Shared neutrals used anymore?

As much as I used MWBC in the past, there is no way I would remove required handle ties. They aren’t there for those of us that grew up with, them. Remove if you want while trouble shooting but put them back. That next kid may not have the slightest.
Some area ECs were installing AFCIs then taking them out after inspection. Grrr.
When I hear something similar to what you are saying, others reply and say this is why a person must be 'trained and qualified' before they start playing with electricity. This is why some electricians get paid the big bucks . lol.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
By living and working where we're still on the 2014 NEC. :cool:
Allow me to rephrase: I have only installed AFCI breakers in new construction on bedroom outlets as of yet.
The only change in coverage areas between 2014 and 2017 for AFCI was the addition of language related to dormitory units in 210.12(B)(D), other than that requirements still includes, whether 2014 or 2017, all 120V 1Ph 15/20amp branch circuit outlets or devices in kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas, or similar rooms.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Doesn't that just needlessly create a "Trouble in one circuit shut down two" situation?
Somewhat, and it is a real consideration.

Because the MWBC makes the premium for an additional circuit smaller, I end up having more circuits then I might otherwise run. So trouble in one circuits will shut down two circuits that are smaller (in terms of number of outlets served) then they would be if I'd run them as single circuits.

For example the basement receptacle run is a single MWBC where it might otherwise be a single circuit.

-Jon
 
As much as I used MWBC in the past, there is no way I would remove required handle ties. They aren’t there for those of us that grew up with, them. Remove if you want while trouble shooting but put them back. That next kid may not have the slightest.
Some area ECs were installing AFCIs then taking them out after inspection. Grrr.
I usually dont flaunt code defiance, but in this case, I will most likely be doing the additions/changes at this facility, and I know from years of working in their other labs, its an absolute nightmare to get permission to turn a circuit off. I dont think removing the tie on a given circuit to work on it is possible without turning it off (or the surrounding breakers off) because the thru rod would need to be slid out. Might depend on the specific tie construction, but as I said Siemens doesnt offer one (a three pole that is), QO off course already is single handle, not sure about GE, so that just leaves Eaton which I have seen and used for their BR line and they have the thru rod and a cap that snaps over all three handles. I guess I could skip the thru rod and just use the snap on cover.....
 
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roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Not sure I agree. The bold appears to suggest it is one circuit only in section 225.30
That is specifically telling you it must be considered one circuit for that section, in other applications it can be considered multiple circuits even though it is a single circuit.

Branch Circuit, Multiwire.
A branch circuit that consists
of two or more ungrounded conductors that have a voltage
between them, and a grounded conductor that has equal
voltage between it and each ungrounded conductor of the
circuit and that is connected to the neutral or grounded
conductor of the system.

210.4 Multiwire Branch Circuits.
(A) General. Branch circuits recognized by this article shall
be permitted as multiwire circuits. A multiwire circuit shall be
permitted to be considered as multiple circuits.
All conductors
of a multiwire branch circuit shall originate from the same
panelboard or similar distribution equipment.


Roger
 

jap

Senior Member
A MWBC is one circuit period. You simply tell the occupant you are turning off the circuit and it will kill a lot of lights and receptacles. Of course you can work it hot since the CMP put us in this situation.

Roger
I beg to differ.

Although it is considered 1 circuit by the book, a multi-wire branch circuit is exactly that, "Multi" circuits meaning more than one circuit.

I'm not talking about a scheduled shut down, but just the same, I'm talking about when the circuit trips, or, nuisance trips for that matter, it shuts down another circuit that has no problem to begin with by it's design.

Much like using a 2p common trip breaker for the handle tie rule instead of using a handle tie itself which they say wont trip both.

Using a 2p or 3p common trip breaker to cover a multi-wire branch circuit will always shut down all circuits tied to it.

A Single Phase multi-wire branch circuit tied to a common trip breaker or 2p arc fault breaker will always cause a "Trouble in one circuit shut down two" situation, so I stand by my statement.

