traveling bus three way

Status
Not open for further replies.
C

CAsparky

Member
Location
San Diego
Im doing a room addition. The homeowner asked my to look at a three way in which he had replaced the old light it controlled. Upon replacing he noticed signs of excessive heat. There was black rings on the ceiling and he said the insulation on the wires appeared slightly charred. I inspected the light and saw the rings but it was hard to tell which wire was heating up because the old insulation was stripped back a little more and he had taped them.
The house was built in the 40's and they used steel flex. All conductors on the three ways were blue and each common had a knot in the wire. After doing a search here I found the traveling bus three way thread which really helped me figure out that is the method they used.
I read in the Traveling bus thread that this is a legal method. Anybody have any input if this method could have caused the heat in the fixture. Or do you think it could have been a bad connection or something with the old fixture. Thanks for any replies.
 
CAsparky said:
I read in the Traveling bus thread that this is a legal method.
Click to expand...
Technically, if we overlook the grammatical error in 310.4 and interpret it as it is meant, then the Travelling Bus is illegal. When both switches are in the common-to-hot position (the light would be off) then loads downstream of the Travelling Bus would be fed from two conductors in parallel.

Therefore, since the conductors are not 1/0 or larger, we have a 310.4 violation. (310.4 is misworded, as I mentioned - but convince an inspector (or the Code-Making-Panel) of this and I'll mail you a quarter. We can delve into why it's misworded, if you ask. :D )

Anybody have any input if this method could have caused the heat in the fixture.
Click to expand...
It's not possible, if all the ungrounded conductors are supplied from the same breaker. Conductors in parallel of uneven length will carry different amounts of current; but if they're supplied from the same breaker the overall current on each conductor of the pair would be less than a single conductor before or after the Bus on the circuit.

I'd say Dennis is on the right track. :cool:
 
"Traveling Bus"???? Is this the AKA 'Hollywood', 'Chicago' and of numerous other monikers illegal 3-way?

The charring can be a varity of things. Over lamping, or often just a loosely screwed in bulb arcing. And in your case, as roughly 50% of the time - the shell of the lamp base is hot, and I have noticed that this does something odd - it seems to generate more heat at the lamp base - induction maybe. Just something I have noticed....
 
Does anyone have a schematic for this type of switching arrangement? Not that I ever plan to use it, but when I see it in the field it would be helpful to recognize what's going on. (or not going on:grin: )
 
TommyC said:
Does anyone have a schematic for this type of switching arrangement?
Click to expand...

Check out ElectricPuzzles

In particular, check out the link at the bottom, the solution to puzzle number two. It uses a switch to parallel a circuit conductor, which I believe is a NEC violation, but even if it isn't, I believe it's just not good electrical engineering practice. I wrote the guy on it, he thinks it's fine. Be interested what the code experts think :)
 
Status
Not open for further replies.
Top