Make it make sense - OCPD Requirements for small transformers

[Tip DS]

Notice that when you choose to use primary AND secondary protection for a transformer, your primary protection maximum rating goes UP in all instances, except for small transformers. For those, you can use a big OCPD for primary-only protection, but if you're going to double up on protection, you have to use a SMALLER OCPD on the primary.

 

[wwhitney]

Two comments:

- Just because you choose to provide secondary protection doesn't mean you have to use the second line on the table. You can still use primary protection of up to 300% on a transformer with a current of 2A or less.
- For such a transformer, the second line still allows greater flexibility (primary protection at 600% or 400%) for some types of transformers because of Note 3.

 

[David Castor]

The simplest answer is that it doesn't have to make sense - it's in the NEC. Save your energy for something important.

 

[infinity]

This is one of the most poorly written code articles no wonder it causes a great deal of confusion.