Circuit Wiring Concepts Questions

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jsun9

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Hey I am working as a building MEP electrical designer/engineer for almost a year, but there are a couple of terms that confused me so hard. Please help me out on this.

1） What are the relations and differences between multi-wire circuits, shared neutral circuits, and daisy chain circuits with regard to a 120V single phase power supply?

2）See image below. On wiring side, what are the differences if the receptacles are powered in such two ways?
IMG_8459.jpg
 
There is no difference between the two drawings. In one drawing you fed a jb and then fed each receptacle. In the other drawing it is what we call a daisy chain- from one to the next.

a multiwire branch circuit is one in which you share the neutral with 2 circuits that are on opposite phases. The load on the neutral is the difference between the phase load. If one phase of the multiwire branch circuit has 10 amps and the other has 15 amps then the neutral only sees 5 amps. If the load were on the same phase then the neutral load would be cumulative--0 25 amps in the example above
 
Dennis Alwon said:
There is no difference between the two drawings. In one drawing you fed a jb and then fed each receptacle. In the other drawing it is what we call a daisy chain- from one to the next.

a multiwire branch circuit is one in which you share the neutral with 2 circuits that are on opposite phases. The load on the neutral is the difference between the phase load. If one phase of the multiwire branch circuit has 10 amps and the other has 15 amps then the neutral only sees 5 amps. If the load were on the same phase then the neutral load would be cumulative--0 25 amps in the example above
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Hi Dennis, thanks for you quick reply. Let me think a little bit about your reply.
 
I wouldn't say there is no difference. Both situations you still get nominal 120 volts at each receptacle.

For short runs there is probably no significant differences when it comes to performance.

For long runs - if you "daisy chain" like in the second drawing you may experience more significant voltage drop at the end of the run then if you ran individual conductors to each outlet from a central point. Whether or not it is significant enough to offset the cost of extra conductor used is also a consideration.
 
Almost every circuit is wired daisy-chained, which is why receptacles have two terminals per side, unless there's a reason to have only one cable or conduit per box, like remodels or small boxes.
 
Your E supervisors have not served you well in your training, unless they only are hoping for a drafter that can loop circles and squares together and end with a homerun.

You must learn to visualize what you are asking an EC to install. Start looking for YouTube videos on different electrical circuit topics and insist on some support from the boss.
 
To expand on what Dennis states his response holds true for a 1Ø, 120/240 volt system or that portion of a 4 wire Delta system. If you had two circuits from the typical commercial 208Y/120 WYE system the neutral current may not cancel as in the 120/240 volt system. If you had a 2 circuit MWBC with 10 amps on one phase and 10 amps on the other the neutral would also carry about 10 amps.
 
MyCleveland said:
Your E supervisors have not served you well in your training, unless they only are hoping for a drafter that can loop circles and squares together and end with a homerun.

You must learn to visualize what you are asking an EC to install. Start looking for YouTube videos on different electrical circuit topics and insist on some support from the boss.
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Hey, I think you get the point, thank you so much for the advice.
 
Adder note that "daisy chained" is the one term that is really a valid one, and it is also one that I have never seen as a specified requirement applied to power and lighting wiring. It is more common in fire alarm and various control communications circuits like RS485, etc. But the accurate term for this is tandem wiring. The term I hear most often used in my area is "series" and I will correct people all the time because that DOES mean something and it is false. The devices are still wired in parallel, they are just wired "in-line" or in tandem.
 
Strathead said:
Adder note that "daisy chained" is the one term that is really a valid one, and it is also one that I have never seen as a specified requirement applied to power and lighting wiring. It is more common in fire alarm and various control communications circuits like RS485, etc. But the accurate term for this is tandem wiring. The term I hear most often used in my area is "series" and I will correct people all the time because that DOES mean something and it is false. The devices are still wired in parallel, they are just wired "in-line" or in tandem.
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Electrically loads still get connected parallel to the source.

The "one line" diagram shows a series or a chain from one component to the next, but that chain is multiple conductors in each link.
 
Welcome to The Forum.

