The new requirements in the 2008 National electric code require multi wire circuits to be on a 2 pole breaker, (3 pole for three phase). Although your state may not have adopted the 2008 code yet.

In your case you should have been fine either way. You were past the splice that broke the circuit up.
The issues are when there are both circuits present in the box, or the neutral is spliced before the circuits are split up.

Having a shared neutral with two circuits is a fairly common practice. You get 2 circuits out of one wire instead of 2 seperate homeruns. Because they share the same neutral the hot leads must be terninated on opposite phases in your service The phases alternate every other breaker stab

petey racer, huh?

Multi-wire ckts do indeed require means for simultaneous disconnect of ungrounded conductors. This is for the very good reason which friend gene 2007 mentioned, safety. If Wireman's correct (don't have my '08 Code yet), handle-straps are out now. Good riddance, says I. Never cared for 'em.

Lone, I don't get the "huh?".

I simply stated that he was working in a box with only one circuit and 2-wire cable. He was past the splice so there was not two circuits present, and there would be no chance to disconnect the neutral for both circuits.

The simultaneous disconnect means was NOT a blanket requirement until the new 2008 NEC. Before that the only time it was required was when the two circuits terminated on the same device yoke, or if the circuit supplied line to line loads.

If you have a 2005 NEC I suggest you look at 210.4 & 240.20(B)(1), particularly the latter.

240.20 Ungrounded Conductors

(B) Circuit Breaker as Overcurrent Device Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.20(B)(1), (B)(2), and (B)(3).

(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.

petey, I read "panel," where you wrote "box." Mea culpa (that there is Latin for "my bad".)

And thanks for the Code reference. I was unaware of these exceptions. However, at the risk of sounding churlish, I'll say in my defense that this gap in my knowledge has cost nothing, and that I am gratified with the '08 change.

Now see here, don't get me wrong, I like multiwire circuits and find them tremendously useful - that is, when it's newer, and professional work (preferably mine, thank'ee very much).

Old buildings, multiwire ckts can be a horror. Way back in the day, Code had no special requirements for simultaneous disconnect or continuity (ie, prohibition against daisy-chaining through receptacles.) Added to that, things got kludged, as they will, and such mischief often led to 240 volts being divided by whatever loads were connected, including my fingers. Damned annoyance, to say the least.

So in the situation I described, if only one breaker was turned off (the one I was working on) there would be no way to get a shock from the shared neutral wire? I assume this is safe because current would not be flowing on this wire because there is a complete circuit elsewhere, but not here.

So in the situation I described, if only one breaker was turned off (the one I was working on) there would be no way to get a shock from the shared neutral wire?

Not exactly 'no way'. If the work you were doing on that circuit was troubleshooting a problem actually caused by an open shared neutral, then the full voltage of another live hot wire sharing that open neutral could be present on the neutral wire.

I wasn't happy about the 2008 change originally, since my work is all commercial construction and service. But when I take into account the residential work, and the DYI'ers who own and work on the results, I guess it's a good call by the NEC. But it marks the beginning of the end of commercial and industrial multiwire circuits supplying multiple loads.

Just curious - Why would this be the end of comm/ind mutltiwire circuits? Doesn't the NEC change just mean that you need to have a double pole breaker? Aren't multiwire circuits still legal?

I don't see it as the beginning of the end either.
Only problem is we will need to use two and three pole breakers. This is an issue in offices and other settings where turning off breakers causes chaos.

I just think that the commercial market will eventually force out the practice. Modern computerized offices can't get any work done with the power off, so separate neutrals will become standard in new construction specs. This are already becoming common, due to the number of non-linear loads from electronic ballasts, printers and computers. NEC-mandated "chaos" will only add to that practice.

From the viewpoint of office managers, the 2008 code effectively requires that circuits powering unrelated loads be grouped on common breakers. The need for additional circuits is often only recognised and addressed when an overloaded breaker trips. At present the effect is only felt on that one circuit, but with 3-pole breakers in use the effect will be far greater. And the inconvenience of work done on one circuit be shared by workers on completely different circuits. And when a new circuit IS added, we will no longer be able to pull a single hot through existing conduit to share an existing neutral with a circuit located across the panel without also pulling a separate neutral.

Businesses go to great expense to install or lease office space with generator backup because of the cost of the loss of power. They will certainly pay a premium price for commercial space powered by individual circuits on separate breakers - requiring separate neutrals be used.

Finally, with increased service market pressure to NOT turn off 3-pole breakers in order to work on a single circuit, there will be more instances in the future of people choosing to work circuits hot - regardless of NFPA 70E - and increasing insurance industry pressure to require separate neutrals on all circuits in NFPA 70.

Posted by scubakirk1 (My Page) on Sun, Aug 3, 08 at 4:31

"Having a shared neutral with two circuits is a fairly common practice. You get 2 circuits out of one wire instead of 2 seperate homeruns. Because they share the same neutral the hot leads must be terninated on opposite phases in your service The phases alternate every other breaker stab"

To confirm what Scubakirk1 stated in the above statement...
If I have a double-pole breaker installed in my service panel, each hot lead would be on opposite phases?

Thanks

"If I have a double-pole breaker installed in my service panel, each hot lead would be on opposite phases?"

That is correct.

Modern computerized offices put UPS's on each device. You can tell when we lose power because while work goes on, the AC goes off and the UPSs all start beeping.