MWBC - Should I?

[Spudland_Dave]

In doing homework for my garage build, I had a few people tell me to use Duplex Boxes and install 2 sets of Recept's on 2 seperate circuits...especially over on my "workshop" side of the building. In thinking about this, rather then run 2 12-2's to each box...thinkin of using a single 12-3 and doing it that way...I am aware I need 2 breakers, one on each leg of the 220V...
Should I or shouldnt I?

 

[pattenp]

The thing is you need to use a double pole breaker on a MWBC. The con is if you trip one side, both sides will trip. The only advantage is saving $$ on wire. I personally wouldn't use MWBCs.

 

[Spudland_Dave]

The thing is you need to use a double pole breaker on a MWBC. The con is if you trip one side, both sides will trip. The only advantage is saving $$ on wire. I personally wouldn't use MWBCs.

Kinda defeats the purpose then, thanks for that input..IMO the whole point of 2 seperate circuits would be to prevent the tripping... Might as well just do it old school...duplex box 1 circuit.

 

[Charles (in GA)]

MWBC is suitable for certain specialized functions, such as when I used it for lighting. For general purpose circuits for receptacles, don't bother, it isn't worth the hassles and future problems.

Charles

 

[pattenp]

The MWBC has its place, but I just don't see any benefit of it in a workshop for general use outlets.

Charles beat me to the punch.

 

[madosta]

The MWBC has its place, but I just don't see any benefit of it in a workshop for general use outlets.

Charles beat me to the punch.

What about if you have an 8 space sub panel, you have 5 handles already and two empty spots?

 

[lakee911]

The thing is you need to use a double pole breaker on a MWBC. The con is if you trip one side, both sides will trip. The only advantage is saving $$ on wire. I personally wouldn't use MWBCs.

Actually you don't need to use a 2-pole breaker for a MWBC. This is where a tie handle on two 1-pole breakers is permitted. The tie handle provides common disconnect but single trip. You will need to open both sides, though, to reset and reclose the breaker.

I think it's a good application ... better than sending the two legs off to different parts of the building.

 

[pattenp]

Actually you don't need to use a 2-pole breaker for a MWBC. This is where a tie handle on two 1-pole breakers is permitted. The tie handle provides common disconnect but single trip. You will need to open both sides, though, to reset and reclose the breaker.

I think it's a good application ... better than sending the two legs off to different parts of the building.

You bring up a good point. A double pole breaker is two single pole breakers that are mechanically tied together. I thought DP is no different than two single poles with a handle tie. Now your comment on only one side will trip is not how I understand it. I thought a DP or 2 SP's with handle ties will trip both sides on an overload of one leg.

Edit: Did some research and you are right on the single pole with handle ties only tripping one side. The double pole are common trip which means both sides trip on an overload.

So Dave if you use two singles with handle ties it makes more sense now to do the MWBC for the outlets. Live and learn.

 

[madosta]

You bring up a good point. A double pole breaker is two single pole breakers that are mechanically tied together. I thought DP is no different than two single poles with a handle tie. Now your comment on only one side will trip is not how I understand it. I thought a DP or 2 SP's with handle ties will trip both sides on an overload of one leg.

Edit: Did some research and you are right on the single pole with handle ties only tripping one side. The double pole are common trip which means both sides trip on an overload.

So Dave if you use two singles with handle ties it makes more sense now to do the MWBC for the outlets. Live and learn.

I learn a lot from this pattenp dude. Such as this. Woo!

 

[Spudland_Dave]

I learn a lot from this pattenp dude. Such as this. Woo!

Join the club!
So this would be what I need for my panel...
http://www.homedepot.com/buy/square-d-by-schneider-electric-homeline-circuit-breaker-handle-tie-hom1htcp.html

Amazingly it says right in the description "Converts any 2 adjacent 120/240 VAC single breakers to an independent trip 2-pole circuit breaker"

So looks like it may be a great way to go...save a few bucks on wire, 2 seperate circuits, etc...

