OT: Determining Whether Core Drill Severed Induction Heating Cable

[MaxHeadRoom]

Edit: It appears that RCD (UK/Euro/Aus) is equivalent to GFCI (Can/US). There are no GFCI devices on the property that I am aware of.

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I remember from my electrical days in the UK many decades ago, that practically all service installation also had a metalic fed water supply, so this was used a earth ground as the service company did not provide a earth ground, and if they did, the installer was not allowed to use it, the neutral and the ground wire could NOT be bonded at the service entrance..
Then when these water supplies were replaced or on new installations that used a non metalic water supply, it became mandatory for the use of a RCD at the service panel.
The installer had to measure the earth ground resistance from installation back to the star point grounded neutral.
Not sure how the regulations are there now.
Max.

[Baz]

What is all this fuss about? It is no different from trying a toaster you got in a yard sale. If it is shorted it might blow the fuse and if not you can see it draw current by watching your meter as it is turned on. If it is a single core resistive wire it will likely be open circuit but the area might have several in parallel so will still show some current taken and some areas will still be operational. If it is twin core continuous resistance then it will still take power up to the cut so still be partially working and also likely to be in multiple parallel sections so still showing high power being taken by the rest.
Do rather think trying to electrically heat the earth is a bit extravagant.

[BCRider]

If you have the core I don't see what the problem is. Steel wire mesh or re-bar stands out clearly against the concrete. And any plastic protective insulation around a resistive wire core will also stand out. Wet the core you have with water to make the contrast of colors stand out. If you see nothing that looks at all electrical in nature than you're fine.

If they did cut a line then it would not be that crazy to repair it. Some concrete on each side and a path around whatever is being put into the pavement will be needed to expose the ends and provide a path for a bridging wire. Suitable connections would then be made between a plain copper wire bridging piece and the resistive cables to re-connect the pieces. The slight change in resistance caused by a copper joining link won't amount to diddly in the grand scheme of things. Electricians have various insulating products for doing water tight repairs of this sort.

[Paul Alciatore]

I see no harm in turning it on as a first step. Worst case is if the breaker trips, perhaps with a spark in that hole. Don't have your face in the hole when power is applied. If the breaker trips, the cable is likely bad.

If the breaker does not trip, a resistance measurement WITH POWER COMPLETELY DISCONNECTED would be next. It should read fairly low resistance, probably between 500 Ohms and 5 Ohms. At 5 Ohms it would draw about 23 Amps. At 500, it would draw about 0.23 Amps. If the breaker is larger than 20 Amps, it may read less than 5 Ohms. Open or zero Ohms = bad cable. Over 500 Ohms = bad cable. A reading below 500 Ohms, but not real low would be inconclusive but the higher it was, the more suspect it would be. I would expect such an application to be under 100 Ohms, probably under 50, but those are guesses.

I would DEMAND that they bring the core back and I would break it up to see if there is any cable in it. Alternatively, you could chip around the suspected area in the hole to see what it is. Do that with power disconnected.

[Henro]

I would bust up the core with a sledge hammer and see what I found inside...

Of course you need the core to do this.

[achtanelion]

That's unfortunate.

I am restricted to moving no more than 5-10 lbs for six+ weeks.

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IIRC you're in south edmonton. I'm in greenfield. I assume this is from the Telus rollout? If you'd like help moving stuff away from the panel, I could lend a hand if I'm right and you're close. I'll PM you my number.

J

[J Tiers]

I suspect no big issue, other than gaining access to the wires to measure current. Maybe back at the service box, if the heater is on its own circuit, and the control is not accessible.

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Actually, it may not do anything bad to turn it on, most likely it is open and will draw nothing, or else if multi-section, it will draw less than rated. Unless the cable has both wires, and is "wiped across" causing a short, nothing much should happen, not even heating, unless it is covered in water. Just turn it off again after.....!

You'd need to know what it SHOULD draw, and compare that to the actual draw as measured with a clamp-on meter, to determine if one section is out, for a multi-section heater.
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Oh, yeah,.... if it WAS cut, it is most likely toast, as repair of such cables to be covered in moist concrete is not easy, if it is even possible. There are ways, but no quickie fix job by a contractor is likely to work for long.

[darryl]

Besides the usual resistance checks, you will have the issue of future shorts and electrically induced corrosion if there are leakage currents because of compromised insulation. When dry you could well be measuring the proper resistance and no leakage, and it might heat just as it did before, but when wet- you really do need to know if there's been any intrusion into the sheathing of the system.

[J Tiers]

The main threat is that it was simply cut. If so, and you can isolate the cut section and use the other(s), you should be done, no leakage.

if they cannot be isolated, then you may have an earth leakage issue, one that might force abandoning the entire system. Maybe a qualified installer can chip into the concrete, splice the cable, and properly insulate it. Maybe.

The problematic issue is if it was NOT cut, but the insulation was "grazed" by the core drill. Then there might be an issue of compromised insulation.

If they managed by dumb luck to entirely avoid all the wires, then there should be no further reason to worry, although you can happily let the contractor fry on the hot seat for a while, just for being a dumbshirt. Doleful warnings about "later finding hidden damage", etc etc can be made.

DO NOT sign anything that includes an agreement that all damage has been repaired satisfactorily, until the system is proven to work OK in icy weather. That is totally on the up and up, since you don't know, and he doesn't know, what might have been damaged, even if it appears to be OK.

[macona]

Find someone with a thermal imaging camera and turn it on at night and see if it starts warming up. You should be able to see the path of the heating elements. Thermal cameras are becoming very common now, even home depot carries them. Some attach to the bottom of your phone/tablet.

[pinstripe]

Agree with macona. A thermal camera, especially one designed for building inspections should show you where all the working elements are. Industrial cameras have a wider temperature range, but are normally less sensitive.

The two markers in the image below are only one degree Celsius apart (1.8 Fahrenheit). The dark patch is missing roof insulation.

[CalM]

Jees' em! Flip the breaker and see what happens! through an amp clamp on the feed wires and check for reasonableness.

Making big of something trivial....

[J Tiers]

No kidding.

The thermal camera idea WOULD find a dead section, if there is one, and confirm all the sections are still working, core or no core.

[BCRider]

Eddy, you say you took the core away. Have you examined the cut sides of the core or did you examine the sides of the hole for signs of any wiring being cut? When it comes down to it that is all you needed to do. The core or looking at the sides of the hole would tell you instantly if there's anything other than rocks and sand mixture that was cut.

[Arcane]

Eddy, you say you took the core away. Have you examined the cut sides of the core or did you examine the sides of the hole for signs of any wiring being cut? When it comes down to it that is all you needed to do. The core or looking at the sides of the hole would tell you instantly if there's anything other than rocks and sand mixture that was cut.

What?? And miss the opportunity to generate a thread here? Preposterous I say!