Exisitng MWBC

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maloo

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Marion, Iowa
Is there a code that requires you to tie a MWBC together for an existing circuit? I have two sets of MWBC (Phase ABC and a grounded) that were installed prior to requirements and abandoned to a Jbox. So if I use these existing circuits do I have to install breaker ties or three pole breakers? I would personally but my boss thinks different.

I know there are similar codes for replacing residential receptacles with TR's and exterior receptacles with WR's just have not found anything about MWBC's.

Thanks
 
Personally I don't think there is a clear cut answer. I think it will be up to the inspector but I tend to see it your way.
 
IMO, which isn't worth much, I would say that the circuit is now used and must have handle ties or a 3 pole breaker. I also agree with Bob that it is an AHJ call. Handle ties are cheap...
 
Dennis Alwon said:
IMO, which isn't worth much, I would say that the circuit is now used and must have handle ties or a 3 pole breaker. I also agree with Bob that it is an AHJ call. Handle ties are cheap...
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As an inspector I agree with Dennis. The existing MWBC was abandoned, but now is going to be used for something [thus changed in some way, modified, extended] - any new work you do to a circuit must comply with the code at the time the work is done.... kind of like the receptacle example - if you replace an existing 3 prong receptacle [damaged, whatever] the new receptacle must meet today's code requirements.
 
In addition to the tie handle that have mentioned, the conductors of a MWBC family must also be tied together in the panel.
 
I tend to be conservative in my thinking on these issues. I believe the more conservative view would be to require handle ties and grouping of the multi wire circuit.

But I would agree with your boss on this one. First the circuit most likely wasn?t abandoned but left for future use. Second I would look for some precedent in the code that might give guidance. I turned to cancelled knob and tube for a wiring method that doesn?t meet current installation standards but still can be extended and used.

And as others pointed out the multi wire circuit in past code cycles did not have to be group together. It may not be as simple as adding handle ties to single pole breakers. You may have to rearrange breaker positions in the panel to accomplish being able to handle tie the breakers in the panel.
 
david said:
But I would agree with your boss on this one. First the circuit most likely wasn?t abandoned but left for future use.
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Even if this were true they are now, in some way, modifying that existing wiring.

Scenario: Existing 3-wire, 240v, no EGC to electric range...not being used. For a kitchen remodel they need to move this existing circuit 2 ft. to the right. Same FMC conduit being used, same conductors, same outlet box, same outlet - but once he moves the outlet to as new location the circuit must comply with current codes [EGC installed].

Why wouldn't the modification of an existing MWBC require compliance with current codes?
 
dana1028 said:
Even if this were true they are now, in some way, modifying that existing wiring.

Scenario: Existing 3-wire, 240v, no EGC to electric range...not being used. For a kitchen remodel they need to move this existing circuit 2 ft. to the right. Same FMC conduit being used, same conductors, same outlet box, same outlet - but once he moves the outlet to as new location the circuit must comply with current codes [EGC installed].

Why wouldn't the modification of an existing MWBC require compliance with current codes?
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I agree in principle, in practice, and in general.

However I've never been clear on where exactly the NEC clause is that triggers this. Seems like something that is almost never written in the NEC, rather a requirement imposed by the local AHJs.
 
dana1028 said:
Even if this were true they are now, in some way, modifying that existing wiring.

Why wouldn't the modification of an existing MWBC require compliance with current codes?
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He is not modifying an exisitng circuit he making use of a code compliant instalation. The code was never met to be retroactive. Engineers designed spare circuits and the owners paid good money to have them installed for the purpose of future use. If you make the code retroactive how far do you go, where do you stop at?
 
edward said:
In addition to the tie handle that have mentioned, the conductors of a MWBC family must also be tied together in the panel.
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Only if it's not evident which neutral conductor they share. You would only need to group them together, if say, you were running several MWBC's in one conduit. You don't nee to do it if you used MC cable.

You would also need to do it if you were running a neutral with each circuit, which some EC's are doing rather than tying the breakers together.
 
dana1028 said:
As an inspector I agree with Dennis. The existing MWBC was abandoned, but now is going to be used for something [thus changed in some way, modified, extended] - any new work you do to a circuit must comply with the code at the time the work is done.... kind of like the receptacle example - if you replace an existing 3 prong receptacle [damaged, whatever] the new receptacle must meet today's code requirements.
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I would probably make them upgrade it too.
 
david said:
He is not modifying an exisitng circuit he making use of a code compliant instalation. The code was never met to be retroactive. Engineers designed spare circuits and the owners paid good money to have them installed for the purpose of future use. If you make the code retroactive how far do you go, where do you stop at?
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The circuit, IMO, is now existent since there is nothing wired to it. Once you add a load to the circuit , again IMO , you have made it a circuit and must comply with the NEC.
 
