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Thermostat wiring - extra wire

Asked Nov 11, 2006, 08:57 AM — 1 Answer
I'm replacing a Honeywell TH110D non-programmable thermostat with a Honeywell RTH230B Programmable. The old one has 6 wires
-Rc (jumpered to R)
-R (red)
-Y (yellow)
-C (green)
-W (white)
-G (blue)
and the new one has Rh, Rc, W, why, and G. I have all those connected as per the directions but there's that extra wire that went into the old thermostat's C terminal. The manual says its "Common wire from secondary side of cooling system transformer" and "Optional when thermostat is used with batteries." , and the wiring diagrams label it as "Optional 24 VAC Common Connection". Since our old thermostat was not used with batteries this was powering the display (new one is batteries only) is it ok to just tape this wire off, or do I need to disconnect or ground or jumper it in the furnice too?
Thanks!

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NorthernHeat Posts: 1,457, Reputation: 699
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Nov 11, 2006, 11:36 AM
Yes the new stat doesn't use a common wire since it doesn't use 24 V. To power it just tape it off.
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