OT: Determining Whether Core Drill Severed Induction Heating Cable

[EddyCurr]

What appearance will a late-60's era concrete driveway induction heating cable display when looking at the circumference of a 10-12" dia core cut vertically from the driveway?

If a contractor associated with the project that led to the unannounced coring of the driveway proposed testing if the heating element had been compromised by turning on power to the heating element to determine whether: a) it operated as expected; b) popped the circuit breaker; how would someone respond?

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[EddyCurr]

I have used a simple compass-like nail finder to locate several sites of ferrous material around the perimeter. I realized at the time some of these strikes represented wire mesh and rebar. Later, it was pointed out by the other side that the induction cable would contain copper or (less likely on this property) aluminum as the conductor.

There are no obvious signs of copper or black shielding.

By looking at the controls on the panel, it has been established that these 60 min manually operated timers are 110V 1Ph. Will these timers control the elements directly at 110V or is it possible they control relays and the elements themselves might run at 220V?

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[Peter.]

Ironic that Eddycurr should be asking electrical advice

When you diamond drill copper cables you'll usually be left with a ragged end with the conductor and insulation is dragged somewhat in the clockwise direction. Unless they are very tiny you will see evidence.

Your best evidence will be in the core if it's still around (and they usually are). Wash it off thoroughly with clean water then inspect it.

I once put a 2" core through a 3" sheath full of telephone wires. Took a while to sort out and I was glad not to be responsible for the setting out the hole

[EddyCurr]

Another step has been to sweep the ID of the hole with a Greenlee GT-16 Adjustable Voltage Detector set at maximum sensitivity with no power to the element.

There were alerts, but none that were repeatable in a way that suggested a reliable reading.

I have a higher end stud finder that includes indicator lights for electrical conductors. It is not at hand and I am sceptical that it would offer anything more than the Greenlee.

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[EddyCurr]

Peter. Maybe the handle is not so ironic when one considers the nature of Eddy Currents: 'opposes change', 'transforms more useful kinds of energy into heat' .

The second thing I did after photographing the scene and the miscreants standing around, jaws agape at the new words they just learned was to wheel away the core on my hand truck before it was made to disappear by the parties concerned.

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[J Tiers]

And just exactly what would be wrong with checking the cable with an ohmmeter?

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.

Strongly doubt that any driveway has an "induction heater". Most likely it has a resistance heating element, which is normally fairly small. Look at the CORE not the hole, because the cable will look like aggregate at an angle in the hole. When looking at the core, the ends of the cut cable would be findable, and likely the cable can be identified by finding conductivity between the ends on this "side" vs that "side".

If, as I suspect, it is indeed resistive cale, it will not be either aluminum nor copper, unless you cut the supply cable. Instead, it will be some resistive alloy.

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.

[MaxHeadRoom]

If heating by Induction it would requires something ferrous to heat up, Of course if you parked you car over it on a cold day you could pre-heat it.!
Max.

[Jon Heron]

It will be either a flat or round 2 conductor cable with fine nicrome heater wires in it that will operate at 120V.
If you want to know if its cut, first check for continuity then turn it on and check for a load with an ammeter, piece of cake.
If you had the core the cable would be obvious in it.
Good luck!
Jon

[EddyCurr]

Yes, the element cable is virtually certain to be a resistive type, like a stove/oven/kettle element, not inductive. I am still beside myself since the act occured yesterday afternoon. Thank you for the correction, J Tiers & MaxHeadRoom.

As a follow on to JT's post, I am reading about resistive cable being comprised of nichrome / chromalox alloys. I see today cable comes on spools and also pre-woven into serpentine ready-to-place rolls. One product gives a rating of 12W per lineal foot. There are cautions that severing the cable voids the warranty.

Would the alloy for the element (nichrome or chromalox) be magnetic? Access to the control panel for more than actuation is problematic, due to obstruction. Measuring ohms I presume would be done from behind the panel.

As mentioned, in the dusk of yesterday there was no obvious sign of black or other colour outer shielding visible around the perimeter of the cored pc of concrete or in the ID of the hole. I will be looking again as today improves. From what I've seen of contemporary heating cable, it is not very big in section.

The magnet was locating metals in the core. Is the suggestion that I check for the existance and value of continuity at these points with continuity/low resistance indicating reinforcement mesh/bar and continuity/high resistance indicating element.

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[J Tiers]

Generally not very magnetic if at all. And small enough to make it moot anyway.

I'd be very tempted to turn on and measure for current, but I'd also want to measure resistance. Probably either requires moving the obstructions, whatever they are, so you may as well quit trying to go the long way around the barn.

[EddyCurr]

That's unfortunate.

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

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[Noitoen]

I would switch it on using an RCD as additional protection if the installation does have one. If there is any earth leakage, the RCD will trip, if there is a short, the protection circuit breaker will trip.

[enl]

I would switch it on using an RCD as additional protection if the installation does have one. If there is any earth leakage, the RCD will trip, if there is a short, the protection circuit breaker will trip.

That was also my first thought. It would work if the heat loop isn't isolated from the supply by a transformer (or something else). Fill the hole with water and a little baking soda to make it conductive. Drop an exposed end of a grounded lead into the hole. IF it trips, the line is cut.

Then I thought: why power it? Leave it unpowered. Fill the hole with water and baking soda, drop the lead end into it, run the other end to where the loop ends are, and measure the resistance between the lead and each loop end. If it isn't cut, I;d guess at 10's to 100's of Kohms. If it is, probably well under 1Kohm.

[EddyCurr]

When would RCD's (residual current devices) have begun to be used/required in North American commercial installations? (I say commercial rather than residential because the design philosophy for the home was to over-build.)

If these were introduced after the l-60's, then in the same manner that the house's electrical outlets pre-date ground fault detection devices, the controls for the driveway heaters are unlikely to feature RCD's.

Thank you for the unpowered diagnostic procedures, enl. Access into the panel (and full mobility) would make this a simple undertaking.

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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[enl]

When would RCD's (residual current devices) have begun to be used/required in North American commercial installations? (I say commercial rather than residential because the design philosophy for the home was to over-build.)

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The early 1970's is when they first appeared at all in non-commercial applications, and they weren't cheap. If you have a device of this age, or older, you will likely recognize it. Devices prior to the mid 1970;s were pretty much circuit panel devices if not totally independently mounted. In a system like this, in the 1960's, it would probably have been built into a control box for the system.