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-   -   Double-tapped breaker and MWBC (http://www.diychatroom.com/f18/double-tapped-breaker-mwbc-100469/)

sirsparksalot 04-04-2011 02:08 AM

Double-tapped breaker and MWBC
 
So, my panel has a breaker that is double tapped with a shared neutral. My recollection is that this double-tap (two hots serving two separate circuits under one breaker terminal) is illegal.

In order to fix this, what can I do? I would like to add a separate breaker for one of the circuits, and the question is: does it need to share the SAME BUS, or should it be on DIFFERENT Phases?

I have no need to scrap the MWBC, but I would like to get the two wires off the same breaker. (At this time, and per A7's advice, I've joined the Black and Red wires together with a pigtail to this one breaker. QUESTION: is this Code compliant (since it's pigtailed, and the prohibition involves only placing more than one wire under the same breaker terminal)?

Thanks again.

AllanJ 04-04-2011 08:34 AM

Must be different busses/"phases" for separate breakers.

When the cable served by that breaker is a multiwire branch circuit (two hots and one neutral) then it is actually okay if the two hots are pigtailed* and fed to the same breaker sized for one of those two hot wires. But here you are not taking advantage of the full capability of the MWBC.

You may not put the two hot wires onto separate breaker screws of a single-wide aka tandem breaker with two handles.

To separate the hot wires onto separate breakers, the two breakers need to be in a single double-wide unit with handles tied together and that snaps over two fins on opposite sides of the 120/240 volt service in the panel.

* Two wires may be connected to the same screw without use of pigtails provided that there are grooves or a retainer washer that keep the wires, assuming/pretending no pretwisting and no bending around the screw, from slipping off to the side and out from under the screw if jostled slightly before the screw is fully tightened.

oleguy74 04-04-2011 10:41 AM

don't think so.mwbc must not be on same buss.so they cannot be used on same breaker or tied together.they must be on a two pole breaker.

J. V. 04-04-2011 11:19 AM

What you have is illegal and non compliant. The first word that comes to mind is "HACK".
Remove the breaker and install a double pole breaker. There is nothing wrong with MWBC's if they are installed correctly.

By connecting the two wires together with a wire nut effectively gives you ONE circuit. This is not a MWBC. This is one circuit connected together with one wirenut.
A MWBC is two circuits in one cable sharing one neutral..

a7ecorsair 04-04-2011 02:41 PM

Just to clear things up. Sirsparky had another thread regarding range hood. At his main panel he has 1 red, 1 black, and 1 white leaving the panel through a conduit. The red and black were connected to a single breaker
Quote:

two wires were pinned to one breaker
not liking this he move one line to another breaker without knowing which leg it was attached so there was a potential of double current in the white wire.
So, he whats to make this a legal MWBC.
Sparky, to do this, you need a double pole breaker and you need to make sure all neutrals are pigtailed before they connect to a device. You will have to check all outlet boxes (lights, your range hood, and receptacle) on both circuits for this condition.

sirsparksalot 04-04-2011 03:28 PM

a7ecorsair is correct that I'm still working with my range hood circuit, and I do want to make this a legal MWBC, as it appears that that was the original intention.

A question about not using adjacent single pole breakers. I found the following partial article at: http://www.electriciansparadise.com/articles.html

Quote:

The following article was written when NEC 2005 was in force. NEC 2008 contains one significant Code change. Instead of only certain sensitive multiwire branch circuits, now all multiwire branch circuits must be protected by a double-pole breaker, not two single-pole breakers. In all cases, two single-pole breakers, linked by a listed device, are equivalent to a double-pole breaker.



The above seems contradictory to me, and the author doesn't note the NEC article he's referring to.

First he says "...not two single-pole breakers", then he states that "...two single-pole breakers, linked by a listed device, are equivalent to a [DP] breaker". I am assuming that the "listed device" is a "handle tie", and that that would make it legal. QUESTION: Can anyone verify this for me?

Now, I have SP breakers, but I'd have to go out and buy a DP, and if I could use the SPs with a handle tie, that would be good.

As a final thought, with all the work involved in a7's instructions for making this legal, would it be just as well, AND SAFE, to leave it the way it is, that is, two hots connected together with a pigtail to the one breaker?


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