Wiring two electric heaters to one thermostat

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Old 05-31-07, 10:18 AM
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Wiring two electric heaters to one thermostat

Hi:

This is a room remodeling job--room is 15'x20'. First I'm replacing and repositioning a long baseboard heater--repositioning the heater under a long set of windows at short end of the room. Second we'll have a smaller in-wall unit (with fan) at the other end of the room. Both are 240v. Current 240v line is 20A.

Questions:
1. Assuming that the load for both heaters is 80% or less than 20A, can I run both heaters from one thermostat?

2. Some diagrams I've seen have a thermostat mounted to an electrical work box and that the hot and load lines come into the box. Does this seem like the appropriate design?

Finally, any other suggestions about our choice of heaters will be appreciated.

Thanks.
 
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Old 06-01-07, 12:41 AM
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1. If the total load of the heaters is less than 16 amperes then you may run them both from the same thermostat as long as the thermostat is rated for either 100% of the actual load or 20 amperes minimum. In other words the thermostat would state either on the unit itself or in the instructions that it is "rated" or "listed" for use at 100% of the thermostat rating (at least 16 amperes in this case) OR that it is rated at 20 amperes.

2. How else would you wire it? For 240 volts the electric heat thermostats are usually (not always) two-pole design. Regardless, you have to have the supply be switched by the thermostat to the load.

A 240 heater will have two "hot" leads and a ground lead. Assuming that you have a two-pole thermostat the two hot leads from the circuit breaker will connect to the two "line" terminals on the thermostat. The two leads from the heater(s) will connect to the "load" terminals of the thermostat. All grounding wires will be connected together and if the wiring box is metal the box also will be grounded.

If you have a single-pole thermostat then only one of the hot leads from the circuit breaker and one hot lead from the heater(s) will be connected to the thermostat. The remaining hot leads will be connected together and the grounding leads all connected together.
 
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Old 06-01-07, 05:39 AM
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Thanks for the help!
 
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