We have enough problems trying to keep single pole arc fault circuits from tripping or nuisance tripping.

Why shut off more luxuries at a time than need be? :)

JAP>
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
I beg to differ.

Although it is considered 1 circuit by the book, a multi-wire branch circuit is exactly that, "Multi" circuits meaning more than one circuit.


JAP>
No, the book is referring to what it really is. Draw out current flow (use any numbers you like for each ungrounded conductor) in any MWBC and you will see that it is in fact a single circuit. We can play with the NEC wording but we can't change the physics of the circuit.

Here's an example.

1605624728673.png

Roger
 

Attachments

jap

Senior Member
No, the book is referring to what it really is. Draw out current flow (use any numbers you like for each ungrounded conductor) in any MWBC and you will see that it is in fact a single circuit. We can play with the NEC wording but we can't change the physics of the circuit.

Here's an example.

View attachment 2554314

Roger

A lot of good artsy technical stuff,however,it doesn't relieve the fact that if you didn't need more than one circuit, you wouldn't pull a multi-wire branch circuit in the first place.

You'd simply install a single circuit on a single pole arc fault breaker.

JAP>
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
A lot of good artsy technical stuff,however,it doesn't relieve the fact that if you didn't need more than one circuit, you wouldn't pull a multi-wire branch circuit in the first place.


JAP>
No, I'd install a single MWBC, that's all I would need, I wouldn't need multiple circuits, 210.4 and 210.7 point out they are not the same thing.

Roger
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Trying to pin down the term circuit is IMHO a rabbit hole.

If you consider a circuit to be a single closed path that electrons follow, then every parallel connected load is in fact its own circuit. Most people will call a single pole breaker supplying a set of loads connected 'hot to neutral' a single circuit, but this single circuit is composed of multiple current paths.

An MWBC is explicitly defined as a 'single circuit' for purposes of feeding a detached structure. But this explicit description only applies to this specific case.

An MWBC provides the power of two separate single circuits of the same amp rating. For purposes of 'amount of load served' it is two circuits. My microwave and toaster are on an MWBC. For purpose of being able to run the microwave and toaster at the same time, it is clearly _two_ circuits.

But this MWBC is supplied by a double pole breaker. If something has a fault, then both microwave and toaster lose power. For purposes of the number of devices shut down when something trips OCPD it is clearly a single circuit.

-Jon
 

jap

Senior Member
Trying to pin down the term circuit is IMHO a rabbit hole.

If you consider a circuit to be a single closed path that electrons follow, then every parallel connected load is in fact its own circuit. Most people will call a single pole breaker supplying a set of loads connected 'hot to neutral' a single circuit, but this single circuit is composed of multiple current paths.

An MWBC is explicitly defined as a 'single circuit' for purposes of feeding a detached structure. But this explicit description only applies to this specific case.

An MWBC provides the power of two separate single circuits of the same amp rating. For purposes of 'amount of load served' it is two circuits. My microwave and toaster are on an MWBC. For purpose of being able to run the microwave and toaster at the same time, it is clearly _two_ circuits.

But this MWBC is supplied by a double pole breaker. If something has a fault, then both microwave and toaster lose power. For purposes of the number of devices shut down when something trips OCPD it is clearly a single circuit.


-Jon

Exactly.

JAP>
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
But this MWBC is supplied by a double pole breaker. If something has a fault, then both microwave and toaster lose power. For purposes of the number of devices shut down when something trips OCPD it is clearly a single circuit.

-Jon
I know you know this Jon but here goes, even though a double pole breaker is the common way most MWBC's are protected it doesn't have to be, common tripping is not the intent, common disconnecting is the reason. You could use single pole breakers with handle ties.

Roger
 

jap

Senior Member
No, I'd install a single MWBC, that's all I would need, I wouldn't need multiple circuits, 210.4 and 210.7 point out they are not the same thing.

