Transformer Protection Question

[adamscb]

Hey guys,

I have a 0.5 kVA, 480-240V single-phase transformer that's being protected by a 2 AT fuse on the primary. Is this a transformer protection issue? According to Table 450.3(B), the maximum rating of the OCPD on the primary is 167% of the primary current (currents less than 9 amperes).

My calculations:

Ip = 500VA / 480V = 1.04167A

1.04167A * 1.67 = 1.73958A, which is less than 2A (fuse rating)

Question remains: is this a transformer protection issue, or is there some kind of "round-up rule" for XFMRs?

 

[david luchini]

Hey guys,

I have a 0.5 kVA, 480-240V single-phase transformer that's being protected by a 2 AT fuse on the primary. Is this a transformer protection issue? According to Table 450.3(B), the maximum rating of the OCPD on the primary is 167% of the primary current (currents less than 9 amperes).

My calculations:

Ip = 500VA / 480V = 1.04167A

1.04167A * 1.67 = 1.73958A, which is less than 2A (fuse rating)

Question remains: is this a transformer protection issue, or is there some kind of "round-up rule" for XFMRs?

No, there is no round up rule, but there is no protection issue with this installation either.

See T450.3(B) Primary Current Less than 2 Amperes.

 

[adamscb]

Homer Simpson's "D'oh"!

 

[templdl]

Hey guys,

I have a 0.5 kVA, 480-240V single-phase transformer that's being protected by a 2 AT fuse on the primary. Is this a transformer protection issue? According to Table 450.3(B), the maximum rating of the OCPD on the primary is 167% of the primary current (currents less than 9 amperes).

My calculations:

Ip = 500VA / 480V = 1.04167A

1.04167A * 1.67 = 1.73958A, which is less than 2A (fuse rating)

Question remains: is this a transformer protection issue, or is there some kind of "round-up rule" for XFMRs?

Do you have a secondary fuse? If so it is the protection that protects the transformer from being overloaded. The primary fuse is for short circuit protection to take the transformer off line in the event the transformer fails such that it does affect the upstream distribution system.