XFMR Primary & Secondary Ampacity

[yesterlectric]

Want to get a second opinion. I always thought that per article 450, you generally could size the overcurrent protection on primary and secondary of the xfmr at values above its full load KVA amps; but you still had to protect the conductors between the xfmr and the overcurrent device in accordance with their ampacity. So if you size the breaker at for example 150% of xfmr KVA, the conductors have to be of a size compatible with that breaker, not just sized per the xfmr KVA. Always how I thought it should be done but I have someone else insisting there’s no need to do this and you can simply size the conductors per the xfmr KVA and the breakers as per the allowances in article 450.

Sorry I’m not in a place to cite code specific references right now.

 

[david luchini]

Want to get a second opinion. I always thought that per article 450, you generally could size the overcurrent protection on primary and secondary of the xfmr at values above its full load KVA amps; but you still had to protect the conductors between the xfmr and the overcurrent device in accordance with their ampacity. So if you size the breaker at for example 150% of xfmr KVA, the conductors have to be of a size compatible with that breaker, not just sized per the xfmr KVA. Always how I thought it should be done but I have someone else insisting there’s no need to do this and you can simply size the conductors per the xfmr KVA and the breakers as per the allowances in article 450.

Sorry I’m not in a place to cite code specific references right now.

You are correct. The conductors need to be protected by the overcurrent device.