 

[pattenp]

I learn a lot from this pattenp dude. Such as this. Woo!

Thanks, but Lakee911 needs to get the credit on this one.

 

[pattenp]

Join the club!
So this would be what I need for my panel...
http://www.homedepot.com/buy/square-d-by-schneider-electric-homeline-circuit-breaker-handle-tie-hom1htcp.html

Amazingly it says right in the description "Converts any 2 adjacent 120/240 VAC single breakers to an independent trip 2-pole circuit breaker"

So looks like it may be a great way to go...save a few bucks on wire, 2 seperate circuits, etc...

If that is the breaker you have then those are the ties you need.

You can send me half your savings.

 

[jvitez]

I've got multiple MWBC's in my house. Residential electricians seem to like it here. This includes several attached circuits. I'm under the CEC not NEC, but my garage MWBC's are single pole breakers without any handle ties. I'll have to check the CEC and see if the electricians were lazy or the CEC is different in this regard.

 

[Charles (in GA)]

With the exception of Square D QO breakers, all other double poles are simply the single pole breakers riveted together with a handle tie permanently made on to them. There is not internal connection between them. When one goes, it takes the other with it. You want both sides dead when you are going to work on the circuit and this is why the NEC requires the handle tie or double pole breaker. Fact is a double pole costs about the same price as two single poles, and you add in the price of a package of handle ties and its more expensive to use the single poles on the MWBC.

Handle ties are rigid metal or plastic pins that pass all the way thru the holes in the handles, or are metal sleeves that rigidly clamp on the handles. If one trips, it is going to take the other with it.

Its a mountains out of mole hills thing, just use the double pole breaker and be done with it or don't use the MWBC.

I'd be interested to see any manufacturers information you could provide that has information to the contrary.

Charles

 

[Spudland_Dave]

If that is the breaker you have then those are the ties you need.

You can send me half your savings.

Indeed it is...Sq D Homeline in both House & Garage...for the sake of simplicity, I plan on another Homeline when I put the 60A Sub in..

I'd be interested to see any manufacturers information you could provide that has information to the contrary.

Charles

I see what your saying and kinda had the same feeling looking at it from a "Mechanical" perspective...How could they indpendently trip...but I guess I get/got confused by the wording "Converts any 2 adjacent 120/240 VAC single breakers to an independent trip 2-pole circuit breaker"

 

[pattenp]

Charles I know where you're coming from and that is why I said what I did at first. But after some web searching I was getting info to the contrary on the common trip DP vs two singles with ties. I'm not sure if it's a thing from brand to brand that the physical throw of the handle on an overload takes the other handle with it. I've noticed on some breakers it's hard to tell they're tripped because the handle is barely over from the full on position. I would really like to get some different brands of breakers and do some type of a bench test to see what is what.

 

[Spudland_Dave]

Charles I know where you're coming from and that is why I said what I did at first. But after some web searching I was getting info to the contrary on the common trip DP vs two singles with ties. I'm not sure if it's a thing from brand to brand that the physical throw of the handle on an overload takes the other handle with it. I've noticed on some breakers it's hard to tell they're tripped because the handle is barely over from the full on position. I would really like to get some different brands of breakers and do some type of a bench test to see what is what.

Looking at the way these are made, I guess you may be onto something...there would appear to be enough slack to allow just such a thing. Also, why wouldnt they just sell the plastic handle thingie which you would just pop on, like the factory 2 pole breakers... "Why Reinvent The Wheel" comes to mind.
Actually the more I think about the mechanics of this, you may be exactly right...allows for independent trip, yet shutting the breaker off will shut both.

 

[jbs]

One other, albeit minor, advantage of a MWBC is that it can limit voltage drop on a long run. In the case that both halves are equally loaded, you essentially have only an one-way trip for the current one each leg. Hence, best case scenario is half the normal (round-trip) voltage drop.

 

[MrMark]

I think the handle tie between the homeline single poles (it's a metal rod) will allow one breaker to trip but not take the other with it. There is a good amount of slop there.