What kind of wiring to add light switches in condo

Question

I own a Toronto condo, and as a result of a bedroom wall being added after the initial construction, light switches for the living room are inside the bedroom (like that when I bought the unit). I want to add switches at an appropriate place on that separating wall, and thus have to go from the old switch box around a wall corner and a door frame. The construction is metal studs.

I have consulted the CEC, but I'm unsure: what types of wiring are allowed in my case?

I'm moving 3 switches, so at minimum I'll need 7 conductors (not counting bonding). CEC rule 12-106 says: "Where multi-conductor cable is used, all conductors of a circuit shall be contained in the same multi-conductor cable". Does that mean I can't run 3 parallel cables for example? I doubt I can find a 7-conductor cable, so my other option would be single wires in a conduit? The current switch box receives 1" non-metallic tubing, but that seems more difficult to install and the path I had in mind would have 5 90-degree bends, while the maximum is 4 when running wires through it.

Finally, are these condo towers still considered residential or are there different rules to consider?

Answer 1

It's quite likely that being in a multi-unit structure like that, you'll need to work to commercial standards in conduit. Ask when you pull the permit to do the work.

The multi-conductor rule also applies to conduit.

The rule has to do with current loops. All the current going down one cable or conduit must come back in that same cable or conduit. If you sum up all the current in all the wires in a cable, counting the return (neutral) current as a negative number, this must always sum to zero. This is so magnetic fields will cancel each other out.

So for instance you go from

• Cable 0A: always-hot and neutral from power supply
• Switch Box A: switches a hot. Neutral passes through.
• Cable AB: always-hot, neutral and switched-hot
• Lamp fixture B: uses switched-hot and neutral for the lamp.
• Cable BC: always-hot and neutral
• Receptacle C: Uses always-hot and neutral.

Suppose you have a 10 amp heater in receptacle C and a 1 amp light in lamp fixture B. Obviously in Cable BC, currents are equal at 10A hot and -10A return. However in Cable AB, always-hot carries 10A, switched-hot carries 1A, and neutral carries -11A. So even though several wires are in play, currents are equal.

If all you had was 14/2 cable, and you needed to make the connection from A to B, you would run two cables. It would be wrong to use the same neutral wire for both hots in that case since they are in different cables. You would use one hot and its partner neutral for the lamp, and the other pair for the receptacle.

Occasionally you have to think these things through is all.