The Digital MultiMeter (sometimes called an Ohm Meter) is one of the most important tools for installing electric floor heat. Testing the wiring in mats and cables with a MultiMeter can prevent costly repairs by alerting you to any breaks or malfunctions in the wiring of a heating system before you install flooring over it. Check the resistance (ohms) of all mats, cables, and thermostat sensor wires before and after attaching them to the subfloor and again after installing flooring over them.
Follow these steps to check the resistance on your heating mats or cables:
1. First, make sure that all wires are disconnected from the power supply.
2. Set the MultiMeter to measure 200 Ohms (Ω) for 120v mats/cables bigger than 10ft² and 240v mats/cables over 20ft². For mats and cables smaller than this, set the meter to 2,000 (2k) Ohms (Ω).
3. Connect one of the meter’s probes to either the white or black wire of the lead, and then connect the other probe to the other wire. Since you are measuring for resistance (ohms), it does not matter which probe is connected to which wire.
If the meter is working correctly and the probes are properly attached to the wires, a reading will appear on the screen. Check the reading against the Resistance Value found on the product’s tag to make sure it is within the resistance range. (For Nuheat products the range is anything within 10% of the number on the tag.) There is no set resistance value for a thermostat sensor wire. Any reading is good.
Note that readings will vary based on the temperature of the room the mat/cable is in. This is fine as long as all readings are within the range listed on the tag.
4. Next connect one probe to one of the colored wire and one probe to the ground wire (the wire with no color coating). Then test the other colored wire against the ground wire. There should be no resistance reading when testing the colored wires against the ground wire.
If the resistance reading of the black and white wire is off or the meter reads resistance in the ground wire, then there is likely a break in that wiring of the product. The repair kits sold on our website can be used to easily fix most breaks.
If a mat or cable gives you an incorrect reading out of the box, call the manufacturer for technical assistance and to receive a warranty claim number you can use to get a replacement. This is EXTREMELY rare, but not impossible. You can reach SunTouch at 888-432-8932 and Nuheat at 800-778-9276.