So often we find something we have done a certain way for years is suddenly no longer considered proper. This is where we are today with what is called a shared neutral. For many years electricians saved time and money by using a three wire conductor with a ground (12-3 w/g) for house hold circuits. By using the red wire for one circuit and the black wire for a second circuit. We would share the neutral (white wire) and the ground wire (bare or green wire). Thus saving one third of the cost of wire and one half the labor used. Instead of running two standard circuits using 12-2 w/g.
With the implementation of the 2011 National Electrical Code, the rules for a shared neutral for 120 volt circuits changed drastically. A shared neutral is still allowed however, the way we treat them has changed.
Circuits with a shared neutral must now be protected much the same as a 240 volt circuit. The reasoning behind this is simple. For example if the you were to only turn off the breaker protecting the red wire, the black wire would still be energized. Meaning the white or neutral wire could still present a shock hazard.
To avoid this the 2011 NEC requires circuits with a shared neutral be protected by a breaker that shuts both circuits down. If one is tripped or turned off both will be de-energized.. Single breakers may be used if they are UL listed to accept a tie strap. The tie strap makes both breakers disconnect simultaneously. Emphasis here is on UL listed. You cannot use a bent nail or any other hap hazard contraption. The second alternative is to us a factory ganged breaker that is set to trip if either 120 volt circuit is tripped.
Safety Must Always Trump Tradition
Like so many other “safety” advancements, this will be met with moans and groans until it finally becomes the accepted norm. Many electricians will point out that it is not required by local codes. They will probably be correct in saying so. However many municipalities do not implement current codes until they are 6-8 or 10 years old.
Our position is safety is far more important than established norms. After all, my grandfather installed knob and tube wiring in the 1930’s and my father scorned that useless ground wire introduced in the 1960’s. I have to admit I was skeptical of the need for GFCI protection when it was first announced in the 1990’s.
This is a very simple problem to fix and there is no reason not to embrace this chance to improve safety for our customers.