I would appreciate any help or guidance. I'm in Canada and renovating what used to be the laundry room in my older house. I had originally planned on adding an outlet from one of the existing receptacles as part of the renovations. At the panel, a double pole 15 amp breaker with 14/3 wire is clearly labeled and dedicated to the room in question. The panel was upgraded within the last 30 years or so by a professional electrician and there is modern wire running from all breakers.
The 14/3 from the panel ends at the first receptacle in the room, where it runs into the outlet box along with 14/2 wire from a light switch. The red hot wire from the 14/3 is connected directly to the receptacle line, and the black is pigtailed together with black from the 14/2 wire and doesn't connect to this receptacle at all. The white neutrals are pigtailed together, and then feed into the appropriate line on the receptacle. This receptacle was used for a washing machine when the wiring was upgraded, and this is the only reason I can think of why maybe a separate hot wire was reserved for use here?
There are 3 other receptacles currently in this room as well, they are all wired as follows: They each have two separate runs of older NMD-3 12/2 wire that come down from the ceiling (currently hidden by drywall) and run parallel down stud bay into each outlet box. The hots and neutrals are pigtailed together, then connect to the lines on the receptacle. There are no wires connected to the load side of any of the plugs.
I'm familiar with running 12/2 and 14/2 to outlets and thought I had a basic understanding of typical wiring but what I've encountered here has me confused and intrigued. My first thought is that this was a type of multiwire branch circuit but it doesn't seem to fit with what I've read on those either. Is the double pole breaker being used to serve the room lights+plugs and also the washer plug as 2 separate 120v circuits? Why would 14/3 and a double breaker be used instead of just 14/2 and single pole breakers? Why the two runs of 12/2 into the other receptacles? Can I safely use 14/2 to add another outlet from the unused load side of the first plug that previously served the washer?
Thanks again for any help or clarification you can provide.
Best Answer
Well it IS a MWBC. It just happens to be one that serves one outlet on the one side, and (presumably you've checked that the other outlets do actually turn off when the breaker does) the remainder of the outlets and the lights from the other half. It still economizes the wire from the panel to the room (one 14/3 rather than 2 14/2's.)
The older 12Ga wire presumably just means that the older outlet wiring that was not changed out was done with 12/2, and might have been on a 20A circuit at that time. Since it's more than large enough for 15A, that's perfectly safe in the current arrangement. Likely the two runs of wire are in, and on to the next device in the chain.
Personally, I find the combining of outlets and lights to be a thing I object to (since I don't like getting left in the dark, and fixed lights almost never trip a circuit breaker, while outlets get whatever plugged into them until they do) but electrical codes in both of our countries don't care about that.