multiwire branch circuit

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dukelomas

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i have recently bought " Understanding the National Electrical Code" volume 1 art 90-450 2008

my questions is with page 68 figure 210-4. am i to understand that if i have a 12-3 nm, with each ungrounded conductor going to its own receptical, on its own 20amp single pole breaker that i would have to install a handle tie to simultaneously trip both receptical? i am confused with the pictoral figure...
 

roger

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You are correct that it would require a handle tie but it is not for simultaneously tripping, it is for simultaneously opening both conductors from the source if they were "manually" operated.


Roger
 

infinity

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The NEC no longer feels that we're qualified to work on MWBC's so they've made it that all circuits that are sharing a neutral are disconnected at the same time, hence the handle tie on the CB's. This is a measure of safety that has been debated here before with some feeling that it makes it less safe since people will not be shutting off two or three circuits at a time but will instead work on that one circuit while it's still energized.
 

ivsenroute

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Location
Florida
The NEC no longer feels that we're qualified to work on MWBC's so they've made it that all circuits that are sharing a neutral are disconnected at the same time, hence the handle tie on the CB's. This is a measure of safety that has been debated here before with some feeling that it makes it less safe since people will not be shutting off two or three circuits at a time but will instead work on that one circuit while it's still energized.
I don't think it is about "qualified electricians" working on these systems but the fact that there is a large population of residential DIYs that will be working on their own home that may have a shared neutral system.

I am still of the opinion that the MWBCs should be limited to commercial applications and not single family residences because of the DIY community who often has absolutely no clue. My opinion only.
 

infinity

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I don't think it is about "qualified electricians" working on these systems but the fact that there is a large population of residential DIYs that will be working on their own home that may have a shared neutral system.

I am still of the opinion that the MWBCs should be limited to commercial applications and not single family residences because of the DIY community who often has absolutely no clue. My opinion only.
I'm not so sure that their aim was only DIYer's. I would bet that more electricians in commercial settings are hurt or killed by MWBC's than DIYer's. If that was thier sole aim they could have made this only apply to dwellings.
 

480sparky

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Iowegia
I don't think it is about "qualified electricians" working on these systems but the fact that there is a large population of residential DIYs that will be working on their own home that may have a shared neutral system.

I am still of the opinion that the MWBCs should be limited to commercial applications and not single family residences because of the DIY community who often has absolutely no clue. My opinion only.
I would like to know why the NEC, given the language in 90.1(c) and the definition of a 'qualified person', is trying to cater to DIYers then.

As to your opinion that MWBCs should be limited to commercial apps, have you ever worked in a bar? Geez, those bar owners do just a bad of a job in the pub as they do at home.

A 'qualified electrician' should know how to recognize, identify, and properly handle MWBCs, no matter where they are installed. It doesn't take too many IQ points to open a box and see a red, black, blue, green and white and know what you've got. Pull a duplex out of a box and it's got fours wires connected to four terminals. Hmmm.....
 

pete m.

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Ohio
I would like to know why the NEC, given the language in 90.1(c) and the definition of a 'qualified person', is trying to cater to DIYers then.

As to your opinion that MWBCs should be limited to commercial apps, have you ever worked in a bar? Geez, those bar owners do just a bad of a job in the pub as they do at home.

A 'qualified electrician' should know how to recognize, identify, and properly handle MWBCs, no matter where they are installed. It doesn't take too many IQ points to open a box and see a red, black, blue, green and white and know what you've got. Pull a duplex out of a box and it's got fours wires connected to four terminals. Hmmm.....
I think another one that is a little ambiguous is 110.16. The verbiage there states that it is to warn "qualified persons". Also there is a proposed 110.24 for the 2011 NEC that will require the available fault current for a given system be posted on the equipment.

Pete
 

augie47

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Duke, Welcome to the Forum.
See what we can do with a simple question :)
As Roger stated, handles ties (or simutaneous disconnecting means) are required on MWBCs
 

480sparky

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Location
Iowegia
Exactly - The NEC is NOT written for DIY'ers... DIY'ers probably dont even know what the NEC is! :roll:

~Matt
And you think WE know what it is? :D:D:D

Crikey, even WE can't understand parts of it. ;)

DIYers probably think it's just some scam book designed to make us charge them more.
 

TOOL_5150

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Location
bay area, ca
And you think WE know what it is? :D:D:D

Crikey, even WE can't understand parts of it. ;)

DIYers probably think it's just some scam book designed to make us charge them more.
hahaha that is true sometimes. Occasionally, im reading through it, and then stop and think "what the hell did i just read" :D

~Matt
 
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