The first picture is what is known in the data world as "star topography". I informally call it a spider design. It's common in old houses, trailers (mobile homes), and very long runs of landscaping lighting, tho I would say it is fairly uncommon in new commercial applications, except where Larry Fine mentioned.

Multiwire and shared neutral essentially mean the same thing.
 
The YouTube idea is good however I would not look at anything of a how to Nature as definitive or even correct... even some manufacturer videos are horribly incorrect. Most of them should be titled "how to kill yourself or burn down your house in 5 minutes".
 
LarryFine said:
Almost every circuit is wired daisy-chained, which is why receptacles have two terminals per side, unless there's a reason to have only one cable or conduit per box, like remodels or small boxes.
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For residential I would agree that most receptacle circuits are daisy chained.

When it comes to commercial wiring I think it normally comes down to what is the most practical, it may be easier to set a junction box in the ceiling(drop ceiling) and run individual MC cable or conduit to each receptacle.


When it comes to lighting circuits it's very common in commercial to see a junction box set at a central location and feed say four light fixtures.
 
Another difference between the two methods (spider-web v. daisy-chained) is when it comes to trouble-shooting. Daisy-chained can be easier to locate a fault. If the issue is in the j-box of the spider-web method, it can be difficult to locate and/or access the j-box. It might be in that ceiling fan that's up there in the 16' ceiling. I might be buried under the insulation up in the attic. It might be in a switch box. It might even be an open splice hidden in the wall behind a kitchen cabinet.
 
Dennis Alwon said:
There is no difference between the two drawings. In one drawing you fed a jb and then fed each receptacle. In the other drawing it is what we call a daisy chain- from one to the next.
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I would consider that a difference. A spur as opposed to radial.
Just my two pence worth.
 
Both of those drawings are functionally the same - parallel, 120v circuits. In the first diagram, the hot and neutral conductors feeding the outlets will be spliced with the hot and neutrals of the home run wire entering the jb. In the second diagram, the splicing happens within the outlet boxes.
 
jselesk2 said:
Both of those drawings are functionally the same - parallel, 120v circuits. In the first diagram, the hot and neutral conductors feeding the outlets will be spliced with the hot and neutrals of the home run wire entering the jb. In the second diagram, the splicing happens within the outlet boxes.
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Functionally same meaning each load is parallel to the source.

Depending on locations, distances, size or type of conductors, etc. you could see differences in voltage drop at the load(s).
 
jsun9 said:
Hey I am working as a building MEP electrical designer/engineer for almost a year, but there are a couple of terms that confused me so hard. Please help me out on this.

1） What are the relations and differences between multi-wire circuits, shared neutral circuits, and daisy chain circuits with regard to a 120V single phase power supply?

2）See image below. On wiring side, what are the differences if the receptacles are powered in such two ways?
View attachment 20082
Click to expand...
The information in the image is not information I want to see on any design drawing. The conduit routing should be left up to the installing electrical contractor. There is no way that the engineer/designer can know what the best routing will be for those small conduits at the time of the design. Electrically the accomplish the same thing...that is supply 120 volt single phase power to each of the receptacles.
 
don_resqcapt19 said:
The information in the image is not information I want to see on any design drawing. The conduit routing should be left up to the installing electrical contractor. There is no way that the engineer/designer can know what the best routing will be for those small conduits at the time of the design. Electrically the accomplish the same thing...that is supply 120 volt single phase power to each of the receptacles.
Click to expand...

I was going to tell him he would see it on the as-builts, but didn't want to get him too confused on what really happens in the field.
 
don_resqcapt19 said:
The information in the image is not information I want to see on any design drawing. The conduit routing should be left up to the installing electrical contractor. There is no way that the engineer/designer can know what the best routing will be for those small conduits at the time of the design. Electrically the accomplish the same thing...that is supply 120 volt single phase power to each of the receptacles.
Click to expand...
Can depend on some circumstances though. If the "daisy chain" results in long run and too much voltage drop by the time you reach the end, maybe designer does specify the "star" method or increased conductor sizes to meet the needs.
 
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