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Joined: Oct 2000
Posts: 2,722
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Scott35 Offline OP
Broom Pusher and
Re: Article 210.4(B) - 2008 NEC;
Interpretation of Article -VS- "Intent" of the Article.

Looking for input from anyone in the Design / Applications / Management areas, and especially from Inspectors, Plans Examiners and Code Consultants, regarding the Long-Winded Post below!

On a very large, and very complex Project we have (out of State, not in California), the DBS (Building Department) just adopted the 2008 NEC.
Adopted in entirety, with no amendments, in effect September 1st, 2008.

I Designed / Engineered the areas within "Our Scope Of Work" (there are 3 other E.C.s on this Project - told you it is a big project!), and submitted the Plancheck Set in late August, 2008.
No P/C revisions were requested, nor were any Bulletins or other documents issued by the DBS.

Panelboards, Switchgear & Transformers were supplied and installed by another E.C. (panels, gear, transformers, devices and feeders not in our scope / N.I.C.).

In July, 2008, I submitted Panel Schedules describing the Circuitry + Devices we needed for our Scope, to the Electrical Consultants hired by the Client.
This Firm is to supply the Panels, Gear, Devices and Transformers to the installing E.C.(s) of the project.

Work began on the Project September 8th, 2008, and I am Project Manager for this job.

Now to the point!!!

The DBS is interpreting 210.4(B) to be for _ANY_ Multiwire Branch Circuit - not simply where a MWBC terminates to a single yoke, or in a single piece of Equipment.

Simply stated, all the Multi Wire Lighting Circuits I have Designed on this Project, will require Multipole Common Handle Tie Circuit Breakers, even though no single Fixture will have 2 or more Circuits terminating inside them.

I contacted the DBS to verify the interpretation, and they confirm the above interpretation.

Am I missing the point of the Article, or is this a mis-interpretation by the DBS?

As I understand (and interpret) Article 210.4(B), it's intent is to eliminate the hazard of One (or more) Ungrounded Conductors being left energized on:

* A Single Yoke Device - such as a Receptacle,
* In a single piece of Equipment - such as a Lighting Fixture, having Ballasts connected to 2 individual Circuits;
1 Ballast from switched Lighting Circuit on CKT #10, 1 Emergency Battery Back-Up Ballast connected to unswitched Lighting Circuit on CKT #12

If separate 1 pole devices were used for the above listed Circuits, a _QUALIFIED_ Person working on the Device / equipment may inadvertently leave one or more 1 pole OCPDs closed, for the MWBC feeding the item, introducing a Ground Fault hazard at the item.

Risk of L-G Ground Fault (shock, short circuit/sparks flying, or both) is dramatically reduced at the single device / equipment by the use of a Multipole or Common Handle-Tie OCPD.

This _DOES NOT_ include Junction Boxes with MWBCs, or multiple Outlets / Equipment where MWBCs will run through, but only a 2-wire Circuit (L-N) terminates on the device, or at the equipment.

This is really a problem for this particular project, as the Lighting Circuits use Lighting Contactor type Circuit Breakers (read: $$$).
Additionally, one of the Lighting Panels is connected via ATS to the Emergency Power System - and the Night Lights / Emergency Lights are derived from that Panel, along with several General Lighting Circuits for common areas.

The "Switched" Gen. Ltg. circuits from that Panel include an Unswitched circuit, for Night Lights / Emergency Lights in the common areas.
These are MWBCs.

A 3 Pole device with Lighting Control feature, will open the unswitched circuit, leaving the Em. lighting to run solely on Battery Back-Up power for > 8 hours.
This, of course, will drain the Batteries in less than 120 Minutes - every day, leaving the egress areas unlit.

Any comments???

Looking for input from anyone in the Design / Applications / Management areas, and especially from Inspectors, Plans Examiners and Code Consultants.

Thanks in advance.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
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Joined: Jul 2004
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If this was permitted under 2008 that is what it says.
They deleted the "single yoke" language.

Greg Fretwell
Joined: Jan 2005
Posts: 316
I am going to say you have to use common trip or approved handle tie's.
(Side note: don't overlook 210.4(D) grouping. )

Joined: Jan 2005
Posts: 5,411
Likes: 1
Cat Servant
The exact methods of making a multi-wire branch circuit have been the focus of many an internet debate. If you're a fan of scattering the 'legs' all over the panel, all I can say is, in the 2008, "you're busted!"

You have my sympathies. I consider this change to be one of the most far-reaching, profound changes in the 2008 cycle ... a 'stealthy' one that snuck in without anyone catching it. I'm also certain that the panels have received many proposals about it!

Simply put, ALL mwbc's need to be fed from a multi-pole breaker, and the wires need to be grouped / zip tied together in at least one point in the panel - including the neutral.

While I consider these practices to be very good practices, I cannot endorse making them mandatory. IMO, the NEC has crossed over into design issues.

Thank you for pointing out another problem with having the multiple circuits ALWAYS trip together. It certainly makes troubleshooting harder (which one of the three has the problem?), and can defeat the purpose of putting lights and receptacles on different circuits.

Joined: Oct 2006
Posts: 745
Well, I must say that I strongly disagree with this requirement unless a single yoke device is involved. We are supposed to be professionals. We all know that MWBC's must be kept on opposing phases. We know how to work safely with these circuits.

