3 phase branck circuits must have seperate neutrals??

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Sparkyrob11

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I'm working with a gentleman that's been an electrician much longer than I have, and he said today that it's no longer allowed to share a neutral for a 3 phase branch circuit. I hadn't heard this & wasn't sure why he would think this. Thanks for your input!
 
roger

roger

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It's not true, MWBC's are alive, well, and allowed per the NEC. Some trade people are afraid of them due to the "what if" possibility but, they are allowed.

As of the 2008 NEC, when they are used a means to manually open all ungrounded conductors that are part of the MWBC simultaneously must be provided, this is nothing more than an act to cater to DIYers IMO.

Roger
 
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Sparkyrob11

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I think I'm inclined to agree with the hesitant tradesmen in this case. Its a hospital remodel, I don't wanna share neutrals, but ultimatley, its the boss's call. Just wondering if I was gonna be able to make a good case. There's gonna be a lot of different types of equipment involved, but sometimes it's difficult to look beyond code.
 
roger

roger

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The majority of my career has been in hospitals and I have always used MWBC's and have no reservation using them. The current code has just created waste and design problems in Health Care Facilities.

Use MWBC's and sleep well.

Roger
 
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Karl H

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If you've been trained how to make a good splice and can perform it well
you will be fine. I have installed thousands of MWBC and never had a failure.
It's when you have to work with other peoples MWBC's that can't make a
proper splice. That's when I've ran into problems.

I'm a "Twister" I don't care what others think. Proof is in the pudding! :grin:
 
480sparky

480sparky

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MWBCs may have limited uses in dwellings due to two factors.

1. The high number of AFCI-protected circuits and
2. Currently, only Siemens offers a 2-pole AFCI breaker.

MWBCs cannot be used on two single-pole AFCI breakers.
 
iwire

iwire

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480sparky said:
MWBCs may have limited uses in dwellings due to two factors.

1. The high number of AFCI-protected circuits and
2. Currently, only Siemens offers a 2-pole AFCI breaker.

MWBCs cannot be used on two single-pole AFCI breakers.
Click to expand...

Not many AFCIs being used on three phase circuits.
 
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Sparkyrob11

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iwire said:
And it's always easy to spend others money.
Click to expand...

That's a great point.

I was thinking of the mixing of linear & non linear loads... but the job looks like it's well engineered & there aren't too many recepts. per circuit. I'm just overthinkin' it. The fellas statement (the guy I'm working with) made me start thinking about it a little more, that's all.
 
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roger

roger

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lakee911 said:
I'm a tie handle person myself. If I'm not mistaken, a 2P or 3P on a MWBC will kill all circuits in the event of a fault. A tie handle allows for a common disconnect and individual trip. No?
Click to expand...

You are correct, there is no requirement for common trip.

Roger
 
mxslick

mxslick

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Location
SE Idaho
lakee911 said:
I'm a tie handle person myself. If I'm not mistaken, a 2P or 3P on a MWBC will kill all circuits in the event of a fault. A tie handle allows for a common disconnect and individual trip. No?
Click to expand...

Yep, but it brings up an interesting set of problems:

First, how can you tell which pole tripped? (other than Sq D with the Visi-Trip(r) indicators.)

Second, to do a reset you have to kill the other two poles while resetting the one that tripped.

MWBC's have their place, but for those two reasons and others that I have had lengthy debates here about, I do not allow MWBC's to be used when supplying my audio and video equipment racks.
 
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lakee911

Senior Member
Location
Columbus, OH
mxslick said:
Yep, but it brings up an interesting set of problems:

First, how can you tell which pole tripped? (other than Sq D with the Visi-Trip(r) indicators.)
Click to expand...

Personally, I only use those. Spec-wise, can't typically sole source.

mxslick said:
Second, to do a reset you have to kill the other two poles while resetting the one that tripped.
Click to expand...

Good point. I guess you could take off the tie handle temporarily, no?

mxslick said:
MWBC's have their place, but for those two reasons and others that I have had lengthy debates here about, I do not allow MWBC's to be used when supplying my audio and video equipment racks.
Click to expand...

I try to stay away too.
 
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