Transformer Overcurrent Protection With oversized secondary conductors.

Status
Not open for further replies.
R

rknapp

Member
Location
Cleveland, Ohio, US
Is this legal?

60A Primary Protection -->
60A Conductors -->
25 KVA Transformer, 480V pri. - 120/240V sec. -->
200A Conductors -->
200A MCB within 15'

I am being told this is not legal because the secondary protection is >125% FLA of the transformer and therefore does not meet 450.3(B).

It is my opinion that the transformer is protected via primary only protection, 60A<125% FLA. And therefore secondary protection is not required for the transformer, only for the secondary conductors. Because the secondary conductors are rated for 200A, the 200A MCB adequately protects them.

Can this tranformer be protected w/ primary only protection? Therefore the secondary protection is allowed to be greater than 125% FLA of the Transformer???

THANK!!!
 
There is no code requirement restricting the size of the secondary protective device.
The code, 450.3, allows the primary device to be sized differently based on the size of the secondary device.
 
The transformer primary and secondary are protected by the primary OCPD as it is less than 125% of the rated primary current. Table 450.3(B). That only leaves the protection of the secondary conductors and as long as they are protected per 240.21(C) there is no code issue. How long are the secondary conductors?
 
With the secondary voltage of 120/240V, doesn't 240.21(C)(1) tell you that they are not considered to be protected by the primary overcurrent protective device?
 
samT said:
With the secondary voltage of 120/240V, doesn't 240.21(C)(1) tell you that they are not considered to be protected by the primary overcurrent protective device?
Click to expand...

In the original post, the secondary conductors are properly protected by a secondary OCPD per 240.21(C)(6).
 
samT said:
With the secondary voltage of 120/240V, doesn't 240.21(C)(1) tell you that they are not considered to be protected by the primary overcurrent protective device?
Click to expand...
\

If you are questioning Post #4, look closely... don said the primary and secondary (of the transformer) .. not the conductors.
 
Status
Not open for further replies.
Top