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Old 10-14-2012, 04:49 PM   #16
Electric Radiant Heating
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I meant no disrespect. It's just that when working with 240v/20-30a, there's no leeway. I would rather refer than endanger.

That said, the tstat is nothing more than a simple switch controlled by a thermistor. It connects the feed (black) to the load (red) when activated. The white is the other side of the 240v. If the tstat is functioning and it's not tripping the GFI that should be supplied in the Tstat, the line is probably dead, not cut.

This is why I recommended an electrician. If they feel it's 'too hard''s probably a kind way of saying they don't want to have to charge you for not being able to fix it.


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Old 10-14-2012, 04:53 PM   #17
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Originally Posted by beenthere View Post
If you read 120 volt to ground from black to ground, then it can't be shorted/read 0 ohms.
Well - let's just forget that measurement. I must have made an error in measuring the ohms - I suppose there is a possibility of another load on the circuit, but I can't imagine how as it is a 22 amp circuit on a 30 amp breaker - and the heat system in the house is off except for this testing.

I've verified the following:

1. 30 amp circuit, no GFI (home built in '68)
2. Everything I'm seeing indicates this is not like modern radiant floors - it is a single-wire radiant circuit. With one break, the circuit is completely dead. That also means I can't use a thermal imager to locate the bad spot

Seems it is most similar to the single-wire circuits they use for those dog fence transmitters... on them you use a handheld AM radio to detect a generated signal to find the break. I don't want to have to buy a dog fence just to use the transmitter to diagnose my ceilings. Those things are expensive.

3. We're getting power for sure on the black side - although I want to ask, do you recommend I also test white-to-ground by penetrating the wire's insulation?

Last edited by imautoparts; 10-14-2012 at 05:01 PM.
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Old 10-14-2012, 05:36 PM   #18
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Some of the systems wee a single conductor. nickle cupper wire.

You can check the white that way. but it would only prove that one end of the cable is still not broken.
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Old 10-14-2012, 06:04 PM   #19
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Yep - it is a single-wire system. I suppose the new floor radiant wires had to go multi-wire due to the modern GFI requirement.

Here's what I'll use for the patch once I find the broken bits: It has a special coating that allows it to work even if there is no plaster around it as the house settles here and there.

Thanks to a fellow on the electrical forum I've now found the tool I need - a "wire toner". Internet has a DIY type that is targetted to coax tv and phone wire breaks, but it has a transmitter and a handheld sniffer and that's all I need, I think.

Should I even bother to check for voltage at the white wire? I hate to cut it open if it isn't necessary.


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