I’ve researched/revisited countless MWBC topics today and in the past and believe I know the answer to my question, I’m just looking for confirmation on my observations today at an inspection and making sure that there is not an exception for a component that is used somewhat intermittently. I’ve been working really hard to become proficient in understanding MWBC’s and reporting on them correctly.
1995 build, SFH. I observed what appeared to be a MWBC on a single-pole tandem breaker. I was able to trace the black & red to the same sheathing/cable, ie. shared neutral. The red and black hots are labeled dishwasher and disposal respectively. The two poles did not have a handle tie. Looking at the single-pole breakers to the left, I’ve determined that this breaker/these two hots are on the same leg ((phase; trying to stay away from that word)).
My thoughts…
-Handle ties weren’t required until the 2008 NEC update so I would mention the handle ties in my report as a safety issue but stating that handle ties weren’t required when the home was built.
-The real safety issue is the two loads sharing a neutral on the same leg, correct? The current is combined from both the dishwasher and disposal and may overload the neutral? Is there an exception when the disposal is an intermittent device/not used for very long durations?
Are my observations and understanding correct? Write hard on the same leg/overloaded neutral issue?
There is no exception and yes the issue is that the neutral current would be the sum of the two branch circuits ungrounded conductors. The fact that you traced the two conductors on the twin breaker back to the same cable confirms that you do not have a MWBC. It would be a simple fix to just swap one conductor with the circuit breaker above it.
Unfortunately, not with 100% certainty, more like 96.5%. I traced those wires very carefully but they were packed tight. With my headlamp and cheaters, they appeared to be the same cable but your thought is a possiblity.
Woe, what!?
Thanks for asking Ryan, I’m about to get really confused
How would you verify? Flip both breakers and test at the split outlet under the sink. If one is still hot it is OK.
An alternative if you have a “wiggy” or DMM measure the voltage across the shared breaker terminals. 240v is what you need to see. No voltage indicates an improper MWBC.
Out of curiosity what wires are on the upper left hand breakers? Kinda looks like MWBCs with missing handle ties and/or sharing a single breaker spot. Good catch, sub panels seem to have issues with more frequency than service panels
Good observation. I noticed those as well but I wasn’t able to trace those wires to a single cable, ie. undetermined. Those are at least on separate legs/phases, even if a MWBC. A handle tie wouldn’t have been required when the home was built but would still make it in my report if I was able determine it was in fact a MWBC, which I didn’t.
The NEC required a common means of disconnect if both hots landed on a single yoke for many years.
Robert M is correct, although you may get one person that will say there is no MWBC since there is not voltage between the hots which ignores the fact that it is possible to miswire one and create the hazard of the potential overload of the neutral.
What you have is not a MWBC. It is two circuits on the same leg sharing a common neutral. There is one section of the NEC that allows a single neutral for multiple circuits but this isn’t it. If the two ungrounded conductors are on opposite legs it then becomes a MWBC.
Thank you for the clarification Robert! I understand and can live with that.
So for us Home Inspectors that are creating narratives for these situations, is there specific nomenclature or a term that us HI’s should use for “Two circuits on the same leg sharing a common neutral” or just write/narrate exactly as you stated? That’s what I think I’m being informed of. I’m totally fine with either case
Edit: This is so much fun! My understanding now is that its only considered a MWBC if its wired correctly as a MWBC. Otherwise, it was a poor attempt at wiring a MWBC or just improperly wired and an overload/fire hazard?
