transformer secondary cond length

[frenchy]

Re;240.21C2&6 Is there any real big difference in the 10-25ft rules? Am I not seeing something?. It seems that either will work in most cases,if the 10ft is met, then up to 25ft seems easy to satisfy.

 

[don_resqcapt19]

The biggest is the ampacity of the conductor. For a 10' secondary conductor the ampacity of the conductor is only required to be 10% of the rating of the "overcurrent device protecting the primary of the transformer, multiplied by the primary to secondary transformer voltage ratio. For the 25' rule it must be at least 1/3 of rating of the "overcurrent device protecting the primary of the transformer, multiplied by the primary to secondary transformer voltage ratio." Also the 25' conductors must be terminated at a single OCPD with a rating not greater than the rating of the conductor. The 10' conductor must terminate on a device with a rating not greater than that of the conductors. While this looks almost the same, you can land the 10' conductors on a MLO panel and you can't do that with the 25' ones.
Don