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    kw8n's Avatar
    kw8n Posts: 1, Reputation: 1
    New Member
    		  
    #1

    Dec 12, 2009, 04:46 PM
    Mears m21
    I have M21 SP thermostats through the house here (built in 1978). Single pole switch.
    Of course the two heavy leads (Blk and Red) are for the source and the load for one side of the 220 V circuit.
    There is also a lighter gauge white wire. Where should that be connected in this configuration? Right now it is on the other side (the unswitched side) of the 220 V line.
    Or is this some sort of "ground" and really should be connected to something neutral (such as the earth ground or at least the neutral)?
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Dec 12, 2009, 05:23 PM
    https://www.askmehelpdesk.com/heatin...ls-313584.html


    You might also have to search Google for a wiring diagram for that thermostat or post a picture of the one you have.
    headpin8's Avatar
    headpin8 Posts: 1, Reputation: 1
    New Member
    		  
    #3

    Feb 5, 2015, 09:49 PM
    I also need help wiring a Mears M21 SP thermostat.

    THX
    Ken
    ma0641's Avatar
    ma0641 Posts: 15,675, Reputation: 1012
    Uber Member
    		  
    #4

    Feb 6, 2015, 07:30 PM
    See the post above your's
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