Roger
You would "combine" both loads and install a single MWBC on a 2 pole breaker to feed "both" loads because (1) branch circuit feeding both loads from a single pole branch circuit would have to be much larger.

That's the beauty of a Multi-Wire branch circuit, and , perfectly legal.

In doing that, you do fall into the "Trouble in one shut down both" scenario.

There's no way around it.

Just because you can doesn't always mean you should.

What you gain in one aspect you loose in another is all I'm saying.

JAP>
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I know you know this Jon but here goes, even though a double pole breaker is the common way most MWBC's are protected it doesn't have to be, common tripping is not the intent, common disconnecting is the reason. You could use single pole breakers with handle ties.
True, and I'd actually forgotten this.

But as a practical matter: my point of entry to this thread was that I started using MWBC when I discovered double pole AFCI devices available for my panel. I don't believe that single pole AFCI devices are available for my panel that will function with MWBCs.

I know that single pole AFCI devices that work with MWBCs exist. However by their nature such devices can't have ground fault functionality. I believe that ground fault functionality provides more safety benefit than trying to reliably detect arc signatures, so if I am going to have to deal with the cost and trouble of AFCI devices, I actually want that ground fault function.

So for my specific usage MWBC usage forces the common trip issue.

-Jon
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
You would "combine" both loads and install a single MWBC on a 2 pole breaker to feed "both" loads because (1) branch circuit feeding both loads from a single pole branch circuit would have to be much larger.
Actually looking back at you post #29, of course if I only needed a single pole OCPD I would only install a two wire circuit.

Roger
 

jap

Senior Member
True, and I'd actually forgotten this.

But as a practical matter: my point of entry to this thread was that I started using MWBC when I discovered double pole AFCI devices available for my panel. I don't believe that single pole AFCI devices are available for my panel that will function with MWBCs.

I know that single pole AFCI devices that work with MWBCs exist. However by their nature such devices can't have ground fault functionality. I believe that ground fault functionality provides more safety benefit than trying to reliably detect arc signatures, so if I am going to have to deal with the cost and trouble of AFCI devices, I actually want that ground fault function.

So for my specific usage MWBC usage forces the common trip issue.

-Jon
You have a gift of explaining things in a way that makes sense.

JAP>
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
True, and I'd actually forgotten this.

But as a practical matter: my point of entry to this thread was that I started using MWBC when I discovered double pole AFCI devices available for my panel. I don't believe that single pole AFCI devices are available for my panel that will function with MWBCs.

I know that single pole AFCI devices that work with MWBCs exist. However by their nature such devices can't have ground fault functionality. I believe that ground fault functionality provides more safety benefit than trying to reliably detect arc signatures, so if I am going to have to deal with the cost and trouble of AFCI devices, I actually want that ground fault function.

So for my specific usage MWBC usage forces the common trip issue.

-Jon
And I must clarify that I was commercial and industrial, not in the residential market.

Roger
 
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kwired

Electron manager
Location
NE Nebraska
Allow me to rephrase: I have only installed AFCI breakers in new construction on bedroom outlets as of yet.
2014 requires AFCI in more than just bedrooms, you maybe have some amendments? Pretty sure 2008 was when they expanded to more than just bedrooms, and have added a little more every so often since.
 

kwired

Electron manager
Location
NE Nebraska
I wired a restaurant last year, and bought handle ties for all my 2-and 3-pole mwbc. Eaton panels.

When I got final inspection, the AHJ noted that I didn't have many single pole breakers, and asked what gives. So I explained to him that I handle-tied my mwbc.

Him: what did you do that for? 🤔🧐
Me: 🤔 'cause it's required
Him: not here
Me: ok....so....ima take 'em off...?
Him: I would

Done
OK. Unless they actually have an amendment it had been in code for a while even back in 2011/2014 or whatever code you said applied. think this went into effect for all MWBC's in 2002 or maybe 2005 at the latest.
 
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