Multiwire Branch Circuit Tap

[jimells]

Does the NEC prohibit splitting a multiwire branch circuit into 2 separate cables, one for phase A and one for phase B? I've been searching the forum and the code book and can't find a specific reference to this.

Someone previously ran 12-3 NM to the 2nd floor and apparently only used the black and white conductors. (I say "apparently" because the cable terminates at a hidden splice- I suspect K & T ).

I plan to find the splice, replace the K & T, then use the red conductor to add a new circuit for the 2nd floor.

Art. 240.20(B)(1) says I only need individual single-pole OCPDs with handle ties but a two-pole CB makes a lot more sense to me. And 240.2 tells me these aren't really "tap conductors" if I continue the circuits with 12 AWG, so 240.21 doesn't apply.

My conclusion is that this is permitted. Do you all agree?

 

[hurk27]

Re: Multiwire Branch Circuit Tap

Art. 240.20(B)(1) says I only need individual single-pole OCPDs with handle ties but a two-pole CB makes a lot more sense to me.

That's not what it's saying. Look again it says:

with or without approved handle ties

And the only time a multi-wire circuit has to have handle ties is when both phases land on the same yoke.(or device) Look at 210.7(C)

But watch out for the Chicago three-way as many old houses used a three conductor to feed power up to the second floor and used the red conductor for one of the contacts on the light the common from the other three-way would go to the other contact on the light. then hot and neutral would be the travlers.
Just a thought?

 

[steve66]

Re: Multiwire Branch Circuit Tap

Does the NEC prohibit splitting a multiwire branch circuit into 2 separate cables, one for phase A and one for phase B?

I can't think of any article that deals with this. My opinion is that it is probably OK to do that.

Steve

 

[ryan_618]

Re: Multiwire Branch Circuit Tap

Originally posted by hurk27:

...And the only time a multi-wire circuit has to have handle ties is when both phases land on the same yoke.(or device) Look at 210.7(C)

Hi Wayne. I would disagree with oyur statement above. 210.4(B) addresses this for dwelling units, but 210.7(C) is a different animal. 210.7 is for multiple]/i] branch circuits, not multiwire branch circuits. Multiple branch circuits would be a black with a white and a red with a white. Remember that 210.4(A) states that "a multiwire branch circuit shall be permitted as multiple branch circuits". If that is true, than the contrary is true as well, that a multiwire branch circuit may be considered one circuit as well. I don't think the rule of 210.7 applies here, if it did, it would be found in 210.4 and 210.4(B) would be deleted becasue it would then pertain to all occupancies.

 

[jimells]

Re: Multiwire Branch Circuit Tap

Hi Wayne, thanks for the warning about the Chicago 3-way. That could explain why both the red and black conductors were landed on the same breaker.

Ryan, I don't understand what it is you are getting at. Are you suggesting that 240.20(B) requires all multiwire circuits to have handle ties?

This leads to other questions: what terminology does the code use to differentiate between multi-pole breakers and single-pole breakers with handle ties? Is there a difference between "a means to simultaneously disconnect the ungrounded conductors" [210.4(B) and 210.7(C)] and "individual single-pole circuit breakers with ... approved handle ties" [240.20(B)(1)]?

The terminology of 240.20(B) "Circuit breakers shall open all ungrounded conductors..." quite clearly requires multi-pole breakers when there is more than one ungrounded conductor. Is it possible that "a means to simultaneously disconnect the ungrounded conductors" includes both single-pole CBs with handles ties and multi-pole CBs?

The whole concept of handle ties seems suspect, since if one pole trips, the others may or may not also trip. To me, that's not the kind of uncertainty that has a place in electrical systems.

 

[ryan_618]

Re: Multiwire Branch Circuit Tap

The only time you need a multi pole breaker is when you have line to line loads.

the only time you need approved handle ties or multi pole breakers is when you have a multiwire BC on the same yoke in a dwelling, or when you have multiple circuits (not a multiwire BC) on a single yoke.

 

[hurk27]

Re: Multiwire Branch Circuit Tap

Thanks Ryan for pointing that out, but we also have multiple circuits in dwellings too so 210.7(C) Would also apply to dwellings. But you are right That I did quote the wrong article for the subject in this thread.
And I would think that 210.4 would apply to other than dwellings too, as there are multi-wire circuits in other than dwellings.

