Electrical – run THHN for separate washer and dryer circuits through the same conduit

electricalwiring

I am relocating a 120V washer and 240V dryer from the basement on south side of my house to the basement north side.

  • The current wiring is one 110V 20amp circuit with dedicated circuit breaker and one 240V 40amp circuit with dedicated 40 amp dual breaker.
  • The wiring for both circuits runs out of the panel box into one 3/4" conduit to the receptacles (first receptacle in line is the 110V and terminating with the 240V 3 prong receptacle for the dryer.)
  • I also plan on removing the old circuits.

I have two questions:

  1. Is it still within code to run all the THHN wiring (12 gauge for 110 and 10 gauge for 240) or should I run two separate conduits for each circuit as one will be 20 amp and the other will be 30 amp?
  2. My current dryer has a 3 prong receptacle (2 hots and 1 neutral). The NEC code since 1996 states that all dryer circuits 220V for house dryers need the 4 wire (2 hots, 1 neutral, and 1 ground). My house is 1925. So in converting from an 3 wire to 4 wire plug and receptacle where do I attach the new ground wire on my old dryer? And does the ground connect into the neutral bus or the ground bus?

I will need to get a permit here in Oregon and I am not a licensed electrician.

Best Answer

  1. It is permissible to run more than one circuit in a conduit as long as the conduit is sized to carry all of the current carrying conductors. In your case a 1/2" conduit should do it, but I would go with a 3/4 for ease of pulling.

2(a). One of the advantages of pulling in one conduit is that you would only need a single grounding conductor sized to the largest circuit.The ground is attached to the receptacles and any metal enclosures and there are places marked for that purpose. You will attach the ground to the neutral bus in the main panel. You might check to see if there is a proper ground in the panel and make any necessary upgrades.

2(b). Most jurisdictions require any work to be permitted and installed by qualified personnel. We really can't be certain of every jurisdiction since codes vary by state and municipality. A quick call to your AHJ can solve that problem.

Good Luck.

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