Connecting the common wire to the zone control panel


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Old 06-09-18, 09:15 PM
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Connecting the common wire to the zone control panel

I found out that even though the house is wired with common wire for the thermostats, the wires are not connected on to the zone control panel.

Is there any reason why I shouldn't just connect them? I keep thinking why the contractor omitted this, and if there would be any harm in doing this.

(EWC NCM-300 zone control panel)
 
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Old 06-09-18, 09:19 PM
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There would have been no reason to connect them if they weren't used. The wire is considered a spare. Having an unused common wire floating around behind a stat is a recipe for disaster.
 
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Old 06-09-18, 09:27 PM
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Originally Posted by PJmax View Post
There would have been no reason to connect them if they weren't used. The wire is considered a spare. Having an unused common wire floating around behind a stat is a recipe for disaster.
I see. The common wire is hooked up to all the thermostats though. Not sure I understand how leaving it disconnected at the other end would cause problems. Unless they were anticipating that some homeowner might install a old thermostat might leave the blue wire dangling.

In any case, seems like you are saying that it may be just fine to hook it up if I need it.
 
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Old 06-09-18, 09:50 PM
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You hooked up the wire to the thermostats. The original stats did not use the C..... correct ?
Sure you can connect them if needed.
 
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Old 06-10-18, 06:25 AM
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Originally Posted by PJmax View Post
You hooked up the wire to the thermostats. The original stats did not use the C..... correct ?
Sure you can connect them if needed.
No, not me. The contractor who put in the system, did this. Connected the common wire to all thermostats, but left it disconnected from the zone controller. Which is why I asked if there might have been a reason for him to do that.

In any case, I hooked up the wires, and Nest is working fine now!
 
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Old 06-10-18, 01:35 PM
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I'm lost..... if the stats required a C connection..... they would have been connected.
Some stats have battery backup if the C isn't connected. Pretty silly not to use the C wire if in place.
 
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Old 06-10-18, 07:24 PM
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Maybe power is only from the 24vac transformer in the furnace/air handler. Normally 40va and the installer thought too many thermostats and the zone controller would overload it?
 
 

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