As far as splitting up a multi-wire circuit into two seperate circuits if the NEC didn't allow this we wouldn't have the services that feed our dwellings. Think about it each service is a multi-wire circuit that splits up in to many breach circuits.

[ July 20, 2004, 07:10 PM: Message edited by: hurk27 ]

 

[a.wayne3@verizon.net]

Re: Multiwire Branch Circuit Tap

To me the grounded conductor carries as much punch as the ungrounded does.ever get hit by a ballast load??As far as I am concerned if there are 2 circuits tied to a common neutral than both must be de-energized at the same time common yoke or not !!!!

 

[hurk27]

Re: Multiwire Branch Circuit Tap

Allen

if there are 2 circuits tied to a common neutral than both must be de-energized at the same time common yoke or not !!!!

But that is only your opinion Not the NEC. Which only requires handle ties when both circuits are landed on common yoke. I agree that multi-wire circuit can be a dangerous circuit if one does not understand them but getting in between a ballast can be done on a single circuit and you would most likely get hit even harder as you will receive the total circuit voltage not just the unbalance of a multi-wire circuit. This is not the danger, it's the fact that one could turn off a single pole breaker thinking he removed power from the receptacle or switch and still be electrocuted.

 

[iwire]

Re: Multiwire Branch Circuit Tap

I use these circuits all the time and it would be tough for me to always use handle ties. The breakers may not always be beside each other.

1,3,5 is nice when I can, but 1,22,29 is OK too.

Having a small amprobe is very handy to verify you are not about to open a neutral with a load on it.

 

[jimwalker]

Re: Multiwire Branch Circuit Tap

OK Allen please exsplain hazzard if not on same yoke
my thinking says i dont want lets sat the refrig tripping because a SA had a problem
Dont we all use hot sticks on repairs ?

[ July 20, 2004, 07:39 PM: Message edited by: jimwalker ]

 

[hurk27]

Re: Multiwire Branch Circuit Tap

This is also why neutrals of multi-wired circuits are not allowed to use the device as a splice point as since the NEC allows single pole breakers when a multi-wire circuit feeds receptacles not on a single yoke, removing them must not create a shock hazard.

 

[hurk27]

Re: Multiwire Branch Circuit Tap

Darn you guys type fast. LOL

 

[jimwalker]

Re: Multiwire Branch Circuit Tap

hurk27 yes but we all have seen this violated

 

[hurk27]

Re: Multiwire Branch Circuit Tap

If I'm in a romex box and see a red the first thing I do is pull the panel cover to see if there is any multi-wire circuits. On a conduit job the same things goes but looking in the panel comes first. This is why you should always remove the power first.

We had a city worker who was allowed by the city to do some remodeling in there bath room. he added some lights and a bigger exhaust fan. he just went to the first pull box that had what he thought was a single circuit (probably didn't give it a second thought) and went to connect his new circuit to the existing circuit. well when he removed the wire nut on the neutrals they fell apart. The surge that hit the 911 system fried 8 UPS and 4 computers and the control console. This cost the city about $40,000. That is just one thing that could happen with multi-wire circuits. Needless to say he wont be doing any electrical work for a while.

 

[hurk27]

Re: Multiwire Branch Circuit Tap

Jim

hurk27 yes but we all have seen this violated

So what's the point?
We cant control what others do. we must take precaution anytime we are working with a multi-wire circuit. I go one father Like Bob said double check for current on neutrals even when there is not a apparent multi-wire circuit as I have found many times some JOAT will grab a hot from one circuit and a neutral from another.

 

[jimwalker]

Re: Multiwire Branch Circuit Tap

Wrong.This is what happens when non licensed uninsured handymen do work that requires a licensed insured contractor

 

[jimwalker]

Re: Multiwire Branch Circuit Tap

I personally worry more about them neutrals than the hots

 

[iwire]

Re: Multiwire Branch Circuit Tap

This is my everyday meter it is great tool to make sure the neutral you are about to disconnect is not carrying current.

 

[roger]

Re: Multiwire Branch Circuit Tap

Jim, even if "non licensed uninsured handymen" had done this,how can a wireman with any experience look in a box, see more than one ungrounded conductor, and then not think it might be a multi-wire branch circuit and take the necessary precautions?

Let's don't go to the unexperienced or DIYer "might" get hurt conversation.

Roger