Thanks everyone for your time and input. Seems like a good argument starter over a couple of breaker ties. That is assuming you can tie three Square D QO breakers together with ties. Havn't taking the time to look that one up yet.
 
maloo said:
Thanks everyone for your time and input. Seems like a good argument starter over a couple of breaker ties. That is assuming you can tie three Square D QO breakers together with ties. Havn't taking the time to look that one up yet.
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Yes, they do make a three pole handle tie. Whether or not you can find it in town is another matter . . .
 
Two questions regarding posts on this topic.
1. If I install multiple multiwire branch circuits in a conduit in lieu of taping them together at the panel end and what not would it be allowable to tag the neutral conducter with the various circuit numbers? For example 2 4 6 on one and 1 3 5 on the other which clearly identifies it which I believe to be the intent. Correct or not?
2. Can I use two single handle ties to tie three breakers together?
Thanks
Chris
 
cmreschke said:
Two questions regarding posts on this topic.
1. If I install multiple multiwire branch circuits in a conduit in lieu of taping them together at the panel end and what not would it be allowable to tag the neutral conducter with the various circuit numbers? For example 2 4 6 on one and 1 3 5 on the other which clearly identifies it which I believe to be the intent. Correct or not?
2. Can I use two single handle ties to tie three breakers together?
Thanks
Chris
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1. I think that would be an ahj call. It seems okay but tie them together is probably easier.

2. Two single pole ties are not listed for a 3 pole connection so I would say "NO" - not compliant.
 
david said:
He is not modifying an exisitng circuit he making use of a code compliant instalation. The code was never met to be retroactive. Engineers designed spare circuits and the owners paid good money to have them installed for the purpose of future use. If you make the code retroactive how far do you go, where do you stop at?
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The OP indicated these 'conductors' had been installed previously and possibly abandoned. He made no mention of them being utilized [hooked up to equipment, components, etc.]. I got the impression that only conductors were in a j-box.

If someone is going to use these conductors today then, again I am assuming, these conductors must be connected to some piece of utilization equipment. That is the modification I am talking about. Once you start hooking up equipment to conductors you have changed the original condition [unused conductors in a j-box]. So, today you must comply with the requirements for installation the equipment [termination requirements, grounding requirements, sizing of OCP requirements]. If you must comply with all these other requirements at the time of making use of the conductors, why would you be exempt from complying with the type of OCP device [i.e. MWBC breaker requirement].
 
dana1028 said:
The OP indicated these 'conductors' had been installed previously and possibly abandoned. He made no mention of them being utilized [hooked up to equipment, components, etc.]. I got the impression that only conductors were in a j-box.

If someone is going to use these conductors today then, again I am assuming, these conductors must be connected to some piece of utilization equipment. That is the modification I am talking about. Once you start hooking up equipment to conductors you have changed the original condition [unused conductors in a j-box]. So, today you must comply with the requirements for installation the equipment [termination requirements, grounding requirements, sizing of OCP requirements]. If you must comply with all these other requirements at the time of making use of the conductors, why would you be exempt from complying with the type of OCP device [i.e. MWBC breaker requirement].
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I?ll try and illustrate it this way. Let?s say and existing multi wire circuit using circuits breakers 1-9-24 this panel is existing and its full all breakers are used. The owner wants to install one additional light. So I take a piece of mc cable. Go to a junction box and extend circuit 9 to this one light. I modified the circuit by extending it to this one light. To me the codes not retroactive so I apply current codes to the Mc cable that I ran and to the light fixture I installed. You seem to be implying that I have to rearrange the circuits in this panel to say circuits 1-3-5 and then handle tie them together and group them in the panel. To do that I would have to go to every junction box and reliable the wire markers to identify them as circuits 1-3-5. I would also have to do that to every circuit I touched to get the panel arrangement that I needed to group these circuits together.
To me the code is not retroactive I can use an existing multi wire circuit 1-9-24 even if I modify it by extending it to a new light.
 
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