How Many Current Carrying Conductors in Conduit

[jusme123]

Residential Setting
3- 220v single phase air conditioners and 3- 220v base board electric heaters

If 6 conductors are installed in conduit for air conditioning, and 6 conductors are also installed for baseboard electric heaters, how many current carrying conductors are in this conduit?

 

[petersonra]

not enough information.

 

[roger]

Are you trying to use 220.60 for the answer?

Roger

 

[Dennis Alwon]

All the wires are current carrying conductor's

 

[don_resqcapt19]

How would you ever get an answer other than 6 or 12 for this question?

As Bob said there is not enough information to give you a real answer, but unless you have some type of common control system for the air conditioning and the baseboard heat, I would say 12.

 

[jusme123]

Are you trying to use 220.60 for the answer?

Roger

I posted just for discussion, its an imaginary job at Bill Gates house

 

[Dennis Alwon]

Given the info- they are all current carrying conductor and you would have to count all for derating. Now can 220.66 come into play if there is no way to insure that the a/c and heat cannot cannot on together. That would be hard to do with baseboard and a separate a/c system.

 

[roger]

Dennis, you couldn't use 220.60 as basis to eliminate the number of CCC's in a conduit, it is only for calculating the total load for a feeder or service.

Roger

 

[broadgage]

If each of the 6 loads is a completly independant circuit then each load has two conductors, for a total of 12 conductors.
If the service is 3 phase, 4 wire delta, with 240 volts between each hot and any other hot, then in principle one could run a 3 wire, 3 phase branch circuit for the 3 heaters, and another similar circuit for the 3 A/C units.
That would be only 6 current carrying conductors.

In either event, some might argue that only the heating OR the cooling loads should be counted, but not both.
IMHO that is incorrect, Code allows one to consider only the larger of the heating or cooling loads when sizing the service, but I dont believe that there is any similar allowance for counting only one or the other when counting branch circuit conductors.

It would be entirely possible that following A/C unit repairs, that the electric heat would be turned to simulate hot weather and prove the repairs satisfactory.
Alternatively, one side of a large dwelling might need heating whilst the other needed cooling, with the conductors in the same conduit overheating might occur if the design was based on only one set being loaded at a time.

 

[Dennis Alwon]

I changed the poll to include 12 as the # of current carrying conductor's

 

[Dennis Alwon]

Dennis, you couldn't use 220.60 as basis to eliminate the number of CCC's in a conduit, it is only for calculating the total load for a feeder or service.

Roger

That is true. I was thinking that when you stated 220.60 that was where you wre going and I didn't think about it. Now in reality there should be something that would allow you to exclude conductors as current carrying conductor's if they are coincidental. A 3 way would be another example.

 

[roger]

That is true. I was thinking that when you stated 220.60 that was where you wre going and I didn't think about it. Now in reality there should be something that would allow you to exclude conductors as current carrying conductor's if they are coincidental. A 3 way would be another example.

Agreed

Roger

 

[iwire]

I don't see anything in this section that says we count more conductors as current carrying than can actually carry current at the same time.

310.15(B)(3) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a
Raceway or Cable. Where the number of current-carrying
conductors in a raceway or cable exceeds three, or where
single conductors or multiconductor cables are installed
without maintaining spacing for a continuous length longer
than 600 mm (24 in.) and are not installed in raceways, the
allowable ampacity of each conductor shall be reduced as
shown in Table 310.15(B)(3)(a). Each current-carrying conductor
of a paralleled set of conductors shall be counted as
a current-carrying conductor.

Where conductors of different systems, as provided in
300.3, are installed in a common raceway or cable, the
adjustment factors shown in Table 310.15(B)(3)(a) shall
apply only to the number of power and lighting conductors
(Articles 210, 215, 220, and 230).

It is my opinion that if the heat and cooling are interlocked so that only one or the other can be used at the same time we only have to count the conductors that can run at the same time.

 

[don_resqcapt19]

Looking at the text following Table 310.15(B)(3)(a), it clearly says that all conductors are counted.
I guess under the current code, you would have to use 12 current carrying conductors for derating purposes.

This will be addressed in the 2014 code. The following is the text that follows the derating table as shown in the draft of the 2014 code.

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(B)(5) and (6), and shall not include conductors that are connected to electrical components but that cannot be simultaneously energized. [ROP 6?40]

 

[iwire]

The CMP is not very consistent.


For the 2008 NEC

6-50 Log #1405 NEC-P06 Final Action: Reject
(310.15(B)(2)(a), Exception No. 6 (New))
____________________________________________________________
Submitter: George Stolz, II, Pierce, CO

Recommendation: Add an Exception to read:

Exception No. 6: Of those conductors that are switched cable or raceway
installations, only the maximum number of conductors capable of being
simultaneously energized need to be derated.


Substantiation: In most threeway and fourway switching methods, the load is
alternated between travelers, eliminating the need to include both travelers in
derating.

Panel Meeting Action: Reject

Panel Statement: The proposed exception is not necessary. The present
language of 310.15(B)(2) already permits what the submitter is proposing.

Number Eligible to Vote: 11

Ballot Results: Affirmative: 11
____________________________________________________________

 

[petersonra]

It is simple if there is no interlock. They are all CCC.

If they are interlocked to prevent some of them from not being energized simultaneously, I would entertain an argument about whether they are all simultaneously CCC. It seems to me that the wording is not conclusive on this point.

 

[don_resqcapt19]

The CMP is not very consistent.


For the 2008 NEC

Maybe they changed their mind. New text was inserted below Table 310.15(B)(3)(a) for the 2011 code.

Number of conductors is the total number of conductors in the raceway or cable adjusted in accordance with 310.15(B)(5) and (6).

That says that all conductors in the raceway other than the EGC and grounded conductors that are not current carrying conductors per 310.15(B)(5).
Part of the substantiation for the change is shown below.

This Table was originally added to the Code in 1940 and the column heading remained as ?Number of Conductors? until 1993. During the 1993 NEC revision cycle, the column headings in Table 310.15(B)(2)(a) and Table B.310.11 were editorially changed to ?Number of Current-Carrying Conductors?. There was no Proposal, Comment, or Panel Action to make the change. ...