3 phase multiwire branch circuits

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Although you could get away with as few as 4 ungrounded conductors, and 2 grounded conductors with the EMT as the ground, in this application I would run 4 Hots 4 neutrals and one ground wire. the reasons being that wow multiwire Branch circuits are certainly elegant, the fourth circuit kind of bugs that up. Yes, you will use more wire in this case however you can put those for circuits in the panel anywhere they may fit, and there may not be room in the existing panel to put a triple pole breaker in. if you use a neutral for each circuit, you don't have to worry about some idiot down the road breaking the neutral and sending higher than intended voltage to one or more phases. Also, while and EGC is not needed here, I'm of the camp that redundancy is good, and I have seen too much EMT improperly assembled or damaged, or corroded that it as a ground path would be compromised

although not applicable to your installation, many job specs now forbid multiwire Branch circuits, and for the reasons I mentioned.

on the extremely off-chance that you are installing medical equipment in a hospital, not only will you need and EGC you will need a second ground pathway as well.

, PS Welcome to The Forum aren't you glad you asked the question now LOL

edited to add... no matter if you use 6 current carrying conductors orate here 6 wires or 9 you're still within fill limits and can still use 20 amp Breakers either way.. it's a matter of personal preference and your existing set up really
 
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JFletcher said:
Although you could get away with as few as 4 ungrounded conductors, and 2 grounded conductors with the EMT as the ground, in this application I would run 4 Hots 4 neutrals and one ground wire. the reasons being that wow multiwire Branch circuits are certainly elegant, the fourth circuit kind of bugs that up. Yes, you will use more wire in this case however you can put those for circuits in the panel anywhere they may fit, and there may not be room in the existing panel to put a triple pole breaker in. if you use a neutral for each circuit, you don't have to worry about some idiot down the road breaking the neutral and sending higher than intended voltage to one or more phases. Also, while and EGC is not needed here, I'm of the camp that redundancy is good, and I have seen too much EMT improperly assembled or damaged, or corroded that it as a ground path would be compromised

although not applicable to your installation, many job specs now forbid multiwire Branch circuits, and for the reasons I mentioned.

on the extremely off-chance that you are installing medical equipment in a hospital, not only will you need and EGC you will need a second ground pathway as well.

, PS Welcome to The Forum aren't you glad you asked the question now LOL

edited to add... no matter if you use 6 current carrying conductors orate here 6 wires or 9 you're still within fill limits and can still use 20 amp Breakers either way.. it's a matter of personal preference and your existing set up really
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That second path must be the wiring method itself and not just any second path.
 
JFletcher said:
if you use a neutral for each circuit, you don't have to worry about some idiot down the road breaking the neutral and sending higher than intended voltage to one or more phases.
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It's good to know that if a service neutral gets severed somehow that your neutral pulled for every branch circuit will somehow make for a worry free situation.


JAP>
 
jap said:
It's good to know that if a service neutral gets severed somehow that your neutral pulled for every branch circuit will somehow make for a worry free situation.


JAP>
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With severing a neutral or feeder neutral you often won't have as extreme of voltage changes because of the higher chance of more balance on a service/feeder then on an individual MWBC. But that don't mean you can be assured of better balance either. I see this not only on three phase wye, but also single phase three wire. Someone loses main neutral and only has somewhat minor voltage issues, that is because of what load balance there is plus what stability a grounding electrode may add to it. If the GE is a metal water pipe and runs to other structures - it may very well carry all the neutral current and you never know you had a problem with service neutral.
 
kwired said:
With severing a neutral or feeder neutral you often won't have as extreme of voltage changes because of the higher chance of more balance on a service/feeder then on an individual MWBC. But that don't mean you can be assured of better balance either. I see this not only on three phase wye, but also single phase three wire. Someone loses main neutral and only has somewhat minor voltage issues, that is because of what load balance there is plus what stability a grounding electrode may add to it. If the GE is a metal water pipe and runs to other structures - it may very well carry all the neutral current and you never know you had a problem with service neutral.
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Maybe true for the electrical aspect of things, but, a worry free situation should not exclude the plumber who might open a union under a severed service neutral scenario.


JAP>
 
kwired said:
If the GE is a metal water pipe and runs to other structures - it may very well carry all the neutral current and you never know you had a problem with service neutral.
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Until a GEC connection is loosened for some reason. :rant:

jap said:
Maybe true for the electrical aspect of things, but, a worry free situation should not exclude the plumber who might open a union under a severed service neutral scenario.
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Which is why water meters require bypass jumpers.
 
jap said:
It's good to know that if a service neutral gets severed somehow that your neutral pulled for every branch circuit will somehow make for a worry free situation.


