Feeders are sized for not less than 125% of continous loads + non-cont. Overcurrent device for this is also sized for 125% of continous loads +non-cont. If I size the wire correctly and I size the OC to the next lower rating, I am not fully utilizing the wire size, but other than that, Why is this a safety rule?
We have the following Flywheel / Battery combo UPS unit;
Input 480 volt, 72 amps (per manuf.) & this includes efficiency
So 72x1.25=90A. We have the 90A bkr and the appropriate wire size
Secondary 208/120, so max. output is 50000/1.732x208=138.7
138.7x1.25=173.48. Wire is sized for 175 amp, but secondary breaker installed by manufacuter is 150 amp (our recommendation)
So the above is safe, but slightly underutilized.
My reasoning:
Acutal connected load is only around 30kVA and all that is not continous. So strictly per code we are OK. 50 kVA installation is for future loads. The reason we put the 150A bkr is, in case the facilities folks add loads in future there is a way to curtail random load additions. Any comments
We have the following Flywheel / Battery combo UPS unit;
Input 480 volt, 72 amps (per manuf.) & this includes efficiency
So 72x1.25=90A. We have the 90A bkr and the appropriate wire size
Secondary 208/120, so max. output is 50000/1.732x208=138.7
138.7x1.25=173.48. Wire is sized for 175 amp, but secondary breaker installed by manufacuter is 150 amp (our recommendation)
So the above is safe, but slightly underutilized.
My reasoning:
Acutal connected load is only around 30kVA and all that is not continous. So strictly per code we are OK. 50 kVA installation is for future loads. The reason we put the 150A bkr is, in case the facilities folks add loads in future there is a way to curtail random load additions. Any comments