More Than 3 Current-Carrying Conductors

[Aistobasbistoc9]

I am curious as to whether I should apply Table 310.15(B)(3)(a) to the load on a feeder for a bussed gutter system. I have 2 sets of (4)#350 and the bussed gutter is estimated at a demand load of 560A for a 600A service. The calculations for the demand load on the individual panels on this service were done per NEC. The continuous loads were calculated at 1.25, the non-continuous loads were calculated at 1.00, etc.

With that table, I would cap the full calculated demand load at about 488A (80%), correct? Do I assume that all 4 feeders are carrying current, including the neutral because it is most likely a non-linear load?

Thank you

 

[ronmath]

Ok, here we go, you seem to be referencing the 2014 NEC so we will go from there. First are the feeder conductors in conduit to feed the bussway? If so, then the table would apply. Second you must decide if 310.12(B)(5)(c) applies, where the majority of the load (greater than 50%) is nonlinear load. This will determine if you have 6 or 8 current carrying conductors if in a single conduit. If 6, it's 80%, if 8 it's 70% adjustment factor. You also don't call out the temperature rating of the wire but imply 75C. This is also likely to match the termination listing but would have to be verified. (2) 350 at 75C is 620A, *.8= 496A *.7=434A neither of which is large enough for your calculated load of 560A. To achieve your load of 560A you would need 560A /.8=700A /.7=800A, Parallel 500MCM or 600MCM respectively. Other solutions would be to provide 2 conduits and split up the runs so no adjustment for number of conductors is required unless the neutral is a CCC in which case you still have to apply the .8 factor to the runs requiring you to use 500MCM wire. Another option is to use a 90C rated wire and transition to larger 75C wire prior to the terminations. 350MCM @90C =350A X2 = 700A. 700A X .8 = 560A and would work according to your load calculations. 700 x .7 however would be a total of 490A and would not work unless you raised it to parallel 500's. Hope this helps and that I got it right as I am doing this in a hurry. If not in conduit but a nipple from the OCP, then no demand necessary in my opinion.

 

[infinity]

I am curious as to whether I should apply Table 310.15(B)(3)(a) to the load on a feeder for a bussed gutter system. I have 2 sets of (4)#350 and the bussed gutter is estimated at a demand load of 560A for a 600A service.

Thank you

What part of the system are you trying to calculate?

 

[chris kennedy]

Ok, here we go, you seem to be referencing the 2014 NEC so we will go from there. First are the feeder conductors in conduit to feed the bussway? If so, then the table would apply. Second you must decide if 310.12(B)(5)(c) applies, where the majority of the load (greater than 50%) is nonlinear load. This will determine if you have 6 or 8 current carrying conductors if in a single conduit. If 6, it's 80%, if 8 it's 70% adjustment factor. You also don't call out the temperature rating of the wire but imply 75C. This is also likely to match the termination listing but would have to be verified. (2) 350 at 75C is 620A, *.8= 496A *.7=434A neither of which is large enough for your calculated load of 560A. To achieve your load of 560A you would need 560A /.8=700A /.7=800A, Parallel 500MCM or 600MCM respectively. Other solutions would be to provide 2 conduits and split up the runs so no adjustment for number of conductors is required unless the neutral is a CCC in which case you still have to apply the .8 factor to the runs requiring you to use 500MCM wire. Another option is to use a 90C rated wire and transition to larger 75C wire prior to the terminations. 350MCM @90C =350A X2 = 700A. 700A X .8 = 560A and would work according to your load calculations. 700 x .7 however would be a total of 490A and would not work unless you raised it to parallel 500's. Hope this helps and that I got it right as I am doing this in a hurry. If not in conduit but a nipple from the OCP, then no demand necessary in my opinion.

With 75C terminations and 90C conductors you use the tables 90C column for adjustments as per the last sentence of 110.14(C).

 

[winnie]

I am curious as to whether I should apply Table 310.15(B)(3)(a) to the load on a feeder for a bussed gutter system.

You _never_ apply the derating for more than 3 current carrying conductors to the _load_. This calculation applies to the ampacity of the conductors.

The load is the load. This calculation doesn't change the load. This calculation helps you determine if the conductors are suitable for the load.

With that table, I would cap the full calculated demand load at about 488A (80%), correct? Do I assume that all 4 feeders are carrying current, including the neutral because it is most likely a non-linear load?

It is rare but possible for the neutral to count for derating. What are your loads?

Jonathan