Thermostat Wiring

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I would, but I'm not licensed to do mechanical work. Or plumbing/gas. And I suspect the condo association might not be too keen on the idea.

Glad I live in a house where there is no association to deal with. I have gas heat, and not just after I eat chili. :D
 
When a single-pole T-stat breaks one of the ungrounded conductors to a heating element, you don't really have 120-volts to the heating element. There is a voltage on the heating element that is 120-volts to ground, but there is 0-volts across the heating element.

Yea, I know it's just a technicality.
 
Thermostats-Line Voltage

Thermostats-Line Voltage

The 120v lamp lights up on each black wire because the 120v white wire feeds through the LOW resistance of the heater. If you disconnect the 2 spliced white wires and use the test lamp to ground it will light for only one white wire and one black wire. These are the home runs to the panel. The other white and black wire are the load wires. A 1000 watt, 240 volt heater has a resistance of only 58 ohms. A test lamp doesn't draw much current so there is very little voltage drop across the heater and the lamp doesn't appear dim on the load wire.
 
celtic said:
Have you read:
424.20(A) & (B)?
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Yes, that was the basis of my response.

IF you want to use a thermostat as a disconnecting means, then all ungrounded conductors must be opened when placed in the "off" position.

In regard to Bob's statement, and for clarification, the NEC does not require the thermostat to break both lines during the normal course of operation. Only when switched "off" and used to disconnect power from the heater.
 
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stickboy1375 said:
A 240v load won't operate on 120v, it's the same as a 120v load won't operate without a neutral... Even a 240v Tstat will only break 1 leg in operation, but when you move it to the OFF position, then it will break both legs for servicing....
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This is correct. Besides, even a T-stat that did operate both legs, would likely never break both legs at the same instant.

That's one reason 2-pole breakers have a common trip. Even two identical fuses in series will rarely both blow under overload or short conditions.


A 240v heater will operate at 1/4 power on 120v. There are 120v baseboards, but you have to go out of your way to find them.
 
LarryFine said:
This is correct. Besides, even a T-stat that did operate both legs, would likely never break both legs at the same instant.

That's one reason 2-pole breakers have a common trip. Even two identical fuses in series will rarely both blow under overload or short conditions.


A 240v heater will operate at 1/4 power on 120v. There are 120v baseboards, but you have to go out of your way to find them.
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How come it would be 1/4 power and not 1/2?
 
stickboy1375 said:
How come it would be 1/4 power and not 1/2?
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Because when you halve the voltage across a given resistance, the current also halves. Since power is voltage times current, half of a half is one quarter (0.5 * 0.5 = 0.25).

This is also one reason it's such a good idea to run a convertible hottub on 240: you get 6Kw (if that's the rating) of heat instead of 1.5Kw. You get faster heating and you can heat while the jets (hi-speed) are running.
 
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