Counting current carrying conductors

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brother

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Well i ran into another 'i dont derate, and im gonna stuff this pipe as much as i can' project left by someone else.

I know some people dont derate, but i wanted to be sure i was counting the wires right. This a 3 phase 4 wire Y system, 120/208. there are 12 ccc in this pipe as i originally counted. Aparrently they ran 2 full boats and then added 2 more circuits with its neutral (2 hots and 2 neutrals). It also had the 2 pole 208 (black and red) circuit as well.

I wanted to be sure that counting the 2 pole 20 amp 208 (phase to phase) there, is correct?? Even though those phase cancel each other. I do count them in the current carrying scheme right? its late, just double checking myself.

Also the people that previous installed these never derated anything, so there are still on the 20 amp breakers with #12. So far no melt downs though. I reread 310.15 (4)(a) Neutral Conductor and started second guessing myself, i do still count all the neutrals right??
 
Let me see if I follow you:

2 - 3-pole breakers 6ccc
1 - 2-pole breaker 2ccc
2 - 1-pole breakers 4ccc
equals to 12ccc?

That's what I would come up with.
T310.15(B)(2)(a) 10 - 20ccc 50%

T310.16 #12thhn = 30 amps derate to 15 amps
#10thhn = 40 amps derate to 20 amps

brother said:
Well i ran into another 'i dont derate, and im gonna stuff this pipe as much as i can' project left by someone else.
Click to expand...

Looked at a job today. 27ccc in one conduit.
 
Minuteman said:
Yes, but it was just a L---O---N---G series of 24" sections of pipe connected together. :D
Click to expand...


Let's see. 30' ? 24" = 15

Yep that's one 15 segment nipple!:D
 
Chamuit said:
Let me see if I follow you:

2 - 3-pole breakers 6ccc
1 - 2-pole breaker 2ccc
2 - 1-pole breakers 4ccc
equals to 12ccc?

That's what I would come up with.
T310.15(B)(2)(a) 10 - 20ccc 50%

T310.16 #12thhn = 30 amps derate to 15 amps
#10thhn = 40 amps derate to 20 amps



Looked at a job today. 27ccc in one conduit.
Click to expand...


Ok let me try to clarify, All the breakers are single pole 20 amp, except for 1, and its a two pole 20 amp. So when i say a 'full boat' Im saying 3 hots (black, red, blue) and 1 (shared)neutral. These are single pole breakers. By the way, this is 3/4 conduit.

edited for clarity
 
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Brother, the neutral (s) with the full boats do not need to be counted. So

A,B,C, and N equal 3 CCC. I'll look for the code after I close this.

edit to add: 310.15(B)(4)
 
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benaround said:
Brother, the neutral (s) with the full boats do not need to be counted. So

A,B,C, and N equal 3 CCC. I'll look for the code after I close this.
Click to expand...

I suppose i always took the 'conservative' method in counting, because ive seen people put in more computers and other 'nonlinear' loads. I read 310.15(B)(4)(c) and im not sure what the code considers a 'major portion' of the load.

Alot of the loads are for refrigerators, freezers, and there other circuits for receptacles (microwaves) etc. Isnt some microwaves considered non linear?? im not much of an electronics guy.
 
Brother, 310.15(B)(4)(A) not (C) I should of added that in the first place.

As far as nonlinear loads, computer equipment is the main contributer.
 
benaround said:
Brother, 310.15(B)(4)(A) not (C) I should of added that in the first place.

As far as nonlinear loads, computer equipment is the main contributer.
Click to expand...

Ok, i read part (a) the first time and it just seems like that with the possibility of varying loads, that I needed to count the neutral because of (c).

Ive read (b) about the 3 wire cinsisting of 2 phase wires and neutral of a 4 wire, 3 phase wye connected system. So if you have just A, B, phase or A, C phase, or B ,C phase and a neutral then its 3 conductors??
 
brother said:
Ok, i read part (a) the first time and it just seems like that with the possibility of varying loads, that I needed to count the neutral because of (c).

Ive read (b) about the 3 wire cinsisting of 2 phase wires and neutral of a 4 wire, 3 phase wye connected system. So if you have just A, B, phase or A, C phase, or B ,C phase and a neutral then its 3 conductors??
Click to expand...

You got it.
 
If you look at Chamuit's calc you'll see that you have 12 CCC's without counting the two neutrals of the MWBC's. Even if you did count them (for serving non-linear loads) it wouldn't change you derating since 14 CCC's would still require a 50% adjustment.
 
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