Why was 1/0 chosen as min parallel size

[LarryFine]

Re: Why was 1/0 chosen as min parallel size

Originally posted by georgestolz:
One thing that has kinda had me scratching my head in the past is, what about circuits where you loop around the room, and have multiple threeways, and everything is on the same circuit so the neutrals are tied together.

(I know that's got to be the most terrible description ever, but I'm hoping folks know what I'm getting at.

Is this a parallel path for the neutrals, when say, two threeways start at the same box, end at the same box, and all the neutrals are tied together at the switchleg side of the system? the white conductors of each set of 14/3 cable are in parallel. So this is technically illegal. Has anyone seen a problem with this?

George, I never recombine neutrals once separated, like we would with EGC's. If I'm running two or three 3-way switch runs together, I'll either keep the neutrals separate once they leave the first (fed) box, or use one neutral (as long as it's the same circuit, of course!)

Let's say we have two 3-way switch runs across a large room, same cicruit. If there are only the two 3-ways in the far (legs-out) box, I'll run a 14-3 and a 14-2, and recolor the white in the 14-2; this cable is now just travelers; the white in the 14-3 is the neutral for both fixture groups.

If the far box also has another switch(es), needing a hot, I'll run three 14-2's, using one cable as hot and neutral and the other two cables (again, with recolored whites (different colors)) as travelers. Note that these methods avoid redundant conductors, which helps keep box-fill down.

[Edited 'cause my fingers ignore my brain]

[ July 21, 2005, 05:23 PM: Message edited by: LarryFine ]

 

[LarryFine]

Re: Why was 1/0 chosen as min parallel size

[Deleted for the same reason :roll: ]

[ July 21, 2005, 05:25 PM: Message edited by: LarryFine ]

 

[iwire]

Re: Why was 1/0 chosen as min parallel size

George code wise it's a 310.4 violation.

 

[George Stolz]

Re: Why was 1/0 chosen as min parallel size

Originally posted by jwelectric:
When someone calls me about an Arc fault that won?t hold this is one of the first thoughts that goes through my mind.

Why would this configuration kick an arc fault? Everything would be back in line by the time it gets back to the breaker...?

I guess I'll start separating them all. To be honest, I'd never been trained that way, and never given it much thought, and never had a problem with it.

Bob, I sense a certain amount of restraint in your post. Is there a "but" you'd like to share?

 

[iwire]

Re: Why was 1/0 chosen as min parallel size

Originally posted by georgestolz:
Why would this configuration kick an arc fault? Everything would be back in line by the time it gets back to the breaker...?

If your joining grounded conductors of different circuits only some (or more) current will get back to the AFCI breaker. This will trip the GFCI part of the AFCI.

Originally posted by georgestolz:
Bob, I sense a certain amount of restraint in your post. Is there a "but" you'd like to share?

Everyone seemed to be jumping on you, I did not want to join on the band wagon.

You strike me as a guy that wants to do the right thing, not someone trying to find shortcuts.

 

[LarryFine]

Re: Why was 1/0 chosen as min parallel size

Originally posted by georgestolz:

Originally posted by jwelectric:
When someone calls me about an Arc fault that won?t hold this is one of the first thoughts that goes through my mind.

Why would this configuration kick an arc fault? Everything would be back in line by the time it gets back to the breaker...?

http://www.mikeholt.com/codeforum/ultimatebb.php?ubb=get_topic;f=11;t=007524

 

[George Stolz]

Re: Why was 1/0 chosen as min parallel size

Originally posted by iwire:
If your joining grounded conductors of different circuits only some (or more) current will get back to the AFCI breaker. This will trip the GFCI part of the AFCI.

No, from the same circuit. Perhaps that's what Mike was thinking too.

Neutrals separated and rejoined from the same circuit shouldn't kick an AFCI.

I'm not looking for a shortcut, I was just curious of the feel of the room. In my upbringing, this incidental parallel path is not regarded as being a hazard. Now that I'm #12 in the company (

 

[iwire]

Re: Why was 1/0 chosen as min parallel size

Originally posted by georgestolz:
Neutrals separated and rejoined from the same circuit shouldn't kick an AFCI.

I agree with that.

I am fairly certain Mike was thinking about mixed circuits just as I was.

Originally posted by georgestolz:
In my upbringing, this incidental parallel path is not regarded as being a hazard.

Putting aside possible EMF issues I agree with you it is not a hazard but it is a violation of 310.4.

 

[hurk27]

Re: Why was 1/0 chosen as min parallel size

Thanks Don

I did some reading HERE
It sounds like The magnetic fields surrounding each cable are much harder to control in smaller conductors and can cause un-balanced current in them even when they are equal in length. Your right that the actual conductor resistance doesn't play a big part in this as the spacing of the conductors will have a much more effect upon each conductor. If you click on the above "HERE" link then the continue(2 more pages) at the bottom it gets more into this effect and even explains how the same effect works in motors.
So you could have the same length conductors and have one over loaded

 

[Mega VAR]

Re: Why was 1/0 chosen as min parallel size

Why do you want to parrallel conductors smaller than 1/0?
250.122(F) Conductors in parallel. Where conductors are run in parallel in multiple raceways or cables as permitted in 310.4, the equipment grounding conductors, where used, shall be run in parrallel in each raceway or cable. One of the methods in 250.122(F)(1) or (F)(2) shall be used to ensure the equipment grounding conductors are protected.

If you absolutely wanted to run parallel grouned conductors under 1/0,

250.122 (F)(2) Ground-Fault Protection of Equipment Installed. Where ground-fault protection of equipment is installed, each parallel equipment grounding conductor in a multi-conductor cable shall be permitted to be sized in accordance with Table 250.122 on the basis of the trip rating of the ground-fault protection where the following conditions are met:.....