Current-Carrying ?

[ibew441dc]

(In between two 3-ways , If I run two travelers, a grounded conductor, and an EGC,)

How many current carrying conductors do I have to apply an adjustment factor to?

Originally my brain had me thinking only two current carrying conductors , because only one of the travelers will be carrying current at a time.

But I am not totally confident with my thinking after studying 310.15.

Any thoughts or input?

Ibew441dc

 

[Cavie]

(In between two 3-ways , If I run two travelers, a grounded conductor, and an EGC,)

How many current carrying conductors do I have to apply an adjustment factor to?

Originally my brain had me thinking only two current carrying conductors , because only one of the travelers will be carrying current at a time.

But I am not totally confident with my thinking after studying 310.15.

Any thoughts or input?

Ibew441dc

What are you trying to adjust on a 3way system?

 

[Smart $]

Go with your original thinking. None. You only have 2 ccc's.

The concept behind 310.15 adjustment factors (aka derating) is to protect the wire insulation from thermal degradation. There is no non-faulting condition which generates more than 2 conductors worth of heat in the circuit portion described when compared to 2 conductors wired straight through without the switches... and there are not enough additional wires to hinder the dissipation of the heat generated.

The preceding comments are based solely on my interpretation of the information provided.

 

[360Youth]

(In between two 3-ways , If I run two travelers, a grounded conductor, and an EGC,)

Unless I am missing something you cannot do this anyway because it sounds like you are switching the grounded, which is prohibited.



Edit: Woops, never mind...brain lapse. :roll:

 

[480sparky]

At the far end is the other 3-way. The switch leg goes up to the light, then the grounded supplies the return path. So this install may just have the two travelers and the noodle.

 

[infinity]

Go with your original thinking. None. You only have 2 ccc's.

The concept behind 310.15 adjustment factors (aka derating) is to protect the wire insulation from thermal degradation. There is no non-faulting condition which generates more than 2 conductors worth of heat in the circuit portion described when compared to 2 conductors wired straight through without the switches... and there are not enough additional wires to hinder the dissipation of the heat generated.

The preceding comments are based solely on my interpretation of the information provided.

Although your idea makes perfectly good sense I don't believe that it's supported by the code. Is there an exception that permits you to not count one of the travelers as a CCC?

 

[brantmacga]

Edit: Woops, never mind...brain lapse.

yeh really!!!

 

[ibew441dc]

Is there an exception that permits you to not count one of the travelers as a CCC?

Answer- NO.

That is the very reason my creative mind started ticking.

Ibew441dc

 

[ibew441dc]

(In between two 3-ways , If I run two travelers, a grounded conductor, and an EGC,)

How many current carrying conductors do I have to apply an adjustment factor to?

Originally my brain had me thinking only two current carrying conductors , because only one of the travelers will be carrying current at a time.

But I am not totally confident with my thinking after studying 310.15.

Any thoughts or input?

Ibew441dc

The real motive behind my original post is based on a problem I ran across at work. (try to bare with my description, I wish I had a picture)

Picture a room that is about 175' long and 50'wide, with 3 entrances (one on each long end and one in the middle on one side)

Original design called for 3 circuits(2,4,6) , each with a 3way at end , 4way in middle , and 3way at the other end (simple enough right.)

Originally I ran a 3/4'' EMT between switches( more than adequate to handle 3 sets of travelers, 1 grounded conductor, and 1 EGC. (all are12 awg and total 8 conductors) (no problem so far and derating is no problem)

Now the problem. The owner decided last minute to make it a/b switching for each circuit (and running additional raceway is very difficult task).

For those who can keep up , you can see my problem.
This doubles the number of travelers I need. The conduit is still large enough (less than 40%) , but if I have to consider each of the travelers as a seperate current carrying conductor my wire is not big enough due to the rules in 310.15.

Infinity hits the nail on the head,(there is no exception)

I'm educated enough in electrical theory to sell the inspector on the fact that only 1 conductor will be carrying current at a time (thus totaling the number of CCC to 7), but I take pride in installing code compliant installations.If I am to consider each as seperate ccc there is 13.


What would yo do?

Thanks

Ibew441dc

 

[eric stromberg]

Sounds like it should go on the list for 2011 proposals

 

[mdshunk]

Now the problem. The owner decided last minute to make it a/b switching for each circuit (and running additional raceway is very difficult task)...

What would yo do?

Write up a fat change order and run another pipe to each switching location. It's not a screw-up of yours that you really need to stress about. It's an owner change, for which he needs to pay.

 

[ibew441dc]

Hey Eric,

I know you don't know me , but I have learned a lot from your great participation on Mike Holts video series. Your in the top 10 (in my book) among all who have participated in the 2005 series. Your knowledge and expertise is an asset to our industry.

If someone doesn't beet me to it I think I will propose it for the 2011 NEC.


Thanks

Ibew441dc

edited to correct spelling

 

[ibew441dc]

Write up a fat change order and run another pipe to each switching location. It's not a screw-up of yours that you really need to stress about. It's an owner change, for which he needs to pay.

Thats true , a change order has been issued. ( although throwing a few more conductors in the 3/4'' emt was the easiest way to do it.)

But now there gonna pay.

ibew441dc

 

[eric stromberg]

Hey Eric,

Your knowledge and expertise is an asset to our industry.


edited to correct spelling

Now, if only my head will fit through the front door tomorrow morning...

On the other hand, my wife will probably take care of that

 

[iwire]

Trevor

Although your idea makes perfectly good sense I don't believe that it's supported by the code.

I agree.

Is there an exception that permits you to not count one of the travelers as a CCC?

Answer- NO.

That is the very reason my creative mind started ticking.

I again agree, but actually 'smart' is right according to the CMP.

You only have 2 ccc's.

Sounds like it should go on the list for 2011 proposals

Well it could but our own George already tried for 2008.

The thing is they turned it down, the CMP feels that we can already ignore the dead travelers of 3 and 4 way switches.

6-50 Log #1405 NEC-P06 Final Action: Reject
(310.15(B)(2)(a), Exception No. 6 (New))
____________________________________________________________
Submitter: George Stolz, II, Pierce, CO

Recommendation: Add an Exception to read:

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

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

Panel Meeting Action: Reject

Panel Statement: The proposed exception is not necessary. The present language of 310.15(B)(2) already permits what the submitter is proposing.

Number Eligible to Vote: 11
Ballot Results: Affirmative: 11
____________________________________________________________

 

[infinity]

Bob, thanks for posting the rejected proposal. IMO the wording is not a clear as the CMP thinks that it is.

 

[iwire]

IMO the wording is not a clear as the CMP thinks that it is.

I agree.

It seems that suddenly the CMP wants us to apply common sense to how we read the words.

The code section makes no mention of 'part time current carrying conductors'

 

[infinity]

I agree.

It seems that suddenly the CMP wants us to apply common sense to how we read the words.

The code section makes no mention of 'part time current carrying conductors'

When we have to search through ROP's to prove a point then the NEC is lacking in some verbiage. I understand that not every situation needs to be explained ad nauseam but somethings that are highly unclear should be spelled out directly.