Travellers & Derating

[George Stolz]

1.) NEC Section/Paragraph: 310.15(B)(2)(a)
2.) Proposal Recommends: new text
3.) Proposal: Add exception:

Exception No. x: A conductor in three-way and four-way switch loops in cable or raceway installations shall be omitted from adjustment factors where the load connected cannot be connected to another supplying conductor at the same time.


4.) Substantiation: In most threeway and fourway switching methods, the load is alternated between travellers, eliminating the need to include both travellers in derating.

Is the term "traveller" defined or used anywhere else in the NEC? If I could use that term, it would shorten that exception a bunch...

[ March 20, 2005, 08:28 AM: Message edited by: georgestolz ]

 

[charlie]

Re: Travellers & Derating

Not that I know of. You can use the term in the substantiation but not in Code text unless you offered a definition to be placed in 310.2. This would require renumbering the existing 310.2 which you would need to state in your proposal (you don't need to indicate how the renumbering is to be done, the CMP will take care of that part).

Your reference will need to be 310.15(B)(2)(a) Exception No. 6 and to indicate that in the text. If the CMP wants to change it, they can.

Overall, this is a good proposal. I think it will fly.

 

[George Stolz]

Re: Travellers & Derating

Do you think it would add clarity to add a "traveller" definition? Try to see it with fresh eyes.

Exception No. 6: A traveller in cable or raceway installations shall be omitted from adjustment factors where the load connected cannot be connected to another traveller at the same time.

Travellers: A set of conductors installed in three-way and four-way switch loops to alternate the supply of a load, to allow the load to be energized and de-energized from different switches.

There's got to be a shorter way of saying that and have it still be legal.

How do you submit two (definition & exception) proposals at the same time?

[ March 20, 2005, 09:40 AM: Message edited by: georgestolz ]

 

[George Stolz]

Re: Travellers & Derating

As I sit and ponder, I think the traveller definition is best left out. More trouble than it's worth. I can't think of another occasion to use it, other than maybe 200.7 to put restrictions on how to wire a threeway (which I don't want to do). 404 has gotten by just fine without it.

I have just as much text one way as the other. I think the original is the stronger idea. I think.

 

[jwelectric]

Re: Travellers & Derating

see 200.7 (C) (2)

 

[al hildenbrand]

Re: Travellers & Derating

George,

Maybe opening up the wording a little bit, . . .Travellers can be used in some goofy ways (I'm thinking of all the variations that use a traveller to carry the unswitched hot between two switches for the extension of the branch circuit past the "far" switch.)

It occurs to me, also, that a transfer switch, or any single pole - multiple throw switch that uses the conductors connected to it non-concurrently are going to fall under this idea when the switched conductors are in the same raceway or cable.

This is really about the heat generated by the I?R of the conductors that are operating at any one time. So, yeah, I agree with your later thought about not using the direct reference to travellers (and the definition that requires). Travellers alone are not enough. So: something like: Of those conductors that are switched, only the maximum conductors capable of being simultaneously energized need to be derated.

It also occurs to me that multiwire circuits, switched with multipole - multiposition swithes will have an additional deduction when the loads supplied are not nonlinear.

 

[George Stolz]

Re: Travellers & Derating

Exception No. 6: Of those conductors that are switched in cable or raceway installations, only the maximum number of conductors capable of being simultaneously energized need to be derated.

That's tight. I like it. I wonder if other eyes see holes in it?

 

[physis]

Re: Travellers & Derating

Where two or more conductors in a cable or raceway are prevented from simultaneously carrying current by the inherent operation of a device or controller those conductors shall be permitted to be counted as one current carrying conductor.

[ March 25, 2005, 01:09 AM: Message edited by: physis ]

 

[charlie]

Re: Travellers & Derating

Sam, It won't work if you say two or more can be counted as one.

 

[George Stolz]

Re: Travellers & Derating

Exception No. 6: Of those conductors that are switched in cable or raceway installations, only the maximum number of conductors capable of simultaneously carrying a load need to be derated.

Changed energized to carrying load. In transfer switches the other conductors can be energized, but not carrying load.

Look out! Sam's got a proposal pencil!

Editted spelling.

[ March 25, 2005, 08:11 AM: Message edited by: georgestolz ]

 

[charlie]

Re: Travellers & Derating

George, it is not that early, you are just in the wrong time zone.

 

[physis]

Re: Travellers & Derating

That's funny because the or more is what I edited in after I started thinking that George might be after including more than just 3 and 4 way travellers.

I don't see where it doesn't work. Those conductors that are prevented from operating simultaneously are counted as one. The logic is impeccable. I think.

 

[George Stolz]

Re: Travellers & Derating

Originally posted by physis:

Where two or more conductors in a cable or raceway are prevented from simultaneously carrying current by the inherent operation of a device or controller those conductors shall be permitted to be counted as one current carrying conductor.

Okay, done with work--a pot of coffee and two Pepsi's down. I think I see the problem.

Where a set of two or more conductors in a cable or raceway are prevented from simultaneously carrying current by the inherent operation of a device or controller, each set shall be permitted to be counted as one current carrying conductor.

If two sets of threeways are in the same raceway, the original wording would have allowed both sets of travellers to be considered one conductor. Is that what you were thinking, Charlie?

 

[physis]

Re: Travellers & Derating

I considered that and still decided that the language handles it. But at the same time I have no problem with the additional clarity. The less thinking necessary to understand it the better.

 

[physis]

Re: Travellers & Derating

Where a set of two or more conductors in a cable or raceway are prevented from simultaneously carrying current by the inherent operation of a device or controller, each such set of conductors shall be permitted to be counted as one current carrying conductor.

Edit: My last edit disappeared when I opened the editor. That's been happening a lot.

[ March 25, 2005, 06:56 PM: Message edited by: physis ]

 

[physis]

Re: Travellers & Derating

Shoud it be [device(s)] or [controller(s)]?

 

[George Stolz]

Re: Travellers & Derating

I'd say device.

 

[mc5w]

Re: Travellers & Derating

I would say switch, relay, or controller. This would also cover multiple speed motors.

I would also place a limit of 5 conductors on the group of conductors that can be counted as 1 conductor. The conductors that are not carrying current still tend to block flow of heat.

Also, I would put in a stipulation that the cable or raceway cannot be embedded in thermal or soundproffing insulation.

 

[George Stolz]

Re: Travellers & Derating

Would there be a practical reason to run more than 5 conductors in parallel? I haven't had the pleasure of doing the type of work you're describing, so I'm at a loss.

I don't agree with adding the insulation part, as the temperature corrections are not taking place in 300.4, so why diverge from the theme?

 

[physis]

Re: Travellers & Derating

By the Georginator:

If two sets of threeways are in the same raceway, the original wording would have allowed both sets of travellers to be considered one conductor. Is that what you were thinking, Charlie?

If two sets of traveller are in a raceway.

Both lights are on.

Two of the four travellers are carrying current.

They are not prevented from symultaneously carrying cyrrent. So they are not counted as one conducter.

The logic already disallows misapplying it. But I still have no problem with extra clarity.

Just so ya know.