Help with adding common wire (with wiring diagram)

Discussion in 'HVAC Heating & Cooling' started by Underwhere, Jan 10, 2016.

  1. Underwhere

    Underwhere New Member

    Aug 15, 2007
    Milford, New Hampshire
    I have 3 zone valves I'm dealing with.
    Currently with 18-2 wire.

    I ran new 18-5 wire but want to confirm what I need to do to add the common wire.

    I'm going to replace the connections that already exist with the 18-2...and I believe I should connect the new common wires on the 18-5 to L2 in this diagram. So L2 will have multiple wires on it (3 new and 1 original)

    Does that seem correct? I've uploaded a file which accurately depicts my current wiring situation.

    Attached Files:

  2. Stuff

    Stuff Well-Known Member

    Mar 7, 2013
    NO!!! L2 is on the 120 volt side. You only want low voltage (24 volt) going to your thermostats.

    The easiest should be to connect the common to the C terminal on the valves.
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    FWIW, not all boilers or furnaces run on 120vac, so L1 and L2 might both be hot. Regardless, you want to keep your 24vac stuff isolated on the secondary side of the transformer for it to work properly.
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