The travelers should each be counted as a current carrying conductor, but remember, if this is a 15 or 20A circuit, derating will not affect wire size/circuit breaker choice until you exceed 9 current carrying conductors.

Thank you, Norm. Groan, that's pretty much what I suspected the answer to be.

In this case, it's a mix of 15- and 20-amp circuits and the plan is right on the bubble. That is, if two travellers count as one, then I have 8 total. Otherwise, I have 10.

Common sense suggests that it's a stupid reason to pull #10s instead of 12s and 12s instead of 14s when two of the conductors are guaranteed to be dead at any given time.

But, oh well, code is code whether it always makes sense in context or not.

I would count them as 1 same as when using a multiwire branch circuit the neutral doesn't count.
Don't confuse derating with conduit fill. Those are two different calculations.

For fill, two conductors.

For derating, a single conductor since they cannot both be active at the same time.

This is exactly analogous to a multi-wire branch circuit.

3-wires for fill, two for derating.

Remember you get to start with the actual conductor ampacity for derating (not the footnote limit of 15 A on #14 and 20 A on #12).

joed wrote: "I would count them as 1 same as when using a multiwire branch circuit the neutral doesn't count."

Now there's an answer I like better. :-) Thanks.

and brick':

"For fill, two conductors.

For derating, a single conductor since they cannot both be active at the same time.

This is exactly analogous to a multi-wire branch circuit.

3-wires for fill, two for derating."

Makes sense to me. Thanks.

Remember you get to start with the actual conductor ampacity for derating (not the footnote limit of 15 A on #14 and 20 A on #12).

Yup, capisce. Of course now that I'll only have eight, I'm home free anyway.