I had a question on multi-wire branch circuits and neutral or the (usually) white, grounded wire. Are there any occasions in a standard 120 volt circuit when you have to change the size of the grounded wire due to the size or type of load? Would one ever use a multi-wire branch circuit with a non-linear load? I have searched my code book and all other references I have.
Neutral sizing in residences
- Thread starter rjlight
- Start date
- Status
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Neutral sizing in residences
It seems to me that in a residential situation this kind of concern is not likely to be much of an issue. But maybe I am in error on this point.
I am not a huge fan of multiwire circuits, just because they introduce some less than obvious factors into troubleshooting and would never allow them in an industrial setting on any of my projects, although I'd be willing to bet a few have been snuck in on me here and there. EC's are pretty good at shaving a few bucks here and there, and they are not always totally scrupulous at following the drawings. You know how it is, "them college boys don't know nothing...".
They do reduce costs however, and that is an especially important factor in home construction. They are also perfectly safe when done correctly.
It seems to me that in a residential situation this kind of concern is not likely to be much of an issue. But maybe I am in error on this point.
I am not a huge fan of multiwire circuits, just because they introduce some less than obvious factors into troubleshooting and would never allow them in an industrial setting on any of my projects, although I'd be willing to bet a few have been snuck in on me here and there. EC's are pretty good at shaving a few bucks here and there, and they are not always totally scrupulous at following the drawings. You know how it is, "them college boys don't know nothing...".
They do reduce costs however, and that is an especially important factor in home construction. They are also perfectly safe when done correctly.
- Location
- Massachusetts
Re: Neutral sizing in residences
I spend a lot of my time in large retail and office space where branch circuit run lengths of 200', 300', 400' are the norm. In this work the use of multiwire branch circuits is a big help on cost and voltage drop issues.
I am not 'cheating or unscrupulous' the drawings will show multiwire branch circuits.
The added complexity is minimal and any electrician working in these buildings should be able to deal with it.
I get the feeling you do not think much of electricians?
I have not done much industrial work, I imagine that there are panels located close by so the run length of these two wire branch circuits are fairly short. The avoidance of down time is probably concern number one. In those settings it would seem cost effective to use all two wire circuits.
I spend a lot of my time in large retail and office space where branch circuit run lengths of 200', 300', 400' are the norm. In this work the use of multiwire branch circuits is a big help on cost and voltage drop issues.
I am not 'cheating or unscrupulous' the drawings will show multiwire branch circuits.
The added complexity is minimal and any electrician working in these buildings should be able to deal with it.
I get the feeling you do not think much of electricians?
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: Neutral sizing in residences
I do a lot of both commercial and industrial design, and I don't hesitate to use multi-wire branch circuits. In industrial, they are usually limited to convenience receptacles, single phase circuits not dedicated to machinery, etc. In commercial, I use them throughout, and really don't understand why not. As Bob indicated, voltage drop is cut in half, there are fewer current carrying conductors, and the client gets a good job for less money. I know of no advantage to running individual circuits in commercial installations that would overcome the benefits of multi-wire circuits.
Jim T
I do a lot of both commercial and industrial design, and I don't hesitate to use multi-wire branch circuits. In industrial, they are usually limited to convenience receptacles, single phase circuits not dedicated to machinery, etc. In commercial, I use them throughout, and really don't understand why not. As Bob indicated, voltage drop is cut in half, there are fewer current carrying conductors, and the client gets a good job for less money. I know of no advantage to running individual circuits in commercial installations that would overcome the benefits of multi-wire circuits.
Jim T
Ed MacLaren
Senior Member
Re: Neutral sizing in residences
Wouldn't that be the only types of loads for which the multi-wire circuit would be applicable?
Just nit-picking.
Ed
[ February 08, 2005, 08:57 AM: Message edited by: Ed MacLaren ]
I'm wondering what would be the difference, in terms of downtime, between one four-wire circuit and three two-wire circuits, for lighting or receptacle circuits in an industrial facility?
Wouldn't that be the only types of loads for which the multi-wire circuit would be applicable?
Just nit-picking.
Ed
[ February 08, 2005, 08:57 AM: Message edited by: Ed MacLaren ]
- Location
- Massachusetts
Re: Neutral sizing in residences
Originally posted by Ed MacLaren:
Just nit-picking.
Having 277 volt lighting on MWBC can lead to some trouble when working on the circuit, you may end up needing to turn off all 3 circuits which puts a big area in the dark.
I am looking forward to the new rule that requires a disconnect at the fixtures (factory installed) for servicing.
Ed MacLaren
Senior Member
Re: Neutral sizing in residences
Ed
[ February 08, 2005, 09:32 AM: Message edited by: Ed MacLaren ]
Edit - Re-read your post, (we said the same thing.)
Ed
[ February 08, 2005, 09:32 AM: Message edited by: Ed MacLaren ]
- Location
- Illinois
- Occupation
- retired electrician
Re: Neutral sizing in residences
Don
When using multiwire circuits on single phase systems there are no grounded conductor problems caused by non-linear loads. These problems only occur in three phase systems.
