How to Conduct DITRA-HEAT Heating Cable Tests

Electrical testing is one of the most important steps when installing DITRA-HEAT cables. Each test confirms that the heating cable and its insulation are intact, properly connected, and safe to operate. Performing these tests prevents your system from failing, ensures consistent performance, and protects your Schluter system warranty.

Test 1:–Conductor Resistance

In order to perform the resistance test, you must set your multimeter for resistance measurement and take an ohms reading between the two power leads (120V power leads are black & yellow / 240V are black & red).

To do this:

1. Make sure the cable is NOT connected to power or your DITRA-HEAT thermostat.
2. Set the multimeter to the ohms (Ω) range.
3. Touch the black probe to the first power lead and the red probe to the second power lead.
4. Hold steady until the reading stabilizes.
5. Compare the reading to the ohms value printed on the cable spool.

If the ohms reading taken on the two power leads varies significantly (10% or more) from the value printed on the spool, it means either:

• the cable has been damaged
• the measuring instrument is not set properly
• it is simply out of calibration.

The ohms measurement (along with the results of the rest of the tests) must be recorded in your Heating Cable Tests Log on the last few pages of the DITRA-HEAT Installation Handbook.

Test 2:–Conductor and Ground Braid Continuity

The heating cable is protected by a ground braid.  An electrical insulator prevents any contact between the braid and the two conductors. To make sure there is no contact between the braid and the two conductors, you must perform a continuity test.

Using the continuity test (buzzer logo) function of your multimeter, test your cable between the braid and one of the two power leads.

Here’s how it’s done:

1. Ensure the cable is not connected to power/thermostat.
2. Set the multimeter to continuity mode (buzzer symbol).
3. Clip or hold one probe to the ground braid.
4. Touch the other probe to the first power lead (black).
5. If there is no continuity (if the test is successful), the multimeter will display, depending on the instrument used, either “OL ” for “over load” or “I” for “infinity”.
6. Otherwise, if the test fails, neither “OL ”, nor “I” will be displayed and a warning tone will be heard.
7. Move the probe from black to the second power lead (yellow for 120V, red for 240V) and repeat.

Record your test results on the Heating Cable Tests Log on the last few pages of the DITRA-HEAT Installation Handbook.

Test 3:–Insulation Resistance

This test is meant to detect very small breaks throughout the cable insulation.
These breaks often remain undetected during the continuity test since they are not necessarily short circuits between the conductor and the ground braid.
Even small breaks can cause current leakage to ground.

Current leakage is usually detected by the mandatory ground-fault circuitinterrupter “GFCI” (i.e. a thermostat with integrated GFCI or a panel mount GFCI). When a current leakage is detected, the GFCI trips the circuit, thus disabling your DITRA-HEAT floor heating system.

In order to perform the insulation resistance test, you must use a megohmmeter (MΩ), also known as a “megger”, to take an insulation measurement between the braid and one of the two power leads.

Here’s how to perform this test:

1. Disconnect the cable from any thermostat or power.
2. Set the megger to 1000 V test range.
3. Connect the megger’s ground/guard lead to the ground braid.
4. Connect the megger’s test lead to the first power lead (black).
5. Press Test and hold for the duration recommended by your megger (often 1 minute).
6. Read the value: The insulation resistance measurement must be equal to
   or greater than 1 gigaohm (GΩ); 1 GΩ = 1000 MΩ.
7. Repeat for the second power lead (yellow for 120V, red for 240V).
8. If below 1 GΩ, recheck connections. If still low, the insulation may be compromised.

Record your test results on the Heating Cable Tests Log on the last few pages of the DITRA-HEAT Installation Handbook.

Test 4:–Temperature Sensor

Test the floor temperature sensors using a multimeter to verify accuracy of the sensors.

Follow these steps to complete the test:

1. Make sure the sensor is disconnected from the thermostat during testing.
2. Set the multimeter for resistance at 10K Ω +/- 2 (at room temperature).
3. Take a reading between the sensor leads – Touch one probe to each sensor lead.
4. Read the resistance. The resistance will vary according to the temperature (i.e., the colder the sensor, the higher the resistance).
5. Compare the measured values with the table of expected values.
6. If the reading is far off the table value, try again after letting the sensor sit at stable room temp. If still off, replace the sensor.

Record the results in the Heating Cable Tests Log on the last few pages of the DITRA-HEAT Installation Handbook.