Detecting Electric underfloor heating cables.

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I need to knock a few holes through the screed that is covering the under floor heating cables. Anyone have any idea how I successfully locate the cables so I can avoid damaging them?

Cheers.
 
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There's no reliable way of doing it. You could try one of those detector things but they wont tell you much.
What is over the screed - tiles??

The only option is to lift up a tile and very very carefully chip away at the screed. Its a specialist job to repair the element if you break it.
 
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if the heating is working:

wet-mop the floor and leave it damp. Turn on the heating. You can expect to see the set floor drying out fastest above the hot elements and showing the pattern. You may need to take some photos or mark the floor with pencil or chalk especially in the area where you expect to work.

be aware that floor heating has cold tails from the heating elements to the connector or thermostat which will not be hot but do carry electricity.
 
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The needle of a small undamped compass ( i.e. the needle is not in a fluid filled compass ) may visibly vibrate when directly over the mains energised heating wire.

Having been in a similar situation with finding communication cables this solution worked locating the cables quite accurately.

It may be adaptable to locate the under floor heating cable

We used a DC power supply to feed a DC current through the screen of the cables and then a magnetic compass to detect the resultant magnetic field.

If the heating cable is a single wire element then with due consideration of resistance and maximum permissable current connecting a suitable battery in place of the mains may create a magnetic field detectable by a magnetic compass.
 
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bernardgreen said:
The needle of a small undamped compass ( i.e. the needle is not in a fluid filled compass ) may visibly vibrate when directly over the mains energised heating wire.

Having been in a similar situation with finding communication cables this solution worked locating the cables quite accurately.

It may be adaptable to locate the under floor heating cable

We used a DC power supply to feed a DC current through the screen of the cables and then a magnetic compass to detect the resultant magnetic field.

If the heating cable is a single wire element then with due consideration of resistance and maximum permissable current connecting a suitable battery in place of the mains may create a magnetic field detectable by a magnetic compass.


Nice idea. But so I'm clear. I need to run a direct current through the cables for this to work and not the AC from the mains.

I had thought about scattering some iron filings (to detect a small magnetic field around the lines, but I hadn't considered the AC/DC aspect.

Cheers.
 
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JohnD said:
if the heating is working:

wet-mop the floor and leave it damp. Turn on the heating. You can expect to see the set floor drying out fastest above the hot elements and showing the pattern. You may need to take some photos or mark the floor with pencil or chalk especially in the area where you expect to work.

be aware that floor heating has cold tails from the heating elements to the connector or thermostat which will not be hot but do carry electricity.

Another good idea. Though there is about 10mm of screed above the cable, and I wonder if this would spread the heat out uniformly by the time the heat had permeated that far. Will try this.

Big cheers
 
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I have travertine tiles + adhesive over my cables, which must be over 10mm and I can tell where the wires are by touch as it first warms up. Wetting the floor is an excellent idea though.
 
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CAT & Genny?

Never delt with under floor heating - how far apart do they run?
 
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applesauce said:
Nice idea. But so I'm clear. I need to run a direct current through the cables for this to work and not the AC from the mains.

Yes a DC supply in place of the mains supply. I will have to think about what you would need as I haven't done it with a heating element before.

What power is the mat in watts ? and How deep below the surface is the mat and how close are the wires in the element. Then need a day to try something.

It is probably not going to work on the temperature sensor cable as they will be a pair ( so cancelling currents and no magentic field ) and it would not take the current needed.
 
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bernardgreen said:
applesauce said:
Nice idea. But so I'm clear. I need to run a direct current through the cables for this to work and not the AC from the mains.

Yes a DC supply in place of the mains supply. I will have to think about what you would need as I haven't done it with a heating element before.

What power is the mat in watts ? and How deep below the surface is the mat and how close are the wires in the element. Then need a day to try something.

It is probably not going to work on the temperature sensor cable as they will be a pair ( so cancelling currents and no magentic field ) and it would not take the current needed.



The matts are 160W per meter square, and I have a number matts underneath (2 x 10m2 and 1 X 6m2 and 1 X 2m2).

All of it's buried under approx 10mm of screed ( this is a max and it varies).
 

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