Breakers size

[ohmhead]

Well question motor circuit 100 hp fla on name plate 111 amps 3 phase 480 volts no voltage drop needed .

wire 4/0 copper thwn-2
motor has a starter with overload protection
2 inch conduit rigid

What is the largest breaker protection you can put on this circuit just a general question to wire size to breaker size ?

wire size to breaker size !

 

[iwire]

Due to the various exceptions it is not really that easy to pin it down but ....

100 HP 460 volt motor.

Per Table 430.250 that motor has a load of 124 amps. (forget the nameplate FLA for breaker sizing)

Per Table 430.52

Max Non Time Delay fuse = 400

Max Time delay fuse = 225

Max Inverse Breaker = 350

Max Instanious breaker = 1000

 

[chris kennedy]

Max Inverse Breaker = 350

Max Instanious breaker = 1000

Where do these two multipliers come from?

 

[iwire]

Where do these two multipliers come from?

Per Table 430.52

Max Non Time Delay fuse = 400 amps

Max Time delay fuse = 225 amps

Max Inverse Breaker = 350 amps

Max Instantaneous breaker = 1000 amps

Plus I rounded up to the next standard size.

 

[kwired]

Well question motor circuit 100 hp fla on name plate 111 amps 3 phase 480 volts no voltage drop needed .

wire 4/0 copper thwn-2
motor has a starter with overload protection
2 inch conduit rigid

What is the largest breaker protection you can put on this circuit just a general question to wire size to breaker size ?

wire size to breaker size !

Motor branch circuits do not need wire ampacity to match the overcurrent device amps. Your 100 hp motor needs a minimum of 155 amp conductor but depending on what type of overcurrent device you have it could be rated well above that.

The conductor is still protected from short circuits and ground faults by the fuse or breaker and is protected by overloads by the overload protective portion of the motor controller.

 

[ohmhead]

Due to the various exceptions it is not really that easy to pin it down but ....

100 HP 460 volt motor.

Per Table 430.250 that motor has a load of 124 amps. (forget the nameplate FLA for breaker sizing)

Per Table 430.52

Max Non Time Delay fuse = 400

Max Time delay fuse = 225

Max Inverse Breaker = 350

Max Instanious breaker = 1000

Would it matter if it went thur a vfd drive or would this be the same iwire ?

 

[don_resqcapt19]

Would it matter if it went thur a vfd drive or would this be the same iwire ?

The feed to the drive must be sized based on 125% of the rated input amps to the drive. 430.122