[mudworm]

We moved in to this old house five years ago. There are still a lot about the house that we are trying to figure out. We are going into a kitchen remodel and need many new branch circuits (after a service panel upgrade).

One thing I find out (and am surprised by) is there is a ~30' rigid conduit (or is that an EMT? I'm not sure.) running form the panel to a wall close to the kitchen in the crawl space . Inside the conduit (about 1" OD), three wires (black, red, and white) run all the way from panel to the junction box at its end. But at both ends, each wire is capped with a wire nut. The wires have label: 10, TYPE TW, so I assume they are all 10 AWG wires.

My question is, can I use these existing and unused wires for two multiwire branch circuits? My plan is I will connect a 14-3 NM cable with these wires at the junction box, and run the cable to a duplex receptacle in the sink base. That way, I will have one 15-AMP circuit for the dishwasher, and another for the instant hot water dispenser. At the panel, I will install a 2-pole 15 amp circuit breaker. Will this setup comply to NEC code?

If yes, the follow up question is what about grounding? I know that the white (neutral wire) is grounded at the panel, but what I'm confused about is, if I just pull a separate 15 Amp circuit using a 14-2 NM cable, the cable includes a copper (ground) wire that I will use to connect to the ground terminal at the receptacle. But with the above setup, I will not have separate ground wire, right? In that case, how do I ground at the receptacle that's to code?

Thank you in advance!

 

[Techy]

hook the romex ground to the metal box, the metal conduit is serving as the ground for the existing items

MWBC's are completely legal

 

[mudworm]

Thanks Techy. I'm pulling a 14/3 NM from the metal junction box (with the three 10AWG wires ended). So, I assume I just connect the copper wire to the metal boxes on both ends and I'll be set (code wise), right? Oh, does it matter (to the inspector) as far as grounding is concerned if the conduit is RMC or EMT? I admit that I can't tell by looking at it.

I know now that MWBC is legal, and apparently, it offers many benefits. But why is it not used everywhere? (e.g. there is no MWBC in our house right now). Is it just because of the potential damage it could cause should the connections not be made correctly? I am just wondering if there are other disadvantages I'm not aware of. Since we need to pull many new branch circuits, I'm seriously considering this approach.

 

[AllanJ]

YOu would get a little more use out of those wires if you add on 12 gauge wires and use it as a 20 amp circuit.

Or add on 10 gauge wires up to a subpanel in the house where you have four 15 or 20 amp breakers and give it a 30 amp double breaker (double wide with 2 handles tied together) in the panel.

 

[mudworm]

Thanks Allan. Unfortunately, this setup is in our crawl space. I simply cannot find any space with enough clearance to put a subpanel.

Good point about making the most out of these wires. I will need a separate 30A circuit for an oven, and a 20A circuit for a built in MW oven (stacked on top of the oven in a double oven cabinet). Is it okay if I extend two MWBCs for the two ovens from these three 10 AWG wires? And for MWBCs (a 30A circuit and a 20A circuit), how should do I do the circuit breaker(s) at the panel?

The MW Oven (along with many other appliances I'm buying) requires 15- or 20-amp circuit. Is it a good idea to always use a higher capacity circuit (20 amp in this case)?