Transfromer secondary conductors OCPD

[rhamblin]

I understand that secondary protection of transformers is not typical. What exactly would be secondary protection of a transformer. I know that 220.21 C allows for taps to be used, allowing us to eliminate secondary protection of a transformer and only provide protection of the secondary conductors.

In my mind the secondary protection would be a cb or set of fuses integrally mounted to a transformer.

Has anyone ever worked on such a transformer.

Here is a question that was brought up in my Master Prep class by the Teacher (which he could not find logical reasoning for), so I'll post it here to see if anyone can shed any light on the subject.

240.21 C 3 stipulates requirements for industrial installations (not over 25 feet long) and 240.21 C 6 stipulates for everywhere else (not over 25 feet long).

Why can you get by with a larger conductor size and overcurrent in other than industrial installations?

One of the stipulations for Industrial installations is that "conditions of maintanence and supervision ensure that only qualified persons service the systems".

I would think that in an "industrial environment" you would be able to get by with smaller ocpd and conductor sizes vs. a commercial store that has no supervision (possibly not even a maintanence person)

 

[raider1]

The biggest difference is that 240.21(C)(3) permits the secondary conductors to terminate at multiple overcurrent devices where 240.21(C)(6) requires that the secondary conductors terminate in a single overcurrent device.

Chris

 

[don_resqcapt19]

I understand that secondary protection of transformers is not typical. What exactly would be secondary protection of a transformer. I know that 220.21 C allows for taps to be used, allowing us to eliminate secondary protection of a transformer and only provide protection of the secondary conductors.

In my mind the secondary protection would be a cb or set of fuses integrally mounted to a transformer.

Has anyone ever worked on such a transformer.

Article 240 has absolutly nothing to do with the transformer overcurrent protection. Article 240 applies to the protection of the conductors and Article 450 applies to the required protection of the transfomer itself. You must satisfy the rules in both articles, however this is often accomplished with a single OCPD.

 

[steve66]

The biggest difference is that 240.21(C)(3) permits the secondary conductors to terminate at multiple overcurrent devices where 240.21(C)(6) requires that the secondary conductors terminate in a single overcurrent device.

Chris

I think Chris has it. I just wanted to add that it looks like if you're terminating on a single breaker or fuse, you can still use (C)(6) (and the smaller wire) in an industrial setting.

Edit: I type too slow, and Don snuck a post in there: I also agree with his comment.

Steve