Multiwire Branch Circuits

[earshavewalls]

Now that Article 210.4(B) requires common-trip for all circuits sharing a neutral (see the definition of Multiwire Branch Circuit), has anyone else been seeing a lot of engineered plans with notes indicating that each circuit is to have its own neutral?

I think this is the laziest trend I have seen to date! I quote this Article on my plan checks where I see hash marks on the homerun arrows indicating the number and type of conductors to be used and remind them that they must provide multi-pole breakers or listed handle ties for these breakers. The next submittal, typically, has the hash marks removed and a note provided stating that dedicated neutral is to be used for all circuits.

This is just plain lazy! All it will take is a contractor trying to "value engineer" and use MWBC's to save on conductors, for the inspector to send them in for plan revisions. This way, the engineer may be justifying an extra charge, based on a field change made by the contractor.

It seems to me that in these economic times that people would be more fiscally responsible. I remember the days when engineers were hired to SAVE money on a project. Now, they are driving costs up just by being lazy.

I'm just venting, but this is frustrating to me to see customers paying a price for the laziness of the people they hire.

GRRRRRRRRR

Wayne

 

[Bryan Holland]

I agree.

I wonder if those same engineers and contractors realize that every service and feeder is a multiwire circuit. Whats the difference???

 

[north star]

* * * *

One difference is that not many people are educated enough to know the actual

requirements [ of the NEC ], and that laziness and things missed on the plans /

project means "directly realized profit".....Speaking for myself, ...trying to

continuously read & actually understand the NEC and apply it correctly, is

like trying to read, understand & apply "correctly", the Mandarin Chinese

language and baby talk combined! :banghd......I just ain't savvy enough to be able

perform this tasking!

* * * *

 

[GHRoberts]

The solution that the engineer chooses seems to be the correct solution. He has no control over how the multiwire circuits are connected to the panel. Either now or in the future if breakers are replaced. So he makes it right regardless.

 

[chris kennedy]

Now that Article 210.4(B) requires common-trip for all circuits sharing a neutral

Incorrect

they must provide multi-pole breakers or listed handle ties for these breakers.

Correct

has anyone else been seeing a lot of engineered plans with notes indicating that each circuit is to have its own neutral?

Not yet.

I think this is the laziest trend I have seen to date! I quote this Article on my plan checks where I see hash marks on the homerun arrows indicating the number and type of conductors to be used and remind them that they must provide multi-pole breakers or listed handle ties for these breakers. The next submittal, typically, has the hash marks removed and a note provided stating that dedicated neutral is to be used for all circuits.This is just plain lazy! All it will take is a contractor trying to "value engineer" and use MWBC's to save on conductors, for the inspector to send them in for plan revisions. This way, the engineer may be justifying an extra charge, based on a field change made by the contractor.

It seems to me that in these economic times that people would be more fiscally responsible. I remember the days when engineers were hired to SAVE money on a project. Now, they are driving costs up just by being lazy.

I'm just venting, but this is frustrating to me to see customers paying a price for the laziness of the people they hire.

GRRRRRRRRR

Wayne

Got your knickers in a twist there Wayne? From an installers point of view, the size of jobs I do always require as-builts. Therefore I make the call on MWBC's used. I had to correct you on the "common trip" stated due to costs involved. Three 20A bolt-ins cost my employer $45, handle ties $1. A 3 pole bolt-in runs $100.

I have no problem running MWBC's for lighting circuits due to the fact that if I have to shut down 3 circuits to work on one the EM lights will keep the disruption to a minimum. The problem I see here lies in running MWBC's to office rec circuits. If I turn off 3 to work on 1, how many computers am I taking out???

I'm no fan of the new 210.4(B) thinking that if I had to go in and work on one rec circuit I may be tempted to pull that conductor off the 3 pole/handle tied breaker hot. Bottom line is 210.4(B) has dumbed down the code for the protection of non-qualified personal.

 

[earshavewalls]

Yeah, this does have my knickers.......we all have the luxury of disagreeing with the code, but I happen to have the inglorious duty of enforcing the codes as they are written. I believe this code change was meant to provide a bit more protection for service personnel, not to make it easier to work on office electrical power while the office is in operation. Regardless of the reason for the change, this is the code and I must enforce it. Listed handle ties are approved for this use as are multiple-pole breakers, the cost is up to the designer. Here in California, we allow contractors to do "design/builds" but we also require that they provide plans that demonstrate a compliant design before we issue a permit. Part of that design is to determine where and how multiwire branch circuits will be utilized. The power distribution demonstrated on the power and lighting plans must agree with the panel schedules. This is in regards to the multiwire branch circuit issue as well as CEC 408.4 (distinguishing descriptions of circuits).

Since the 2005 NEC, it has been required to provide common-trip for multiwire branch circuits in fixed and moveable partitions (office partitions)......aren't these areas where most of the computers will be utilized? You need to shut down a group at a time of these cubicles since the MSBC's serving them are required to have simultaneous disconnection of all ungrounded conductors (Art. 605).

I used to do Electrical Project Management and Estimating and I would always produce "Value Engineering" options to our customers when bidding a project. One of these was to suggest methods that would take a little more "engineering time" to produce on the plans. We would re-route systems and come up with other "Real-world" solutions and cost savings. It bugs me that some of the engineers designing some of the projects I am reviewing simply added a note to the plans stating that dedicated neutrals are to be used........ONLY to be able to address my comment and to get their permit issued. Now, once the contractor comes in and sees that they can save some time by sharing neutrals in the home runs, they will need to resubmit the revisions to B&S for review before being issued a C of O. If this were done in the first place, there would be no need to delay the project at the end.

