Thank you all for sharing!
So what does the hi-pot device from the heating wire company cost?
These are quite dangerous devices by the way, that's a lot of power at high voltage ...
I could not find the exact one from the heating wire company, but cheap chinese ones is sold for ~500EUR on EBAY.
I may look more into that later, cause.. what's the fun in that.
Dangerous devices indeed. I do not have any plans of playing with this without necessary safety measures.
Use the neon sign transformer to encourage a partial insulation breakdown to finish the job, so to speak, and the isolation transformer to energize the heating cable at a reduced power level. Old-school NSTs have magnetic shunts in the transformer that turn them into current-limited power sources so are almost ideal for hi-pot testing as-is, while supplying an isolation transformer at less than its rated primary voltage will also limit the maximum current it can deliver, though additional resistance or reactance might be warranted for extra safety.
That's a good idea, my first thought was a current limited microwave transformer, but an old school neon transformer sounds better.
Though my guts are telling me that HV DC is better as it is generating a more stable arc while "burning", thus making it more effective.
What's your thoughts on that?
Also, I'm not sure about how much current is needed to generate a sufficient "weld" for lower voltages to pass through, but I guess that will be one of the things I will test on some scrap heating cables when that time comes.
I completely agree with the additional resistance, I'll have to pick up some high voltage resistors.
The only way we could find the break, and luckily it was a ring loop, was to inject a good quality RF signal into the cable and trace out the circuit - then looked for obvious "dips" , "inconsistencies" - unfortunately there were none - then drilled "breaks" in the cable run - re-checked with the RF, and when that didn't help, injected 24VAC and tested a load at the break. A slow process, but worked out ok.
Sounds like a lot of fooling around, but interesting anyway, will look into it.
First of all: this is an underfloor heating element designed for direct connection to the mains. I do not see the point of an isolation transformer here?
One practical reason:
Since the heating cable often is buried on top of a reinforcing mesh which often is earthed (in scandinavia atleast), the current does not have a long way to go before tripping the RCD under these conditions.
If the buried heating element has a break and has gone open circuit, then a constant current source with a high compliance voltage can arc across the gap and produce a hot spot where the gap is. A thermal camera may then be used to locate the hot spot under the floor and let you know where to drill.
That sounds right, though I think a "permanent weld" (like the method in the guide I posted) is better when possible. That way I can supply lower voltages while locating the exact point without having to be using safety equipment. To me it sounds better, although it's a theoretical approach.