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Checking for breaks
The ohm resistance of each cable should be measured. Make sure the probes of the ohmmeter do not touch
the earth wire at either of the line wire. Make sure you do not touch either of the probe ends, or the meter
will be reading your internal body resistance.
Make sure your ohmmeter is set on the proper scale (0-to-2000Ω for heating cable, or 0-to-20,000 Ω for the sensor
wire).
Your ohm resistance readings should come 10% / -5% of the nominal resistance indicated by the factory
on the UL label.
If your ohm reading is 10% / -5% of what it should be, there is no break. However you still need to check
for an electrical short.
If your ohm reading is lower (outside the range), but there is clearly some continuity, check your ohmmeter
and your batteries. If these are good, there is a possibility that you have several electrical shorts.
If you have absolutely no reading (infinity on your meter), and you are sure you adjusted the setting of the
ohmmeter to the correct reading range (0-to-2000Ω for the heating cable, or 0-to-20,000 Ω for the sensor wire),
then you have a break (total cut) in the conductor.
Checking for electrical short:
In some rare occasions an installation may have suffered from a high pressure point that broke the insulation
between the core conductor and the metal sheath. Such opening in the insulation layer can create an electrical
short, even though the Ohm reading from the line conductor to the other line conductor is normal and does
not indicate any circuit break. In these rare occasions a continuity test will show continuity between the line
conductor and the earth wire, and/or between the other line core conductor and the earth.
There should be no continuity (“infinite” resistance reading, not zero) between the line conductor and earth.
There should be no continuity (“infinite” resistance reading, not zero) between the other line conductor and earth.
If your instrument reveals continuity between both the line conductors and the ground, there is a short in the
circuit.
There are three ways to locate breaks or electrical shorts with underground fault detectors:
1 A break can most easily be found with a “thumper”, an impulse-generating device that generates a sound at
the break point. The thumper includes a stethoscope to locate the exact placement of the break under the
floor.
2 A short can most easily be found with a “time domain reflectometer” tester, which will measure the distance
of the wire between the tester and the short point.
3 Breaks and shorts may generate some heat and they can also be found with infrared cameras scanned over
the floor.
