NEC/ Overcurrent

[Stephen2awesome]

@Stephen2awesome How do you explain  #CI-I-69. where he asks largest allowable current for O/C device to protect 300kcmil, (TW) 60 degree Celsius, Aluminium Conductors in steel conduit feeding a 277V load. From table I get Ampacity as 195A. Now which option is true  for answer 180A or 200A and why. I thought 200A as it next higher level, but CI says 180 ( Does not explain). Your help is required here. Thanks

I think it is an error on their part. I asked about it back in September. 

 

[rg1]

I think it is an error on their part. I asked about it back in September. 

Thanks a lot. Lol. I was part of that discussion. I just wanted to double check if the group has become wiser after that. I myself updated my wisdom for that Motor OC thing during this time. 

 

[rg1]

I think not more than phenomenon is also applicable to Motor feeder  SCGF protection- 430.62.A?

 

[Omer]

can some one confirm which way to go for Motor feeder  SCGF protection

 

[Stephen2awesome]

I think not more than phenomenon is also applicable to Motor feeder  SCGF protection- 430.62.A?

So for this one, the protective device can not be greater than what is calculated in 430.52. If it's for 2 or more branch circuits fed by same feeder, then use the largest. also take into account the two exceptions. 

Then in 430.62 (B), it says if feeders have ampacity greater than what is required in 430.24, the rating/setting of the feeder OCPD shall be based on the feeder conductors.

 

[rg1]

So for this one, the protective device can not be greater than what is calculated in 430.52. If it's for 2 or more branch circuits fed by same feeder, then use the largest Plus FLA of others????. also take into account the two exceptions. 

Then in 430.62 (B), it says if feeders have ampacity greater than what is required in 430.24, the rating/setting of the feeder OCPD shall be based on the feeder conductors.

Thanks. IMHO it takes into account Setting calculations of the largest motor as per 432.52 Plus FLA of other motors. 

 

[Omer]

Thanks. IMHO it takes into account Setting calculations of the largest motor as per 432.52 Plus FLA of other motors. 

Still the question, after calculation done, which way to go?

I am thinking of going home.

 

[rg1]

Still the question, after calculation done, which way to go?

I am thinking of going home.

Hahha. Going home in good mood with a feeling of passing it. IMHO Go lesser side. 

 

[Stephen2awesome]

Thanks. IMHO it takes into account Setting calculations of the largest motor as per 432.52 Plus FLA of other motors. 

From what the code says, plus the sum of the FLC of the other motors of the group, then I would say yes.