JAP>
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comparing the service neutral to the branch circuit neutrals is like comparing apples and oranges. If the service neutral is lost, there could be widespread damage within the residence or commercial building. It is far more likely that a branch circuit will be worked on than the main service or a feeder.
 
I just get so tired of hearing about all the epic damage a MWB circuit can cause.

Point is, a neutral is a neutral, and, the service to most every structure is a MWBC to begin with.

So actually the comparison is apples to apples.
I came up in the trade with some of the best electricians there were. We used MWBC's without giving it a second thought. Also used the conduit as the EGC with very little or no issues at all.

Most of the scary things you posted about idiots braking neutrals,burning things up, shoddy conduit installs where you feel like you have to pull a redundant EGC when there's actually not a better EGC are all indicative of one thing.

Poor craftsmanship.
Not code requirements.

JAP>
 
jap said:
I just get so tired of hearing about all the epic damage a MWB circuit can cause.

Point is, a neutral is a neutral, and, the service to most every structure is a MWBC to begin with.

So actually the comparison is apples to apples.
I came up in the trade with some of the best electricians there were. We used MWBC's without giving it a second thought. Also used the conduit as the EGC with very little or no issues at all.

Most of the scary things you posted about idiots braking neutrals,burning things up, shoddy conduit installs where you feel like you have to pull a redundant EGC when there's actually not a better EGC are all indicative of one thing.

Poor craftsmanship.
Not code requirements.

JAP>
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Thank you. I had a similar upbringing and am grateful for it.
 
ActionDave said:
Thank you. I had a similar upbringing and am grateful for it.
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consider yourselves both lucky then. perhaps I am too young, or have seen an inordinate amount of bad work.

Again, I mean no disrespect to the elegant multiwire branch circuit.

would you at least both agree that craftsmanship and training have declined in recent years?
 
JFletcher said:
would you at least both agree that craftsmanship and training have declined in recent years?
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yes, i would. i realize i was lucky to break in with a really great crew and then upgraded to something even better at my present job, but i was also curious and wanted to learn this trade as best i could.

thing is, i'm kinda funny about this craftsmanship thing because i hate to see money and materials wasted in the name of craftsmanship as much as i hate to see bad work.
 
JFletcher said:
comparing the service neutral to the branch circuit neutrals is like comparing apples and oranges. If the service neutral is lost, there could be widespread damage within the residence or commercial building. It is far more likely that a branch circuit will be worked on than the main service or a feeder.
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Intentionally working on the circuit is one thing, unintended opening of the neutral while in operation is another. with the handle tie rules in place those intentionally working on the circuit situations will decrease some- you still have old existing installs without the handle ties though. There is still quite a few failed neutrals on feeders/services happening out there as well as on MWBC's.

ActionDave said:
yes, i would. i realize i was lucky to break in with a really great crew and then upgraded to something even better at my present job, but i was also curious and wanted to learn this trade as best i could.

thing is, i'm kinda funny about this craftsmanship thing because i hate to see money and materials wasted in the name of craftsmanship as much as i hate to see bad work.
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Same here. I like to do "neat work" but at same time it seldom is "perfect" looking.
 
JFletcher said:
would you at least both agree that craftsmanship and training have declined in recent years?
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Generally, good electricians train good electricians who train good electricians.
Craftsmanship is usually something built into the person regardless of what they're doing.
Stand up companies still offer training.

I think what most may see as a decline in workmanship is actually due to some wanting to change gears in their trade such as going from residential to commercial and commercial to industrial for a bigger piece of the pie.

Most that have been brought up as a residential electrician don't know how to run pipe.
Those in the commercial field that may know how to run pipe may have never had to bend or threaded rigid and so on.

They can get there, but, generally what is looked upon as bad craftsmanship is either because they haven't gained enough experience as of yet, or, the complete opposite, they simply don't give a rip.

JAP>
 
jap said:
Most that have been brought up as a residential electrician don't know how to run pipe.
Those in the commercial field that may know how to run pipe may have never had to bend or threaded rigid and so on.
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The opposite is often true, too. I have seen commercial electricians who have no idea what to do with NM.
 
LarryFine said:
The opposite is often true, too. I have seen commercial electricians who have no idea what to do with NM.
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Yup. I hired a commercial guy once, never did residential. He was sooo slow.

Sent from my A574BL using Tapatalk
 
JFletcher said:
Commercial guys might do Residential here and there but most of them hate crawl spaces in attics I know I do LOL.
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I must get some of the wrong commercial places, been to many with crawl spaces. Though most of the newer places that isn't so common.
 
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