travellers

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buck33k

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Travellers in a three way circuit occupy a conduit along with other conductors.

Are both travellers counted as current carrying conductors for purposes of derating?

I seem to remember a discussion of this before but cannot find it in the archives.

Buck
 
Re: travellers

I'd guess technically they are counted, as there is no exception in 310.15 for that. There should be, and an AHJ would probably agree, but technically, I'd say it should be counted. IMO.
 
Re: travellers

Here is a past discussion on the topic.
Miss ya' Bennie.

Edit per Geo's request. Thanx George, I didn't check it.

[ March 17, 2005, 12:24 AM: Message edited by: luke warmwater ]
 
Re: travellers

Well, I think that George should put a proposal together.

Al makes a good if not iffy argument in the other thread. I don't think it would amount to anything more than giggle material in Colorado though.

It's pretty obvious that there's no need to count both travellers. I'm gonna go renegade on this one and say "for the sake of reason I'll decide for the AHJ".

It's the same concept as the heater/AC in Article 220.

Oh man, you're right Bob. There is the lawyer/liability thing. I guess common sense and good judgement can't just be allowed to run amok anymore.
 
Re: travellers

I read the older thread and this thread.

The NEC says to count it.

Look at it this way, since this is dealing with heat. If there were a total of 9 current carrying wires, 2 of them are travlers, so there would be 8 current carrying wires (heat would equal 8 x Xdegrees). When it is switched, there would still be 8 current carrying wires plus the residual heat from the switched conductor (heat would equal 9 x Xdegrees).

Yes, I know this is extreme and the heat would disipate quickly, however, it is just one way to look at it.
 
Re: travellers

Uh, one problem with that.

If two wires (common and traveller) are carrying current (i.e. the light is on), when the switch is flipped the light turns off, so they would be carrying no current. All three would cool down. :D

Current carrying, not voltage carrying. :D
 
Re: travellers

Rich000,

When the current on one traveller stops, leaving that conductor warm, that conductor starts to cool. No new calories of heat are released from the I?R electric to thermal energy conversion in this conductor after the current stops.

The other traveller starts conducting, and it is cool, having only the heat in it that it has absorbed from the ambient of its immediate vicinity. As the I?R electric to thermal energy conversion occurs, calories are added to the conductor and its temp starts to rise.

The units of heat, calories (or BTUs), collect, raising temperature, and flow outwards to volumes of lower concentrations of heat (lower temperature) at a rate determined by the temperature difference and the thermal conductivity of the materials (along with radiation and convection).

Bottom line, when only one traveller at a time is carrying current, the calories released from the I?R is constant whether the current stays in one traveller all the time, or goes back and forth. The thermal stress on the conductors in a raceway will not increase from the stress created by one conductor.
 
Re: travellers

Basically the premis suggests that you can get free energy. Neat idea but we'd be using that scheme to build heaters if it were true.
 
Re: travellers

Psst! I'll sell you a threeway switch that'll heat your house. ;)
 
Re: travellers

This is similar to the argument for putting the 220V A/C and the 220V baseboard heat on the same breaker because you are running out of space in the panel.

I once had an inspector fail me because I used an extension ring on a j-box in new installation. 'Workmanship like manner' because I didn't plan accordingly.
If you need this one conductor that bad, this must be an extreme need.

If all else fails, you can always use the neutral as a traveller and have your very own Farmer 3way.
 
Re: travellers

So, Steve,

Are you saying we should use the Code to know where to overbuild? And if so, how do we determine how much to overbuild? Is it in the Code?
 
Re: travellers

I didn't say we should over build. Hey, I was mad at that Inspector for years.
I do see his point, though. We as installers should always consider that workmanlike manner (110.12). Is it appropriate to try and fudge on the code? Not really. We have all done it though. Should we be trying to rationalize and justify the NEC to adapt to our installation methods or should we adapt to the NEC. Most everyone would agree with the latter (until an instance like this comes up).
I understand Buck's dilemma.
I would rather look at the reason why we are rationalizing the NEC.
If the reasons are because (a) we are lazy, or (b) we forgot something, then the rationalization would be wrong.
IF the reasons are because this is the ONLY way to reasonably accomplish something, then MAYBE you could justify you rational.
As far as overbuilding, we should look at 90.8 Wire Planning (A) Future expansion and convenience when planning all of our installations.
 
Re: travellers

I don't disagree that trying to side step the code is a dishonorable practice.

However in this case you're more likely to find current on the EGC than you are on the unused traveller. The EGC is not counted as current carrying.

Although some might say it's close, the code isn't quite perfect.

This one, in my opinion, falls outside of an obvious pattern. But I agree that as far as interpreting code both travellers have to be counted and should be to be compliant.

But it's a worthy debate.
 
Re: travellers

In order to implement 90.8, we have to know where to start from. I don't think this is academic. When I talk to my customer about what they have to have, by the minimum requirements of the NEC, I establish the benchmark from which my customer can purchase 90.8 future expansion and convenience.

But, this break from 70% to 50% derating is an interesting one, in my opinion, and not much related to 90.8.

Consider:

A raceway with four sets of travellers, a hot and a neutral. That is a total of ten conductors.

My raceway is 1", so there is lots of room for the future.

Do I have six, or ten, current carrying conductors?
 
Re: travellers

Thank you JW, but there are far wiser people out here than me.

I'm on Al's side with the idea of how important or unimportant the interpretation of a code is. It might seem like something can easily be done to make an interpretation a moot point. But, like in Al's example, it can end up making a real big difference.

And taking a close look at stuff like this make our code knowledge that much better.


Basically, although it might seem petty, there's no down side. :)

[ March 17, 2005, 05:13 PM: Message edited by: physis ]
 
Re: travellers

If Buck wants to add a 3way to an existing remote building or garage, and the existing run out there is 200' of 1/2" RIGID, and whether or not he can do it is based on this rule, I can see his point. Believe me, I've been there.

However, if you are planning your pipe run across a conference room with multiple switches and loads with the 3ways to go with them, THEN you should be planning ahead and sizing that pipe appropriately. This is where I refer to 90.8(A). And that would mean counting ALL conductors. Whether they are intermittent or not, they all carry current.
The only conductors that don't (in respect to this code rule) are Equipment Grounding Conductors.

I know it sounds petty, but whether they are intermittent or non-coincidental, all 10 of those conductors in that 1" raceway do carry the circuit current.
 
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