Inspecting multiwire circuits in the panel

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ryan_618 said:
That is how the theory is supposed to work...
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If it doesn't work that way, I'll bet that more times than not, all of the panels handle ties disappear right after the the first time one of those breakers trip and take out 2 or 3 circuits
 
Now after reading all the replies wow..... I can see both the pros and the cons of the situation with MWBC's. I personally do not install MWBC and after I explain the extra up front costs versus the down the road costs I am told thank you. I think MWBC were designed to save money on circuits that have small to no load on the neutral. The modern day lighting loads are increasing in neutral loads. When a small expansion takes place all new pipe and circuits are now needed. That is great for you the contractor but costly to your customer. Long time customers are like friends and very good for business. So I feel (IMHO) that MWBC are only cost effective in areas that will never change. Unqualified maintenance personnel and home owners are not very knowledgeable on MWBC and the down side has more consequences than the up side.
 
cschmid said:
I think MWBC were designed to save money on circuits that have small to no load on the neutral. The modern day lighting loads are increasing in neutral loads.
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I have no idea what you mean, please explain. :smile:


When a small expansion takes place all new pipe and circuits are now needed.
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Again I don't know what you mean.

MWBCs reduce the number and size of the conduits needed.

Unqualified maintenance personnel and home owners are not very knowledgeable on MWBC
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Well we kind of agree here, the difference is I have no sympathy for those that do not understand what they have chosen to work on.

the down side has more consequences than the up side.
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I don't see any 'down' side.
 
dnem said:
I'll bet that more times than not, all of the panels handle ties disappear right after the the first time one of those breakers trip and take out 2 or 3 circuits
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Who is removing handle ties?

I have been at this 25 years and I can't recall finding removed handle ties or ever considering removing existing handle ties.
 
The only downside that I see is that there will be more pressure to do live work. Instead of turning off 1 circuit you may have to cut off 2 or 3. Especially in businesses.

The upside to that is the neutral shouldn't have voltage on it.
 
ties

ties

iwire said:
Who is removing handle ties?

I have been at this 25 years and I can't recall finding removed handle ties or ever considering removing existing handle ties.
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I have a decade or two on you, Bob, and I agree. I have rarely seen the ties removed, and in those few cases, that was the least of the electrical problems.
 
Cschmid, MWBC's saves natural resources, reduces voltage drop, reduces wattage used, reduce labor, to name a few positives

Barring additive harmonics, the grounded conductor in a MWBC where it is a neutral will never see more current than it would in a two wire circuit where it is not a neutral, meaning, a light load verses a heavy load has no bearing on it.

The truth is, the pay back from a MWBC will be long term to the user.

Roger
 
SmithBuilt said:
How does it do those things?
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Along with 480sparky's link, looking at the the natural resource savings is the metal for the conductors and conduit, fuel for generating electricity, etc... the labor aspect is obvious.

Roger
 
Here is an illustration from Ed MacLarren that will help visualisation.

Ed's3wireverses2wire.gif


Roger
 
Bob I was referring to the math provided by roger I just did not do as good as job as roger did.....

I too agree I have been in the business for almost 30 years and have never seen handle ties removed....

Al-thought I have seen MWBC with only single breakers and also have seen them sorted to be on the same phase so no handle tie could be used...

One of the reasons I feel that money is saved on not installing MWBC is that I can stagger the lighting schemes and work on de-energized circuits during regular hours and not shut down the business...

I do not install maxed out piping I have room to spare for expansion what is the difference between hundred feet of 3/4" vs 1/2" installation cost are the same except when we go to expand we save owner cash no need to run a bunch of extra pipe.

The benefits of not using MWBC in commercial and industrial out way the cash benefit of installing up front. when you count extra cost for off hour work and lost production when A ballast shorts out and shuts down a line because you lost two or three banks of lights instead of one. We do not have to work live circuits and do not have to do work after business hours this saves us money and our client money.

We can not idiot proof the world but I know unqualified people are going to do electrical work and I do care they have families too. I don't agree that they do the work but I can not stop them. We live in the same community, we know these people outside of work and our kids might of played together they might even be married to someone I know. WE do care it is our community together we make it work.
 
cschmid said:
Al-thought and also have seen them sorted to be on the same phase so no handle tie could be used...
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This would not be a MWBC

cschmid said:
One of the reasons I feel that money is saved on not installing MWBC is that I can stagger the lighting schemes and work on de-energized circuits during regular hours and not shut down the business...
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Why would this be different in present code using an MWBC? After it splits it is just two wire circuitry.

cschmid said:
I do not install maxed out piping I have room to spare for expansion what is the difference between hundred feet of 3/4" vs 1/2" installation cost are the same except when we go to expand we save owner cash no need to run a bunch of extra pipe.
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A hundred feet may not be much, 100,000 feet would be and nation wide it would be a lot more than that.

cschmid said:
The benefits of not using MWBC in commercial and industrial out way the cash benefit of installing up front. when you count extra cost for off hour work and lost production when A ballast shorts out and shuts down a line because you lost two or three banks of lights instead of one. We do not have to work live circuits and do not have to do work after business hours this saves us money and our client money.
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This doesn't make sense. Why would more than one breaker be affected?

cschmid said:
We can not idiot proof the world but I know unqualified people are going to do electrical work and I do care they have families too. I don't agree that they do the work but I can not stop them. We live in the same community, we know these people outside of work and our kids might of played together they might even be married to someone I know. WE do care it is our community together we make it work.
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Sorry, this is not my concern.

