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Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
Even though you need to handle tie or provide multi pole breaker when using MWBC I would still think it would be cheaper than a job where you had to install dedicated neutrals. IMO it would be a lot more copper depending on the magnitude of the work. Agree?
 
MWBC's will save money even if you have to buy and install handle ties. It's funny because when the simultaneous disconnect rule went into effect engineers just banned MWBC'S and went with separate neutrals. Now with the cost of copper some may be rethinking that strategy.
 
The down side of MWBCs comes into play when two or more users end up sharing the circuit (as opposed to several outlets all assigned to the same user). Take an office for example. If you need to turn off a circuit for maintenance or repair of one user's equipment, other users will be without power during the work. That may prove too disruptive (i.e., too costly) to the overall productivity of the office. That is why I almost always called out separate neutrals, that and the fact that most of my clients forbade MWBCs.
 
M dubs have their place. Probably don't agree with Charlie as that sounds like the lazy way around it. But very true that the safer play is send a dedicated neuty. Reality is people like to dream up all the bad things with M dubs, but with even a little planning, you should not be blowing breakers or doing "circuit maint" daily. Is it a friggin server room?

One of the sweethearts of this play is 120/240 on the same cirqweet. Just means you have a few options for basic loads. Wire a little shop and can toss a 240V recep for a guys drill press. Works great. I also like that I can run 3/c on half the run, then step it to 2/c on the other half unless 240V is desired on the entire circuit.

Lots of options, but probably more design work, thus why people run from it. And I can get that if you just want to future proof everything. But that's also why we pull spare electricon party sticks in the pipe when built.
 
Obviously can't speak for other colocation providers, but you won't see a shared neutral at ours. We'd never hear the end of it if we had to take one customer down because their neighbor needed work done (as charlie mentions), and the risk of one customer's malfunctioning gear throwing triplens (or worse, tripping the breaker on failure) and causing issues for another customer just isn't worth the copper saved.
 
ModbusMan said:
Obviously can't speak for other colocation providers, but you won't see a shared neutral at ours. We'd never hear the end of it if we had to take one customer down because their neighbor needed work done (as charlie mentions), and the risk of one customer's malfunctioning gear throwing triplens (or worse, tripping the breaker on failure) and causing issues for another customer just isn't worth the copper saved.
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That's where you're throwing BIG wrenches in the mix! I work large, multi bld complexes, but same owner and company. TOTALLY different if separated "tenant" spaces. Like that is BIG! I would totally understand someone losing their mind (rightfully) to lose power to fix a neighbor issue that is not POCO related.

We talking different terms man. I've literally been there where the hair salon they were told they will lose power because the fried rice joint next to them needed work. Not going into the legals on that one, but I would be pissed too!
 
fastline said:
We talking different terms man. I've literally been there where the hair salon they were told they will lose power because the fried rice joint next to them needed work. Not going into the legals on that one, but I would be pissed too!
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Ouch... First question in my mind on that one is "Why no separate disconnects + meters???"
 
ModbusMan said:
Ouch... First question in my mind on that one is "Why no separate disconnects + meters???"
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I'm not going racial but lets say that some tenants don;t understand this stuff, and landlords don't know or don;t care. Reality is where I've seen shared spaces become separate and no one did the study.......because that costs money......Then you pay an atty, court fees, etc, etc.

Bottom line, own ALL your MWBC cirqweet. I like em, in the right applications.
 
I recently had to run four 20A circuits around a space for receptacles. All I did was change the boxes to 1900s, I used the existing 1/2" EMT. No way would I attempt to pull eight #12s through 40 foot with bends. Bad enough I pulled 6 using MWBCs. Unfortunately all I had was solid but lots of pulling lube. :(

-Hal
 
Alwayslearningelec said:
Even though you need to handle tie or provide multi pole breaker when using MWBC I would still think it would be cheaper than a job where you had to install dedicated neutrals. IMO it would be a lot more copper depending on the magnitude of the work. Agree?
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I would say its not so much the copper savings, the big savings come from the # of CCC you can get in a conduit. Consider that in a three-quarter EMT one can get nine circuits using MWBC's. Without MWBC's you would need more than twice the number of conduits to avoid derating.

Also, make sure to use single poles with handle ties and not 3 pole breakers for more cost savings (and so you can pop the handle tie off if you want to just turn off one circuit 😇)
 
You can also run all the MWBC's to a group of boxes in a ceiling location and install switches in order to isolate each part of the circuit.
 
I like Electrofan's point about # of current carrying conductors, but the issue I see especially since we are 10 years down the road from seeing MWBC's regularly is that our work force is NOT what it once was. In order to have 2 or 3 MWBC's in the same home run without mixing up the neutrals AND make sure the shared circuits are side by side in the panel to accept handle ties you are asking too much of many of our "electricians". Sorry to say.
 
Strathead said:
In order to have 2 or 3 MWBC's in the same home run without mixing up the neutrals AND make sure the shared circuits are side by side in the panel to accept handle ties you are asking too much of many of our "electricians".
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If they cannot accomplish that simple task I wouldn't even call them an electrician. Having said that I can see it happening in certain places where unskilled hacks are the norm.
 
electrofelon said:
Also, make sure to use single poles with handle ties and not 3 pole breakers for more cost savings (and so you can pop the handle tie off if you want to just turn off one circuit 😇)
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I will have to take issue with this notion. It defeats the safety feature that is the reason for requiring handle ties in the first place.
 
I am not seeing any real disagreements here. There are pros and cons that should be evaluated before making a decision to use, or not to use, MWBCs.
 
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