ECN Forum Forums Code Related Discussion NEC & other Code issues Motors

When installing a motor...Shouldn't you rate the fuses at 125% of FLA and the overloads should be set to run at FLA? Thanks

Fuses have to handle LRA for a significant part of a second and higher than FLA for another second or so depending on load.
430.52 says you can use 300% of FLA for a single element fuse and 175% of FLA for a time delay fuse.

OL heater selection depends on Service Factor. See 430.32(A)(1)

[This message has been edited by Redsy (edited 05-01-2006).]

I agree with the other responses and will add that the OLs are based directly off the motors name plate rating.

The conductors, fuses or breakers are based on the HP and the info in Article 430 tables.

The conductors must be at least 125% of the table values

I do not recall an NEC minimum size for the fuses or breakers but common sense would say at least 125% and perhaps much higher for hard starting loads.