I'm just saying that there are a lot of people out there who make a lot of money for doing as little as possible rather than using the education that they spent much of their time and money to get to give their customer the most frugal design possible. Isn't that what we used to use engineers for? There was a time when engineers used to work hard at making their designs as efficient as possible. Now-a-days, you mostly just get something that will get past the plan checker, with no regard for the customer's real needs.

OK.......that's enough venting.........................I think I've said all I can on this subject. It still bugs me, but I know I'll get over it.........................especially after I keep hitting designers/engineers on this issue, over and over and over....................it's a never-ending job!!!

 

[Paul Sweet]

It may also have to do with harmonics. Once upon a time it was assumed that there was negligible current in neutrals. Now with the harmonics generated by switching power supplies in computers, etc. can cause the neutral to have a significant current.

Good engineering isn't only about saving money on first costs. With the churn rate in many offices, if multiple cubicles have to be shut down to make changes in one, the extra neutrals might offset the downtime. Also, I believe the internal wiring in many cubicles (at least the ones we had where I used to work) had separate neutrals for each circuit.

 

[earshavewalls]

I would be the first to agree that dedicated neutrals would be the way to go ALL of the time, for reasons of harmonic interference, voltage fluctuations, etc. A much more stable system could be built using dedicated neutrals AND grounds for each circuit..........but this would truly only benefit IT equipment more than anything else. The reality of installations, and particularly in the state the economy has been in for the past few years, is that costs are a HUGE consideration, especially on larger scale projects. I am just saying that when given the option of providing circuiting or simply adding a note to the plans, the engineers I have been dealing with usually just take 'easy street' right away and add a note to the plans for dedicated neutrals...........then they are done!

I just think that the owner or payee might want a say in this, but that is not what happens. I am just venting about what I see everyday.

 

[TJacobs]

Yeah, this does have my knickers.......we all have the luxury of disagreeing with the code, but I happen to have the inglorious duty of enforcing the codes as they are written. I believe this code change was meant to provide a bit more protection for service personnel, not to make it easier to work on office electrical power while the office is in operation. Regardless of the reason for the change, this is the code and I must enforce it. Listed handle ties are approved for this use as are multiple-pole breakers, the cost is up to the designer. Here in California, we allow contractors to do "design/builds" but we also require that they provide plans that demonstrate a compliant design before we issue a permit. Part of that design is to determine where and how multiwire branch circuits will be utilized. The power distribution demonstrated on the power and lighting plans must agree with the panel schedules. This is in regards to the multiwire branch circuit issue as well as CEC 408.4 (distinguishing descriptions of circuits). Since the 2005 NEC, it has been required to provide common-trip for multiwire branch circuits in fixed and moveable partitions (office partitions)......aren't these areas where most of the computers will be utilized? You need to shut down a group at a time of these cubicles since the MSBC's serving them are required to have simultaneous disconnection of all ungrounded conductors (Art. 605).

I used to do Electrical Project Management and Estimating and I would always produce "Value Engineering" options to our customers when bidding a project. One of these was to suggest methods that would take a little more "engineering time" to produce on the plans. We would re-route systems and come up with other "Real-world" solutions and cost savings. It bugs me that some of the engineers designing some of the projects I am reviewing simply added a note to the plans stating that dedicated neutrals are to be used........ONLY to be able to address my comment and to get their permit issued. Now, once the contractor comes in and sees that they can save some time by sharing neutrals in the home runs, they will need to resubmit the revisions to B&S for review before being issued a C of O. If this were done in the first place, there would be no need to delay the project at the end.

I'm just saying that there are a lot of people out there who make a lot of money for doing as little as possible rather than using the education that they spent much of their time and money to get to give their customer the most frugal design possible. Isn't that what we used to use engineers for? There was a time when engineers used to work hard at making their designs as efficient as possible. Now-a-days, you mostly just get something that will get past the plan checker, with no regard for the customer's real needs.

OK.......that's enough venting.........................I think I've said all I can on this subject. It still bugs me, but I know I'll get over it.........................especially after I keep hitting designers/engineers on this issue, over and over and over....................it's a never-ending job!!!

I say AMEN to the quote in bold.

 

[chris kennedy]

I would be the first to agree that dedicated neutrals would be the way to go ALL of the time, for reasons of harmonic interference, voltage fluctuations, etc. A much more stable system could be built using dedicated neutrals AND grounds for each circuit..........but this would truly only benefit IT equipment more than anything else.

How many grounded conductors are at the service and POCO transformer? One. One big multi wire circuit.

 

[GHRoberts]

I'm just saying that there are a lot of people out there who make a lot of money for doing as little as possible rather than using the education that they spent much of their time and money to get to give their customer the most frugal design possible. Isn't that what we used to use engineers for? There was a time when engineers used to work hard at making their designs as efficient as possible. Now-a-days, you mostly just get something that will get past the plan checker, with no regard for the customer's real needs.

Considering that engineers get paid for their time ...

Unless you are doing really big projects there is little cost advantage to doing much engineering.

In data centers you don't worry about the wiring --- you can save a lot more by specifying the right computer components. You do the engineering where there are opportunities to save or waste electric power.

 

[peach]

handle ties - see them all the time with disposals and dishwashers.... and system furniture

 

[RJJ]

Chris you make some great points!