Is a switchleg counted as a current carrying conductor

[Jason Spray]

Trying to calculate the de-rating factor for conduit fill, Is the switch-leg counted as a current carrying conductor when it is run with the hot? I'm sure I'm getting confused with neutral not having to be counted, or box fill calculations and multiple grounds counting only once. Sorry for the silly question, sometimes my old mind gets lost.

 

[LarryFine]

Is the switch-leg counted as a current carrying conductor when it is run with the hot?

Yes.

 

[infinity]

Yes it does count but IMO there are instances where it shouldn't.

 

[jap]

Yes it does count but IMO there are instances where it shouldn't.

Like when the switch is shut off ????


Jap.

 

[LarryFine]

How about a pair of travelers, when only one can be energized at a time?

 

[jap]

Couldn't all conductors be considered current carrying at one time or another?

JAP>

 

[retirede]

Couldn't all conductors be considered current carrying at one time or another?

JAP>

But not simultaneously- ex. 3 way.
At least as far as derating is concerned.

 

[jap]

But not simultaneously- ex. 3 way.
At least as far as derating is concerned.

If the 3 way switches were taken out, and the travelers tied together to make the load work, would the heat produced in the multiple conductors be more than if only one of the travelers were used in the 3 way situation ?

JAP>

 

[LarryFine]

If the 3 way switches were taken out, and the travelers tied together to make the load work, would the heat produced in the multiple conductors be more than if only one of the travelers were used in the 3 way situation ?

Ignoring the fact that you can't parallel small conductors for a moment, you're assigning half of the current to each wire. Seems that each wire emits half the heat, and there are two of them. That works out to be a wash. Plus, you now have one more CCC to consider.

 

[jap]

Ignoring the fact that you can't parallel small conductors for a moment, you're assigning half of the current to each wire. Seems that each wire emits half the heat, and there are two of them. That works out to be a wash. Plus, you now have one more CCC to consider.

I agree.

So with that being said, the de-rating issue shouldn't even come into play even if all the conductors were energized simultaneously.

JAP>

 

[wwhitney]

you're assigning half of the current to each wire. Seems that each wire emits half the heat, and there are two of them.

As power is I²R, each wire emits 1/4 the heat, so the total heat is halved.

Cheers, Wayne

 

[jap]

As power is I²R, each wire emits 1/4 the heat, so the total heat is halved.

Cheers, Wayne

Well when you put it that way it seems we ought to allow paralleling of smaller conductors, stuff the pipes full, and do away with having to de-rate all together.



JAP>

 

[kwired]

Ignoring the fact that you can't parallel small conductors for a moment, you're assigning half of the current to each wire. Seems that each wire emits half the heat, and there are two of them. That works out to be a wash. Plus, you now have one more CCC to consider.

I agree.

So with that being said, the de-rating issue shouldn't even come into play even if all the conductors were energized simultaneously.

JAP>

If you have other circuits in same raceway, your total current carrying conductor count still goes up and therefore your adjustment factor may change. The "travelers" would only be carrying half the current they otherwise would carry if there were a single conductor - they won't need to increase in size because of a different adjustment factor, as they are carrying less to begin with. Those other circuits in the same raceway may require increased conductor sizes though.

Remember for fixed lighting and a 15 amp branch circuit - you don't have to be able to carry 15 amps on the conductor - you only need to carry the actual connected load. General use 15 amp receptacle circuit you need to figure you might be loaded to 15 amps and have to make adjustments based on 15 amp load.

More direct response to OP - three way "travelers" only carry current on one of them at a time, you only need to count one conductor as current carrying for ampacity adjustment reasons. Simple two wire "switch loop"- both conductors carry same current at same time. Throw in a neutral as is now required for most lighting applications - technically that neutral is a current carrying conductor if not arranged to carry unbalanced current. If you only have one phase involved in the "switch loop", then the neutral is definitely a current carrying conductor - though it typically will only be carrying load in the mA ranges at most.:blink: