Travelers

[Vegas_sparky]

Here's a hypothetical question. You're derating conductors for multiple 3 way switches in a single conduit. Would you count each traveler as a current carrying conductor, even though only 1 of 2 travelers could ever be energized at any moment in time? Please explain your answer in detail.

 

[ActionDave]

I would count only one traveler as a CCC because only one traveler at at time can carry current. Can't find much more detail to put in.

 

[Sponsor]

 

[Bluebinky]

By that reasoning, if you put the maximum fill of wires and their switches on the same breaker, you would never have to derate them -- only two wires carrying all the current or multiple wires carrying only a fraction of the current each, right?

Said another way -- if they count as current carrying conductors in a box, do they sometimes not count in a conduit?

Actually, I don't really know what I'm talking about, best to ask JW.

 

[ActionDave]

Derating is not about the size of the breaker or the number of breakers that are connected to any of the wires in one pipe. It is all about the number of conductors in that pipe that are carrying current.

Any number of switch legs can carry current, but only one traveler at a time carries current.

 

[Vegas_sparky]

I agree, Dave. I've never not counted them all as CCC, as I've never thought about it until now. I can only imagine trying to explain it to an inspector here. Oh wait, they don't seem to care, unless you've got something that really looks bad.

 

[Bluebinky]

Assuming you can ignore them in conduit, can you ignore the "time multiplexed, non-current carrying travelers" when calculating box fill? I'm not so sure the the inspectors here would buy that...

 

[ActionDave]

That is different. Every conductor in a pipe counts toward fill percentage and box fill.

 

[Jadnashua]

Stuffing the pipe full of conductors means it cannot radiate heat as effectively...current carrying conductors produce the heat - too much of either, and you can have issues.

 

[Bluebinky]

That is different. Every conductor in a pipe counts toward fill percentage and box fill.

Only the current carrying conductors entering/leaving a box all count in box fill. As many EGCs as you want count as one wire. I guess since that is different than all conductors counting inside a conduit counting toward fill may open up the argument...

Since no one seemed to buy the argument that putting all conductors on one breaker would limit the current carrying conductors to an equivalent of two, I believe that the code should be interpreted as saying you need to count all conductors that will normally carry current as carrying their rated currents simultaneously -- that seems to be the intent. To do otherwise (which really does make a lot of sense in the traveler case), probably requires an engineer's sign-off.

It seems you know you've grown up when you cave into the idea that the building codes pretty much frown on creativity.

 

[JWelectric]

Assuming you can ignore them in conduit, can you ignore the "time multiplexed, non-current carrying travelers" when calculating box fill? I'm not so sure the the inspectors here would buy that...

As an inspector, one charged with enforcing the adopted codes, the conductor will count both for raceway and box fill.

 

[Bluebinky]

As an inspector, one charged with enforcing the adopted codes, the conductor will count both for raceway and box fill.

Hey jw, what's your take on the original question?

 

[hj]

quote; f you put the maximum fill of wires and their switches on the same breaker, you would never have to derate them -- only two wires carrying all the current or multiple wires carrying only a fraction of the current each, right?

What does that mean? You can have MANY switches on the same circuit breaker, but that has NOTHING to do the current being carried by any one, or combination, of them. And the only way, "multiple wires carrying a fraction of the current" would apply would be if they were ALL in parallel for the same circuit and device.

 

[Bluebinky]

quote; f you put the maximum fill of wires and their switches on the same breaker, you would never have to derate them -- only two wires carrying all the current or multiple wires carrying only a fraction of the current each, right?

What does that mean? You can have MANY switches on the same circuit breaker, but that has NOTHING to do the current being carried by any one, or combination, of them. And the only way, "multiple wires carrying a fraction of the current" would apply would be if they were ALL in parallel for the same circuit and device.

Connecting wires in parallel is a whole other ballgame -- but you know about that...

If you had two pairs of identical wires each carrying 10A to separate loads, the total resistive losses of the wires would be half of one pair carrying 20A to a single load. Does the NEC allow for that kind of logic to avoid derating wires? Not according to my understanding.

Does the NEC allow half the travelers for 3-way switches to be declared as non-current carrying when inside conduit? My "guess" is no. JW, please do tell, I am curious to hear your answer -- not so I can argue, but rather to learn something from an authority.

 

[ActionDave]

2014 added some language in 310.15 (B)(3) to clarify that travelers don't count. It says something like.... conductors that are connected to components but can't be energized simultaneously don't count.

 

[ActionDave]

If you had two pairs of identical wires each carrying 10A to separate loads, the total resistive losses of the wires would be half of one pair carrying 20A to a single load. Does the NEC allow for that kind of logic to avoid derating wires? Not according to my understanding.
.

No. It is a one size fits all application with some mild exceptions.

 

[hj]

quote; Connecting wires in parallel is a whole other ballgame -

YES, but that is what he is trying to do, so he's playing in THIS ball game.

 

[hj]

quote; Does the NEC allow for that kind of logic to avoid derating wires?

I don't even see the logic. The NEC considers what COULD be connected to the wires, not WHAT it is now Using that "logic" you could have a bunch of 10 watt circuits and fill the conduit as full as possible and not violate the requirement.

 

[Matthew Hermanson]

2014 added some language in 310.15 (B)(3) to clarify that travelers don't count. It says something like.... conductors that are connected to components but can't be energized simultaneously don't count.

I sure don't see that. The direction towards 300.3 has nothing to do with travelers.

I agree that the pair of travelers should be counted as one current carrying conductor.
But I can't lay my hands on a section of code to back me up.

 

[Matthew Hermanson]

Found It!
It is on the note at the bottom of TABLE 310.15(B)(3)(a)

 

[ActionDave]

Found It!
It is on the note at the bottom of TABLE 310.15(B)(3)(a)

Sometimes looking through the NEC is like an Easter egg hunt.