Supplementary protection

[Sitbck]

Do supplementary protectors (UL 1077) protect the wire? Is it ok to downsize a conductor if the proper branch rated protection is upstream of the supplementary protection?

For example if you have a 30amp branch rated protector up stream of a 10amp supplementary protector is it ok to size the wire according to the supplementary protector? Or do you size the conductor based on the load?

Thanks

 

[Dennis Alwon]

Do supplementary protectors (UL 1077) protect the wire? Is it ok to downsize a conductor if the proper branch rated protection is upstream of the supplementary protection?

For example if you have a 30amp branch rated protector up stream of a 10amp supplementary protector is it ok to size the wire according to the supplementary protector? Or do you size the conductor based on the load?

Thanks

If you are asking, for example, is it okay to run a 14 gauge wire with an OCPD of 30 amps as long as the supplemental protection in the equipment is 10 amps, then I would say yes.

This is a common usage for a/c units. The thermal protector in the unit will protect the wire from OCP. The breaker will protect from short circuit or ground fault.

Also, the wire must be sized to carry the load-- that is always the case.