Ashu
Member
- Location
- Hunt Valley, USA
- Occupation
- Electrical Engineer
Hello,
I have a question regarding the sizing of the overprotection for feeder protection. In regular scenarios, motors will be matched to the actual load and then drives will be matched to the motors. However, in the machines I design, the servo motors are a lot higher size than the actual load requirements. Our machines employ a huge amount of Servo motors ranging from 10 amp to 98Amp each. However, the actual mechanical load is not that much but due to the peak torque requirements, the motors are selected of higher size. As I understand the overcurrent, short circuit and ground fault protection device needs to be according to the motor sizes. That to for induction motors we need to use table 430.250 rather than using motor nameplate data.
Recently, we measure the actual current of our machine which was 45% of the sum of actual rated FLA (motor nameplates) of all the continuous duty motors. We are looking now to adjust the rating of our feeder circuit breaker for future machines to consider the actual load on the servo motors rather than the nameplate data. However, NEC's article 215.3 mentions that the feeder's overcurrent protection can't be lesser than the 125% of the continuous load.
The question is: Does NEC allows to use the actual current for calculation purposes rather than using the nameplate data for Servo motors? I can't find any guidance on this situation. I will appreciate you thoughts or guidance. Thank you!
I have a question regarding the sizing of the overprotection for feeder protection. In regular scenarios, motors will be matched to the actual load and then drives will be matched to the motors. However, in the machines I design, the servo motors are a lot higher size than the actual load requirements. Our machines employ a huge amount of Servo motors ranging from 10 amp to 98Amp each. However, the actual mechanical load is not that much but due to the peak torque requirements, the motors are selected of higher size. As I understand the overcurrent, short circuit and ground fault protection device needs to be according to the motor sizes. That to for induction motors we need to use table 430.250 rather than using motor nameplate data.
Recently, we measure the actual current of our machine which was 45% of the sum of actual rated FLA (motor nameplates) of all the continuous duty motors. We are looking now to adjust the rating of our feeder circuit breaker for future machines to consider the actual load on the servo motors rather than the nameplate data. However, NEC's article 215.3 mentions that the feeder's overcurrent protection can't be lesser than the 125% of the continuous load.
The question is: Does NEC allows to use the actual current for calculation purposes rather than using the nameplate data for Servo motors? I can't find any guidance on this situation. I will appreciate you thoughts or guidance. Thank you!
