Federal Pacific Thermostat and Baseboard Heater

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  #1  
Old 11-21-11, 02:25 PM
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Federal Pacific Thermostat and Baseboard Heater

Just purchased a house built in 1976. It has the original FP single line thermostats, and electric baseboard heaters. I do not have my meter with me at present; however, I do suspect that the system is 240V.

I disconnected both wires attached to one of these thermostats, turned the power back on, and tested each wire in turn with a simple on/off tester. Both wires read hot.

I opened up the incoming line connection box located on one of the baseboard heaters. With the thermostat not calling for heat, both incoming wires read hot.

I expected one hot lead showing at the thermostat and one hot wire at the heater when heat is not being demanded.

Exactly how is this setup wired?

Thanks in advance for any info.
 
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Old 11-21-11, 03:15 PM
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If by "simple on/off tester" you meant a non-contact tester your reading may just be ghost voltage.

What is your problem? You didn't say? Too much heat or too little heat?
 
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Old 11-21-11, 06:04 PM
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I disconnected both wires attached to one of these thermostats, turned the power back on, and tested each wire in turn with a simple on/off tester. Both wires read hot.
Was that a 2 pole breaker you turned back on?

I opened up the incoming line connection box located on one of the baseboard heaters. With the thermostat not calling for heat, both incoming wires read hot.
I suspect you are right, this is a 240 volt heater and circuit. What is happening is this, you have a simple tester that tests for a hot wire and not voltage. One wire is hot direct from the panel. The other wire is testing hot because power is feeding from the first hot wire through the heating element and back out through the second wire. You are essentially getting the same 120 volts on both wires. If you would test for voltage across these two wires you would read 0 volts, but each wire would test 120 volts to ground.

What problem are you having?
 
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Old 11-22-11, 11:55 AM
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Originally Posted by CasualJoe View Post
Was that a 2 pole breaker you turned back on?
Yep, a Bryant 20 amp with the outer two switches connected and the inner two linked to each other. Going in I just assumed 240V; however, the unusual readings made me step back a bit.

Originally Posted by CasualJoe View Post
I suspect you are right, this is a 240 volt heater and circuit. What is happening is this, you have a simple tester that tests for a hot wire and not voltage. One wire is hot direct from the panel. The other wire is testing hot because power is feeding from the first hot wire through the heating element and back out through the second wire. You are essentially getting the same 120 volts on both wires. If you would test for voltage across these two wires you would read 0 volts, but each wire would test 120 volts to ground.
This makes sense. Last night at 2am, I decided that this was a possible scenario. Nice to have someone else offer a similar solution. I'll be going back to Virginia next week. I will bring back my meter and test for voltage as you indicated above.

I'm changing out the old thermostats. They were installed in 1976 and offer no accuracy whatsoever. Setting temperature is pretty much guesswork. I will be installing Lux ELV4 units throughout.

Thanks to all for your courtesy and knowledge!
 
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