Roger
 
cschmid said:
The benefits of not using MWBC in commercial and industrial out way the cash benefit of installing up front. when you count extra cost for off hour work and lost production when A ballast shorts out and shuts down a line because you lost two or three banks of lights instead of one. We do not have to work live circuits and do not have to do work after business hours this saves us money and our client money.
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I'm curious as to why you would think that a MWBC would have any affect on your scenario? You simply de-energize the circuit feeding that ballast and change it. The fact that the fixture is fed from a MWBC is not relevant. Are you refering to using a handle tie?
 
SmithBuilt said:
In diagram B why would current that has gone thru load #1 then go thru load 2 and not take the easier path of the neutral wire?
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I think the way the arrows are drawn isn't quite right, IMO. I think of it as two hots feeding in, and the neutral returning the unbalanced portion. Ed's drawing may be correct and I'm off base, but I can't understand the arrows as drawn.

One thing that is for sure though, is if the load on phase A is 60, and phase B is 40, then 20 amps will flow on the neutral in a single-phase 120/240 system.

My rationalization for this is that the system is truly a 240V system. 40 amps are very happy travelling directly from A to B (and B to A) without looking at the neutral, because it's inherently a 240V system.

In the picture in my mind, I see the current that's flowing from A to the neutral as taking the neutral to get back to the B phase. The windings of the transformer between the neutral and the B phase have a higher resistance than the 40 amps is forced to take back to the B leg.

This may be way off, it's just the way my mind pictures the electrons flowing. :)

Edit to add: Well, it looks like I have a good thread to link to from the FAQ on this. ;)
 
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SmithBuilt said:
In diagram B why would current that has gone thru load #1 then go thru load 2 and not take the easier path of the neutral wire?
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Why do you think the neutral is the easier path? If both loads are equal to the center of the circuit the neutral can be removed not affecting either load, the circuit will simply be a 240 volt series circuit.

As far as the arrows simulating curent flow, just alternate them 60 times a second.

Roger
 
iwire said:
Who is removing handle ties?

I have been at this 25 years and I can't recall finding removed handle ties or ever considering removing existing handle ties.
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SmithBuilt said:
The only downside that I see is that there will be more pressure to do live work. Instead of turning off 1 circuit you may have to cut off 2 or 3. Especially in businesses.

The upside to that is the neutral shouldn't have voltage on it.
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If there?s pressure to work live because they don't want more than one circuit of lights off at a time then either take the handle ties off during the time you?re working on the circuits or say ?no? and don?t agree to work it hot. . And if you reinstall the handle ties after you?re done, then Bob can also work in your area without jeopardizing his 25 year streak.

augie47 said:
I have a decade or two on you, Bob, and I agree. I have rarely seen the ties removed, and in those few cases, that was the least of the electrical problems.
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If we now have to handle tie MWBCs, even when they don?t supply more than one circuit per receptacle yoke, I don?t see that as an electrical problem. . I see it as a potential code requirement but I don?t see it as a safety hazard or a problem. . At least not a hazard for a real electrician.

The code panel must be viewing it as a safety hazard for untrained workers but I see it as a government abdication of responsibility. . In Ohio, hairstylists have to be licensed but not electricians. . I see an abdication of oversight and regulation that can?t be solved by a new misguided unnecessary code rule.

cschmid said:
We can not idiot proof the world but I know unqualified people are going to do electrical work and I do care they have families too. I don't agree that they do the work but I can not stop them. We live in the same community, we know these people outside of work and our kids might of played together they might even be married to someone I know. WE do care it is our community together we make it work.
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The best thing you can do for those people is push your state legislator to license electricians and require good quality mandatory continuing ed for all of them. . Sometimes you have to protect people from themselves.

David
 
dnem said:
I see it as a potential code requirement but I don?t see it as a safety hazard or a problem. . At least not a hazard for a real electrician.

The code panel must be viewing it as a safety hazard for untrained workers but I see it as a government abdication of responsibility.
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David I agree with your thoughts but it is odd (at least to me) that one of the groups pushing for this handle tie requirement was the IBEW.

It seems to me they sell themselves on being better trained but at the same time want to 'dumb things down'
 
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