Are ten wires always derated @ 50%?

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jason sleeth

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A unique situation was brought to my attention. There was a pipe with ten wires in it and two of the wires were travelers for a three way. Since the wires were travelers only one of them would be a current carrying conductor depending on which way the switch was. How does the code address the situation. If only 9 wires are condidered current carrying conductors you would only have to derate the wires to 70% of the ampacity. If all wires have to be considered then you have to derate the wires @ 50%. What is the call?
 
Re: Are ten wires always derated @ 50%?

Pierre,
It doesn't say it exactly, but only one of the travelers can be carrying current any given time. There are no conditions where both would be carrying current under normal operating conditions. The rule says we only have to count the current carrying conductors so, I would only count one of them.
Don
 
Re: Are ten wires always derated @ 50%?

I agree don, common sense prevails, only 9 CCC. NEC is not an instruction or training manual.
 
Re: Are ten wires always derated @ 50%?

The other 8 conductors may go to recpts. that never will get used,you still have to count them.

What if there were 3 or 4 three ways in that conduit? they still take up space that was figured for cooling.
 
Re: Are ten wires always derated @ 50%?

As Frank has mentioned, there could be other conductors in the raceway that may not even be used, such as to receptacles or even to lighting fixtures that are seldom if ever used. Yet those conductors are taking space and keep the other conductors from being able to dissipate heat. I still think that the travelers are to be counted, otherwise the NEC would have an exception for them.


"NEC is not an instruction or training manual."

I am not sure how this pertains to this thread?
 
Re: Are ten wires always derated @ 50%?

"FPN: The temperature rating of a conductor(see
310.13 and Table 310.61) is the maximum temperature, at any location along its length, that the conductor can withstand over a prolonged time period without serious degradation. The allowable ampacity tables, the ampacity tables of Article 310 and the ampacity tables of Annex B, the correction factors at the bottom of these tables, and the notes to the tables provide guidance for coordinating conductor sizes, types, allowable ampacities, ampacities, ambient temperatures, and number of associated conductors. The principal determinants of operating temperature
are as follows:
(1) Ambient temperature ? ambient temperature may vary along the conductor length as well as from time to time.
(2) Heat generated internally in the conductor as the result of load current flow, including fundamental and harmonic currents.
(3) The rate at which generated heat dissipates into theambient medium. Thermal insulation that covers or surrounds
conductors affects the rate of heat dissipation.
(4) Adjacent load-carrying conductors ? adjacent conductors have the dual effect of raising the ambient temperature and impeding heat dissipation.

[ September 10, 2005, 06:32 AM: Message edited by: pierre ]
 
Re: Are ten wires always derated @ 50%?

Originally posted by pierre:
Yet those conductors are taking space and keep the other conductors from being able to dissipate heat. I still think that the travelers are to be counted, otherwise the NEC would have an exception for them.
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I disagree, if the non-current carrying conductors make a difference the NEC could do away with all the rules of what is and what is not a current carrying conductors.

Instead we would derate based on the total number of conductors including Grounding and Grounded conductors at all times.
 
Re: Are ten wires always derated @ 50%?

Originally posted by pierre:
Bob

My intention is not to count noncurrent carrying concuctors, just current carrying. Travelers are current carrying conductors - yes? Technically
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Technically the neutral of a multiwire branch circuit will very likely carry some current at all times. But even though it will carry current and it takes up space the NEC allows us not to count it.

Technically the EGC may carry a 'boat load' of current at some point. Still even though it takes up space and may carry current we do not count it.

My point is the NEC as rule does not count conductors for derating just because they take up space in the raceway.

IMO in the case of the three way it is imposable by design for both travelers to carry current at the same moment, therefore the two travelers count as one current carrying conductor.

Often I run two 2" raceways out of a 42 circuit panel.

In each raceway will be,

21 ungrounded conductors

7 grounded conductors

1 grounding conductor

The total conductor count is 29, as far as the NEC is concerned for derating purposes it is 21 conductors, the eight 'extra' conductors do not effect the derating rules just because they take up 'space' in the pipe.

All that aside I agree it is a murky area of the code, each AHJ and electrician will see it differently. :)

[ September 10, 2005, 08:26 AM: Message edited by: iwire ]
 
Re: Are ten wires always derated @ 50%?

My point is the NEC as rule does not count conductors for derating just because they take up space in the raceway.
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I'm with you Bob. Derating applies to current carrying conductors within the raceway. It does not apply to neutrals under certain conditions, EGC's or even spare conductors pulled in a conduit for future use. And since traveler conductors from a 3-way switch can only carry current one at a time I would count them as only one CCC. After all only one will carry current when the light is on.
 
Re: Are ten wires always derated @ 50%?

I love to stir the pot!!!! :D It helps one to think a little further, and usually gets a lot of responses to make one think differently than before.


"7 grounded conductors

1 grounding conductor

The total conductor count is 29, as far as the NEC is concerned for derating purposes it is 21 conductors, the eight 'extra' conductors do not effect the derating rules just because they take up 'space' in the pipe.

All that aside I agree it is a murky area of the code, each AHJ and electrician will see it differently. "


These 8 conductors (types) are specifically addressed in Art 310.15 (B)(2).

Travelers are not :confused:

I just want people to think about this.

How many times have we mentioned that we need to go by what is written, not intent?
 
Re: Are ten wires always derated @ 50%?

Pierre,
I still think that the travelers are to be counted, otherwise the NEC would have an exception for them.
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Then why are EGCs not counted? The chances of both travelers carrying current at the same time is about the same as the EGC carrying current.
Don
 
Re: Are ten wires always derated @ 50%?

Hello Don

I am not specifically in favor of counting travelers (even though I mentioned it), what I am trying to do is make sense of what is actually written - by "stirring the post"

I know you know what is written. Why did they leave travelers out of the exceptions? Was that intentional or an oversight, or something that is to be taken for granted?
 
Re: Are ten wires always derated @ 50%?

How about another stir: What about the new "smart" dimmers that no longer use the conventional threeway switching method, and use the red "traveller" as a communicator instead? Is it a CCC? :D
 
Re: Are ten wires always derated @ 50%?

Originally posted by pierre:
How many times have we mentioned that we need to go by what is written, not intent?
Click to expand...
I know I have 'mentioned' that at least once or twice. :D

What I see is the number of current carrying conductors is what Table 310.15(B)(2)(a) is based on.

Conductors like spares, EGCs or travelers that do not carry current are not IMO current carrying conductors.

Lets stir some more. :D

I run two 3 phase 3 wire 100 amp feeders up to roof units from the service. I use one 2" raceway that contains six - 3 AWG ungrounded conductors and one 8 AWG EGC.

A violation right?

Well how about if one of these feeders runs a heating unit and one feeder runs a cooling unit.

Theses two separate units are interlocked so only one unit may run at a time.

Now do I have 3 or 6 current carrying conductors in this raceway?

[ September 10, 2005, 10:11 AM: Message edited by: iwire ]
 
Re: Are ten wires always derated @ 50%?

Hello Pierre, there would not be a reason to have an exception for travelers when only one of any set could be current carrying at any given instant.

In otherwords, the unused traveler(s) doesn't exist at the times it isn't (or they aren't) carrying current.

Roger
 
Re: Are ten wires always derated @ 50%?

What about the new "smart" dimmers that no longer use the conventional threeway switching method, and use the red "traveller" as a communicator instead? Is it a CCC?
Click to expand...
I don't think that conductor is counted because it is not a power or lighting conductor. See Ex #1 to 310.15(B)(2).
Don
 
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