How do I use the Digital MultiMeter to check a mat or cable?

Make Wiring Worry-Free with a Digital Multimeter!

Whether you’re a DIYer or a seasoned pro, installing electric radiant floor heat may seem a little intimidating. It doesn’t have to be! A digital multimeter (or ohm meter) is an essential tool that you can use to take the guesswork out of installing your new floor heating system.

As a troubleshooting device, a multimeter can alert you to any breaks or malfunctions in mats, cables, and sensor wires in your new system before you install flooring over it, so you can repair or replace wire to avoid re-installation costs and hassles. We recommend using a digital multimeter to test your new system before, during, and immediately after installation for peace of mind. At Warm Your Floor, we believe testing with a digital multimeter is such an important step, we include a FREE digital multimeter with every purchase of a SunTouch kit.*

Read on for tips on how to use this essential tool for worry-free installation:

***IMPORTANT: Before using the multimeter, make sure that all wires are disconnected from the power supply.

  1. Set the multimeter to 200 ohms (Ω) for 120v mats/cables bigger than 10ft² and 240v mats/cables over 20ft². For smaller mats and shorter cables (less than 10ft² for 120v products and 20ft² for 240v products), you may need to set the meter to 2,000 ohms (Ω).

  2. Connect one of the meter’s two probes to either the white or black lead wire. Connect the other probe to the second lead wire. Since you are measuring for resistance (ohms), it does not matter which probe attaches 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 your floor heating product’s tag to make sure your reading is within the resistance range. (For Nuheat products, the range is anything within 10% of the number on the tag.) Cable and mat wire readings will vary slightly based on the ambient room temperature, but they must remain within the range listed on the tag.

    There is no set resistance value for a thermostat sensor wire. Any reading will indicate that the sensor wire is working properly.

    Remove the probes from the lead wires.

  3. Next, connect the meter’s probe to one of the colored wires, and the other probe to the black and white ground wire. (Note: Some mats have a green ground wire. Consult the instructions included with your product for more information.) Then remove the probe from the colored wire and test the second colored wire against the ground wire. There should be no resistance reading (it should show “OL”[overload] or a capital “I” [infinite, meaning “open”] ) when testing the colored wires against the ground wire. If the resistance reading of the ground wire is off, or if the meter reads resistance in the ground wire, then there is likely a break in that wiring of the product.

In the unlikely event that your readings indicate a problem with the product, we can help. Mats or wires that have a bad reading out of the box (before installation) can be exchanged at no cost to you.

If you accidentally damage a mat or heating cable during installation, don’t despair! Call us and we’ll help you choose a compatible repair kit that you can use to easily fix most breaks.

*Limit one per customer.

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