wired 120v heater to 240 thermostat

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Mosher

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hi i by mistake wired a 120 volt heater to a 240 circuit when i turned power back on the heater was smoking i threw it out and i will install a 220 heater do i need to be concerned that the thermostat got fried ( in case it makes a difference this thermostat can be used for 120 or 240 )
 

Reach4

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The 240 volt heater powered by 120 volts will put out not much more than 25% of the BTUs it would have if powered by 240 volts.

Mechanical thermostat? If so, I would suspect it is fine. But watch the operation. I would have thought the breaker would have tripped.

Electronic thermostat? Being fried is more likely.
 

WorthFlorida

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With no power to the thermostat (disconnected completely) place an ohmmeter on the two wires that go to the electric heater. You should read an open with the temperature set well below the room temperature, raise the setting above the room temperature and the ohmmeter should read a closure (zero ohms). It's to check that the contacts did not weld together. Digital or mechanical, a 240v thermostat uses a relay that can handle the amperage. The above test won't work if it is a digital thermostat since it needs power unless you can bench test it if it takes batteries.
 

Jadnashua

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In the OP's case, at the same wattage, a 120vac heater will have a lower internal resistance than the equivalent 240vac one, so it will be drawing double the power when accidentally connected to 240vac, which is why it smoked. P=IE. Double the voltage, double the power. That increased current MIGHT have damaged the thermostat. Depends on the specs of the thermostat. It could have fused the contacts closed, or burned them open. If you're lucky, it's neither.
 

Mosher

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should i also test the breaker if yes how would i do that (this circuit has been in service the whole time powering other 240v heaters and they are working fine)
 
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