for a short time) I need to protect the secondary. My initial thought was that the in-rush current only affected the primary so you would choose a fuse rated for that, but what about the secondary?

No. The secondary OCPD does two things, if the transformer is sized to supply the load then the wire is also sized to carry the load but the ewecould be larger. Then the OCPD is sized toprotect the transformer. Should the wire be sized less than the rating of the transformer then your goal is to protect the wire which would be an unusual design and unlikely but not to be overlooked. But reference table 450.3(A) or (B) of the NEC as refered to previously should you have a copy.
But, as far as inrush is concerned the secondary OCPD does not see transformer inrush.

 

[Steelhead]

Thanks for all your help guys!