Motor disconnect size

O

OkieSpark

Member
Location
Oklahoma
Occupation
Electrician
When sizing a breaker or fuse for motors using table 430.52 you adjust using the corresponding percentages for your type of fuse or breaker. So let's just say I'm using 250% column. 430.110 also says disconnecting means not less than 115% for motors. So would I size my disconnect at 250% since it says " not less than 115%"? If not why and what should I go off of?
 
You size the fuses for the motor, then the disconnect must match the fuse size. So a fused disconnect with properly sized fuses will by default always exceed the 115% requirement. The reason the 115% rule exists is for when you have the disconnect DOWNSTREAM of the
motor branch-circuit short-circuit and ground-fault protective device, i.e. the local disconnect "within sight" of the motor.
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If the disconnect is only the motor disconnect, it does not have to have a rating greater than 115% of the motor FLA .
 
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The 115% is minimum. You would size the disconnect corresponding to the fuse selected byb430.52 with 430.110 taken into account
 
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