Ran across this today. 12/3 w ground and 14/3 w ground being used on separate circuits(both hot legs to different breakers). Since they are sharing a neutral, shouldn’t there be handle ties so that both breakers using the same neutral are shut off(or trip) at the same time? There were about 5 pairs of these in the panel and only one pair had a handle tie. Had the same situation last week, but all shared breakers had the handle ties installed.
Thanks in advance!
Multiwire branch circuits. Some love them some hate them.
I have used them all my life and think that they are a very good money saver as they eliminate one conductor.
If the multi wire circuit is hitting two circuits such as the two small appliance circuits for a kitchen or two general purpose circuits such as the living room and bonus room so on and so forth then single pole breakers are fine for the install before the adoption of the 2008 code cycle.
Multiwire branch circuits that supply only one device such as one receptacle used for both the disposal and dishwasher must open both circuits simultaneously (handle ties or two pole) and multiwire branch circuits that supply only one piece of equipment such as ranges and dryers shall have common trip (a two pole breaker)
After the adoption of the 2008 code cycle any multiwire circuit including those in commercial and industrial installations must open all circuits simultaneously.
Also the rules governing Arc-Fault and Ground Fault Interruption will limit the use of multiwire branch circuits in a dwelling unit.
With all this said and being an electrician I would not mention multiwire circuits in a report unless I found a situation where both circuits of the multiwire circuits was being fed from the same leg of a panel. This will be easy to identify as the neutral will be discolored from the extra current it will be forced to carry.
If the 2008 NEC or ICC is adopted in you area then it could be written up as not complying with today’s standards but then the electrician that is called in will only say that there is nothing wrong.
Thanks Mike!
I have found them with no signs of discolouration as they served bedrooms, living room, dens, etc…rooms usually with no high draw appliances/lights that may run the #14 neutral wire at 15+ amps. It would take the simultaneous operation of higher draw appliances/lights over a period time for the discouloration to occur. This is a situation that is still a future potential hazard as the next family may run the house differently to begin the overheating/deterioration process.
Good point you make here. What I was pointing out was one that would be easy to find without having to dig through a lot of spider webbing to find it.
The 2008 has attempted to make this multiwire “spider web” easier to sort out. It now requires that the two hot legs be grouped so you can see that they go to oppisite phases more easily
Great move. Sometimes it can take 5-10 minutes just to trace these pairs to make sure they’re on opposite phases.
I have done this for years with conduit work.
I HATE it when guys don’t bundle MWBCs and there are several in a shared conduit. :mad:
You can spot them easily when they got it wrong. The whites are burned brown at the neutral bar, often times.
I always marked them in bundles too. Just makes good sense to me, and only takes a few seconds.
Eight years ago I changed one duplex in a living room. Well the ground was shared between two phases and i ended up burning out 300 dollars in electronic gear from disconnecting this neutral. A few years later I exactly understood what I had done. Yeah I know…turn the power off first! 