Bob Badger

I was forced to use EMT ...........

InPhase277

You guys must be coming back from church, and all uptight and serious this morning

Of course I was being a smart mouth. I was pointing out the stupid idea that MWBCs are safer on multi-pole breakers, or breakers with handle ties. If that is the case, then it is in the same vein that no box or pipe should have more than one circuit.

Sure there are inherent dangerous possibilities with open neutrals for an MWBC. But this is of no consequence for real electricians. Therefore, the handle tie rule of the '08 Code is pretty dumb and only inconveniences us. Now to turn a circuit off, we have to turn of at least one other circuit, which may be inuse at the time. Pipe fill goes up geometrically if we want to avoid that and use single poles. Etc.

The code making panels are attempting to idiot proof the code. That isn't the answer. Somehow, we need to idiot proof the trade.

Magnettica

I strongly disagree.

90.1 Purpose.

(A) Practical Safeguarding. The purpose of this Code is
the practical safeguarding of persons and property from
hazards arising from the use of electricity.

Bob Badger

I think the new rule will lead to more hot work being done, not less.

Peter D

Either that, or removal of the multipole devices after the fact.

perryx5

I agree that the code is trying to compensate for more unskilled laborers in the workforce. If we properly train the electrician labor force and keep unskilled people from going to Home Depot and listening to a 30 minute "seminar" and deciding to make some "improvements" to their electrical system, we do not need to protect said unskilled individuals from open neutrals. Within the first week of my apprenticeship the dangers of open neutrals were explained to me and at that time, with that level of experience, I knew I had no business working circuits hot. In the IBEW, apprentices are not supposed to work hot circuits until their second year, and even then, under the supervision of a JW. Not that everyone abides by this rule, but a good JW will know when an apprentice has grasped the concept of open neutrals enough to work circuits hot. I'm not trying to demonize Home Depot, but I have heard some of their electrical department personnel giving some downright dangerous advice to unskilled people before.

Jeremy

Minuteman

Another issue beside the danger to personnel is danger to equipment and property. If a neutral is opened in a energized MWBC, the result could be excessive voltage across the circuit. The magic smoke will leak out.

__________________
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"The Few, the Proud, the Infidel."
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Greg

After reading that article several times my question is this; Does the NEC want handle ties or multi-pole breakers? Is the intent to open all poles on a fault or open all pole when turning the circuit off. I realize when you reset the breaker you open all poles first but what does the NEC exactly want.

When they say open all ungrounded conductors simultaneously does that mean on a circuit fault or normal operation?

__________________
If you're gonna be stupid, you better be tough.

Dennis Alwon

I believe the intent is to open all poles when the circuit needs to be serviced and not on a fault.

Bob Badger

Jeremy, that is all very interesting guess work but the IBEW was one of the supporters of this change due to 'skilled individuals' being electrocuted on the job.

480sparky

Both a multi-pole breaker and a handle tie will satisfy the NEC.

A multi-pole breaker will turn off all poles when there's a fault in just one. A handle-tie doesn't (or at least shouldn't).

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jfwfmt

The choice of a breaker with simultaneous trip for all poles and for more than one breaker with independent trip and with handle ties is more subtle:

240.15 (B) (1) Multiwire Branch Circuit. Except where limited by 210.4(B), individual single-pole circuit breakers, with or without identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.

This seems to allow single breakers with no handle ties, BUT the reference to 210.4(B) essentially takes that away.

210.4(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

Handle ties suffice for 210.4(B)

210.4(C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.

This prohibits line-to-line loads on MWBC EXCEPT:

210.4(C) Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.

MWBCs are allowed to a single piece of equipment (like a heater with heating elements on line-to-line and fan on line-to-neutral)

210.4(C) Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

If you want to supply line-to-line load(s) you can do it, if you have SIMULTANEOUS trip on all poles. Handle ties do not suffice.

210.7(B) Multiple Branch Circuits. Where two or more branch circuits supply devices or equipment on the same yoke, a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided at the point at which the branch circuits originate.

This is not a MWBC rule, but is to require handle ties for more than 1 circuit supplying hots for devices on a single yoke. Note that the circuits need not share a neutral.

300.13(B) Device Removal. In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices
would interrupt the continuity.

This is another MWBC rule that requires the neutral continuity be preserved when a single device is removed. We normally use wire nuts for splices, but for shared neutrals we use buchanon barrel crimps for splices.

/s/ Jim WIlliams

perryx5

Bob, it does not surprise me in the least that the IBEW would support this rule. Good lockout/tagout procedures would make more sense, but then, when has the IBEW ever supported common sense over more regulation. I am neither pro or anti IBEW, I believe there are good and bad electricians both within the IBEW and outside of the IBEW. I received good training from their apprenticeship school, but common sense can't be taught.

azca

I agree that the Code Making Panels seem to be changing the code for those who are untrained or under educated. The is a serious problem with the lack of training required for electricians, inspectors, engineers and architects across the country. To make matters worse many of the people providing training can be rated as poor at best. Add to this the misconceptions, egos, politics and local amendments to the codes and we have a serious problem.

To understand what the NEC, or any code for that matter, requires you must first understand what the CMP, as well as the people submitting the code change, were looking for or better said, what was the intent. The intent for this section was to provide a greater degree of safety for all individuals servicing equipment by reducing the likely hood of shock by de-energizing all phases that share the grounded conductor. Note I said reduce the chance of a shock, not eliminate it. The only way to be sure you will not receive a shock is to de-energize all equipment on the building/property. Anyone who trusts a breaker or disconnect is too trusting.