Need help with SPST thermostat and wiring

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Old 01-05-17, 11:50 AM
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Need help with SPST thermostat and wiring

I bought this, TH115-A-240S-B, which is advertised as a single pole, single throw digital programmable thermostat. However, it has 4 wires, 2 black and 2 red. I am very confused on how to wire this properly because I only have 2 wires in my wall coming to the thermostat box. The current thermostat installed is a double pole analog thermostat and whoever originally wired them in just has the 2 red wires on the thermostat wired together and capped off. Any help will really be appreciated. This thermostat is controlling 2 baseboard 240v electric heaters. 7ft total length of heater on this thermostat.
 
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Old 01-05-17, 12:26 PM
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It sounds like the description is incorrect. Four wires makes it sound like a DP t-stat. Are the wires labeled L1, L2, T12 and T2?
 
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Old 01-05-17, 12:35 PM
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That digital stat is a four wire type. Two wires in for power and two out to the heater.
It may not work on a two wire system.

aubetech/manual/2/TH115-AFSD.pdf

I'm checking now but may not know until later as I'm on the road now.
 
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Old 01-05-17, 02:24 PM
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Thank you very much for the replies and any further info you may have. The two inner wires, one red one black, are labeled L1 and L2. The outer ones are only labeled as load.
 
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Old 01-05-17, 02:34 PM
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The thermostat needs 240 volt to operate. Internally it switches one pole.
Connect L1 & L2 to the hot 240 volt wires. Connect the two load to the heater wires
 
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Old 01-05-17, 05:13 PM
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Electromen...... I'm guessing you missed the part where there are only TWO wires in the box ??

You need a different thermostat..... like a Honeywell TH105
honeywell/Product.aspx?cat=HonECC+Catalog&pid=TH105PLUS/U

or a Honeywell TH106. Both stats run on a two wire switch loop.
honeywell/Product.aspx?cat=HonECC+Catalog&pid=TH106/U
 
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Old 01-05-17, 06:43 PM
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Awesome, thank you for the solid info, Pjmax. The way the double pole analog thermos are in the wall now, with the 2 red wires capped together, what are the consequences of this? Would it mean that even though the thermo dial is twisted all the way to the left and clicked in the off position if the room got cold enough the baseboard heaters would turn on anyway? Again, thank you all for the replies and trying to help me out.
 
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Old 01-05-17, 07:11 PM
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No... the red wires are usually the positive shutoff while the black is the cycling and power off switch. If the stat is turned off..... it's off.

However... since the baseboards are 240v. They cannot be serviced until the breaker is shut off as the stat only opens one hot leg. The other is still connected.
 
 

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