Table 310.15(C)(1) - More than 3 ccc

[designer82]

I have a situation where the contractor needs to install parallel sets of cables in an underground conduit for the service.

System is 120-208, 3ph-4w
Occupancy is Multi-Family residential

I have to derate for more than 3 CCc per Table 310.15(C)(1)

Question is do you use 4-6 or 7-9 for number of conductors?

I believe the neutral would not count as a CCC but Table 310.15(C)(1) says Number of Conductors (not Number of CCC conductors).

Of course, to complicate things the asterisk below the table says:
*Number of conductors is the total number of conductors in the raceway or cable, including spare conductors. The count shall be adjusted in accordance with 310.15(E) and (F).

 

[roger]

The title of 310.15(C)(1) is "More Than Three Current-Carrying Conductors"

 

[LarryFine]

Current-carrying conductors affects derating.

Total conductor quantity affects conduit size.

 

[augie47]

Your neutral may or may not count as a current-carrying conductor.

Here is a guide from one of the Forum members:

Note the bold, underlined portion.
Your neutral only counts where more than 50% of the load is nonlinear.

Here's some examples of when to count the neutral as a CCC:

208Y/120 volt system-different circuit types:

A)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C)- 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B)- In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C)- In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.

120/240 volt system-different circuit types:

D)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's

Notes:
D)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E)- In this circuit the neutral will only carry the imbalance between the two ungrounded conductors so the neutral is not counted as a CCC.

 

[charlie b]

Question is do you use 4-6 or 7-9 for number of conductors?

I can't answer this question. You didn't tell us the number of parallel sets of conductors. We can't make an educated guess because you didn't tell us the service amperage or the service transformer's KVA rating.

 

[don_resqcapt19]

The neutrals on the service will not be current carrying conductors for the purposes of ampacity adjustment for that application.
The neutrals associated with the feeders to individual units will be current carrying conductors for the purposes of ampacity adjustment, unless you are installing 3 phase panels in the units.

 

[designer82]

Thanks for you responses.

number of parallel sets of conductors: 2 Sets of Parallel Conductors. (meaning 2 conduits total, each conduit with 6 CCC's & 2 neutrals)
service amperage or the service transformer's KVA rating: Service amperage is 900A. Not sure of xfmr size (does it matter?)

Thank you @augie47 for the information. I'm confident the neutrals are not CCC's in this application (for the service only, not interested in dwelling unit feeders)

But where I'm hung up is that Table 310.15(C)(1) says "Number of Conductors*" not "Number of CCC Conductors"
So far I'm leaning towards 4-6 for (80% derate) rather than 7—9 (70% derate)

 

[augie47]

It might be helpful to go back and read the actual wording of 310.15(C)(1), not the Table heading.
It is a bit more explanatory that it's current carrying conductors.
In your case it appear you have six ccc's so you would derate the ampacity to 80% based on the type conductor.
For 900 amps I believe that would be a conductor with an ampacity of 281 amps.

 

[Jpflex]

The neutrals on the service will not be current carrying conductors for the purposes of ampacity adjustment for that application.
The neutrals associated with the feeders to individual units will be current carrying conductors for the purposes of ampacity adjustment, unless you are installing 3 phase panels in the units.

I suppose the neutral could be counted as a current carrying conductor if non linear loads are served. The service not having more than 3 ccc would not require bundling derating.

Also check ambient temp derating

 

[Jpflex]

I suppose the neutral could be counted as a current carrying conductor if non linear loads are served. The service not having more than 3 ccc would not require bundling derating.

Also check ambient temp derating

If service is paralleled you may have to derate