dual speed motor

[thunderbolt]

how to size a breaker for a 100 hp,3 phase,. 480v, dual speed motor without nameplate data. Existing piece of equipment originally on a 250a adjustable circuit breaker and 125a fuses fed by 2/0 wire. What will an inspector need to see as the nameplate is obscurred, and based on 430.52(4) I am not sure how to justify this to inspector or based on table
430.250 , 125% of 124 amps=155 amps, next size up, 175 amp breaker. Thank you for your attention and assistance , much appreciated.

 

[kwired]

how to size a breaker for a 100 hp,3 phase,. 480v, dual speed motor without nameplate data. Existing piece of equipment originally on a 250a adjustable circuit breaker and 125a fuses fed by 2/0 wire. What will an inspector need to see as the nameplate is obscurred, and based on 430.52(4) I am not sure how to justify this to inspector or based on table
430.250 , 125% of 124 amps=155 amps, next size up, 175 amp breaker. Thank you for your attention and assistance , much appreciated.

First, is the 100Hp the rating for high or low speed? Low speed most likely has less Hp rating, and may need different overload setting for each speed.

Where are you getting 125% from? Conductors for a 100 Hp motor are to be 125% of FLA which gives you a min ampacity of 155 but the short circuit and ground fault device can be up to 250% if an inverse time breaker or even more if it will not hold during starting. It is common to see 200 amp breaker supplying a 100 HP motor though it could easily be a 300 amp breaker before you get into the permission to increase it because it will not hold during starting.