When does the NEC change from being a material of reference to a complete safety manual? There are always going to be idiots out there who don't know how to work safely with MWBC's, but why does the code have to be modified (at significant cost to EC's and their customers) to protect them? Every time someone causes a vehicle accident, the state doesn't rewrite the motor vehicle code do they?

How about AFCI's? Ballast disconnects? Tamper-proof receptacles? Don't get me started on those issues.

Back to the lighting MWBC issue: Look at the inconvenience that this requirement is going to cause a qualified service person. Now, to safely service a single fixture on a group of lighting circuits in an office, 3 times the number of people will be left in the dark. Seems pretty silly to me.

I'm all in favor of doing things safely, but at what point does the code become a guide to prevent unqualified people from hurting themselves? How far must it continue to go?

If you ask me, it's all about the wire manufacturers wanting us to buy more wire and the breaker manufacturers wanting us to buy more expensive 2 or 3 pole breakers. Good old NEC at work; business as usual.


"But the guy at Home Depot said it would work."
Joined: Jan 2005
Posts: 5,411
Likes: 1
Cat Servant
Ed, I feel your pain. BUT....

This code has been available for some time. The period to submit proposals for the next edition has just closed.

I can't speak for others ... but I got MY proposals in. Maybe the code panel will 'see the light' .... I am guessing that their chances of agreeing with me are closely influenced by how many others felt inclined to make proposals similar to mine.

Complaining after the fact makes it all the more difficult to get the panels to reverse their earlier decisions. I agree that this section snookered everyone .... let's hope the panel members are reading this thread.

Joined: Jan 2005
Posts: 354
pdh Offline
I take the position of agreeing with the 2008 code on this.

On the face of it, the primary hazard exists with line-to-line loads. You need a means to disconnect all ungrounded conductors into a load to avoid cross energizing. It might seem that line-to-neutral loads are safe in this regard.

However, maintenance of (parts of) a MWBC could involve disconnecting the grounded conductor. In the case of single phase 3-wire, this can result in a hot neutral. In the case of three phase 4-wire, this could create the additional hazard of voltage instability between equipment on the other still-connected phases. Note that this rule applies to the means of disconnect, not the OCPD. It's the disconnect that applies when maintenance is in progress.

I'm sure no one here would ever do such work without disconnecting all the phases, especially if the work might need to break the neutral during progress. But are all the phases even going to be next to each other when single pole breakers are used (on a panel you didn't wire up)? Requiring a common disconnect ensures a grouped disconnect. It also ensures a condition safe for maintenance being applied to the ungrounded conductor (or any conductor).

Joined: Jul 2004
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Likes: 25
I'm sure no one here would ever do such work without disconnecting all the phases, especially if the work might need to break the neutral during progress

I suppose the question would be, how do you know you are working on a MWBC if the breakers and conductors are not grouped and handle tied?
This is not usually a problem when everything is fresh but after years of alterations and additions you might "lose" that identification.

Greg Fretwell
Joined: Jan 2005
Posts: 5,411
Likes: 1
Cat Servant
I've long been an advocate of finding some way to identify neutrals. I've tried several schemes, but all have had extremely limited utility.

If I can plan the job from the start, many possible sources of confusion can be avoided.

Naturally, several remodels / repairs / modifications later, and all bets are off.

Yet, even the new code provisions will not help, in that I have found multiple 'round robins' tied into the neutrals. This usually happens in a junction box, where the neutrals either get confused, or, more common, they all get landed under a single wire nut.

What we really need is another color for neutral wires!

Yet, all my methods are but 'trade practice.' Useful as they are, I cannot imagine making them a matter of code.

I get the feeling that the code panel has developed a bias against the very use of MWBC's, but has not found the courage to actually come out and say so. I can imagine the arguments; from an academic perspective, it's all too easy to make the case against their use.

Yet, these Ivory-tower arguments all pale in the tangle of a crowded junction box, a cluttered panel, and the difficulty of pulling in that additional wire.

These are some of the reasons I consider this code rule to be 'bad law,' and would like to see it removed.

The 2008 edition of the NEC was pretty profound in the scope of it's changes. We were all so busy discussing AFCI's, then tamper resistant, that some major changes (like this one) got missed until it was too late.

IMO, whether or not to use MWBC's, and how to do them, are design issues, and ought to be left out of the NEC.

Joined: Jul 2004
Posts: 9,869
Likes: 25
This is just another reason I would like to see the NEC on a 5 year, or maybe even 10 year cycle. The TAC could deal with truly bad stuff that slips through but it would be less likely to happen if the cycle was long enough to really analyze changes for a while before you print them and let the current code settle a bit before you change it again. If we were just putting the finishing touches on the 1999 code changes for a 2009 release we would actually have AFCIs that work before we jammed them down people's throats and we would have had time to discuss things like this MWBC thing.
Nobody ever said you couldn't install any listed item like a TR receptacle or an AFCI as soon as it was listed. Leave it up to the manufacturers to sell them to the public. If the public really is convinced this is a good idea we will be happy to put them in.
Could you sell them? Sure, this is the public that buys "green plugs", electronic varmint repellers and "baby on board" signs.

Greg Fretwell
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