Can I shorten my in floor heating cable?

Home Improvement Asked by JollyGoodTime on December 16, 2020

Just wiring up an in floor heating thermostat. I have two separate two wires going into my flooring as well as another coming from the panel.

I am wondering about the two wires going down to the flooring.

Wire 1: Is the sensor for the floor.
Wire 2: Is the heated wires for the floor.

So can wire 1 be ran close to wire 2? In the instructions it says that the sensor (wire 1) should not be ran with the heated load cable (wire 2). It looks like both cables are coming into the box through the same hole so I am not sure how the previous person on this new instal did the rough in but it looks like they are ran together. Is this going to be a big problem?

Also wire 2 (the heated floor cable) is about 4 feet long in the thermostat box. There is a tag close to the end of it that says to not remove that tag with some ampacities etc on it. So it makes me think that I cannot cut the extra 4 feet off and must coil it in the box (maybe it needs that set resistance of the cable to operate properly?). But thats a big bundle of wire to heat inside the device box so I just wanted to check.


2 Answers

Usually the sensor wire is not rated to be run in close contact with the resistive portion of the heat wire or pad there is usually a section that is not for heating but for the electrical connection. This kind of wire can be run in close proximity to the sensor (through the same hole in the control box and up the wall) both of these wires can be shortened if this is the case. I do agree with archonosx about following the manufactures instructions.

Answered by Ed Beal on December 16, 2020

The sensor is usually a 10K ohm Negative Temperature Coefficient thermistor and changes its resistance with temperature. It is not that sensitive to the electromagnetic interference from the power cabling. (Analog signal cabling is routinely separated from power cabling.) Good idea in this case but not that critical.

The lead wires to the heat cable should be standard copper wiring and should be able to be cut to length. It is the mat under the tile that has the resistance and gets warm. Usually the "do not remove" tag says except by the installer/user/homeowner. But I but the tags off my furniture too.

Best thing would be to find out what manufacturer of heat mat you have and find the installation manual for it. The National Electrical Code states you must follow all manufacturer's installation instructions. Good luck.

Answered by ArchonOSX on December 16, 2020

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