Don
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Neutral sizing in residences
Originally posted by iwire:
I actually think quite highly of electricians in general. Most are pretty good at what they do. I don't object to ECs who follow the drawings. I do object to those who will cut whatever corner they can in the hopes I won't notice. Generally these guys are not so common anymore. But I have had my fill of them.I am not 'cheating or unscrupulous' the drawings will show multiwire branch circuits.
The added complexity is minimal and any electrician working in these buildings should be able to deal with it.
I get the feeling you do not think much of electricians?
Plant maint people and instrument techs sometimes have a problem with multiwire circuits. They understand they work, but troubleshooting them is a little different. I don't care if the EC's electrians can troubleshoot them or not. The EC leaves at some point and the people in the plant have to take care of the equipment.
What I care about most is getting the thing up and running. When it can cost 10 grand a day (or more) for every day something is sitting waiting for it to start up, its hard to argue that the extra $20 to pull another wire is not worth it.
Most of the time I only have a very few 120V power circuits so cost is not a big issue. In fact, generally we have a control transformer so we can make out own right inside our panels, so it gets done the way I want it, and there is not an issue at all.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Neutral sizing in residences
If they don't know how a MWBC works, call a pro.
I've worked in production, performed maintenance tasks. It was pretty well understood that any work that required an electrical license shouldn't be taken lightly. We'd replace motors for the conveyor, and replace cord ends, etc. But beyond that, the people at the plant should call an electrician. There's some serious liability issues if a fellow employee gets shocked from an employee's error, especially if that employee's boss told him to do the work.
If they don't know how a MWBC works, call a pro.
Re: Neutral sizing in residences
I must say, IMO this thread has been one of the best threads ever thanks to Iwire. We now have a great shortcut for Multi-wire Branch Circuit, (MWBC) and for that I'm gratefull.
BTW, if anyone can not recognize a MWBC, they would have no business having their paws in the wiring in the first place.
Roger
[ February 08, 2005, 07:43 PM: Message edited by: roger ]
I must say, IMO this thread has been one of the best threads ever thanks to Iwire. We now have a great shortcut for Multi-wire Branch Circuit, (MWBC) and for that I'm gratefull.
BTW, if anyone can not recognize a MWBC, they would have no business having their paws in the wiring in the first place.
Roger
[ February 08, 2005, 07:43 PM: Message edited by: roger ]
- Location
- Massachusetts
Re: Neutral sizing in residences
LMAO
OK thats it, I am done now, the computer is getting thrown out and I am heading to the monastery.
Bob
LMAO OK thats it, I am done now, the computer is getting thrown out and I am heading to the monastery.
Bob
Re: Neutral sizing in residences
Savings of a multiwire is more than 1 more wire or 3 ph 2 wires. Each box has more wires. If you had a 3 ph multi network spliced in a box going to 3 pipes it would be 9 wires. With seperate nuts it would be 18 wires in one box. the box needs to be bigger. More labor splicing and cramming wires in a box. More labor pulling wires cause less wires is easier to pull. More to keep track of what nut. goes with what. Then you have conduit capacity. May need bigger pipes or more of them.
If someone can't figure out a multi wire circuit haw are they going to know what nutral to use if you have a hand full of differnt ones?
If you want it more full proof you should get a dedicated pipe for each circuit. Then you only have a hot and nut to get backwards. That's only more wires, more pipe, connectors, couplers, straps, labor, and $$$.
Multi Tom
Savings of a multiwire is more than 1 more wire or 3 ph 2 wires. Each box has more wires. If you had a 3 ph multi network spliced in a box going to 3 pipes it would be 9 wires. With seperate nuts it would be 18 wires in one box. the box needs to be bigger. More labor splicing and cramming wires in a box. More labor pulling wires cause less wires is easier to pull. More to keep track of what nut. goes with what. Then you have conduit capacity. May need bigger pipes or more of them.
If someone can't figure out a multi wire circuit haw are they going to know what nutral to use if you have a hand full of differnt ones?
If you want it more full proof you should get a dedicated pipe for each circuit. Then you only have a hot and nut to get backwards. That's only more wires, more pipe, connectors, couplers, straps, labor, and $$$.
Multi Tom
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Neutral sizing in residences
Yeah, that felt good. MWBC. Very cool. Hail Badger!
Yeah, that felt good. MWBC. Very cool. Hail Badger!
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Neutral sizing in residences
My guess:
Neutral amps = Phase A - Phase B
Voltage Drop = 2KID/cm
The "2" represents 2 conductors (hence twice the distance), a hot and a neutral.
The amps ("I") on the neutral would go down, since neutral amps single phase = A-B. A reduction in "I" would lower the voltage drop.
Just a total stab in the dark. But I'm feeling close.
My guess:
Neutral amps = Phase A - Phase B
Voltage Drop = 2KID/cm
The "2" represents 2 conductors (hence twice the distance), a hot and a neutral.
The amps ("I") on the neutral would go down, since neutral amps single phase = A-B. A reduction in "I" would lower the voltage drop.
Just a total stab in the dark. But I'm feeling close.
- Status