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#221709 02/27/22 07:16 PM
Joined: Apr 2008
Posts: 22
Anybody have any experience with Heat Trac stair mats? These have me going crazy! Installed 6 tread heaters and 1 mat last winter. They worked great last winter as far as I know. (No complaints that they were not working, but maybe nobody noticed.) This year, nothing but problems! They supply a power cord with an inline GFI module. Constantly tripping, or the GFCI outlet would trip. I had so much trouble, the owner bought all new tread heaters and a new power cord. Still tripping. I played with them again today and found if I only plugged in three, I could get them to stay on.
So I did some testing since I have six to play with. I found that each mat had a 150,000 ohm resistance between hot and ground, and neutral and ground. Doesn't sound like much, but each mat is leaking .8mA to ground. Multiply that by six and you get 4.8mA of current leakage to ground. I believe GFCI receptacles trip between 3 to 5 mA.. I would also bet the resistance gets lower as the mats get saturated, but have to test that theory!
Interestingly. the installation instructions to not call for a GFCI protected circuit, but, being an outside receptacle, it has to be.
Has anybody experienced similar problems and what did you do to cure the issue?

Joined: Jul 2002
Posts: 8,423
Likes: 3
Are you required to use such a low earth leakage device on something like this.
What I'm saying is, could you get away with something like a 30mA device in the panel and still ensure personal protection?
Also, is the use of an actual GFCI tester mandated where you are, are you sure that the GFCI isn't merely nuisance tripping.
We do use heat trace cables over here on frosty ground outside buildings and from last memory they were a Tycab thing and had something like a 20-50 Watt/per metre dissipation, but to put a megohm-meter on them, they used to give a reading of about 40-80 GigaOhms to Earth @ 500V.
Which if you use Ohms Law, works out to very little leakage current.

Trumpy #221924 09/20/22 08:25 AM
Joined: Apr 2008
Posts: 22
Trumpy, sorry for the late reply. As spring came, obviously my problems disappeared. Now, colder weather is coming way to soon and I need to revisit this problem again.
The power supply is a 120v GFCI receptacle in a weatherproof box with an "in-use" cover. The total load on the circuit is 13.7 amps.
Because the outside outlet is a convenience outlet, it is required to be of the 5MA variety of GFI protection.
My next course of action is to replace my single gang weatherproof box with a two gang weatherproof box, and add a second two gang weatherproof box next to it.
This will give me a total of four GFCI receptacles to plug into. Theoretically, this will allow me to plug no more than two heaters into any GFCI receptacle, thus keeping the leakage current well below the 5 MA trip threshold. I am also going to install a separate in-line GFI power unit on each pad. The pads are designed to only plug into either another pad or a GFI power unit.
Again, this should keep the leakage current well below the tripping level of the power unit.
I also intend on calling the manufacturer to find out what their maximum leakage current is. Should be an interesting conversation.

Joined: Jan 2005
Posts: 5,349
Likes: 1
Cat Servant
Been there, done that.
Ice melt lines — as well as pipeline heat trace tape — leak some current as part of their design. That’s why the instructions specify both a maximum length as well as using THEIR ground fault protectors. IIRC, the “special” protectors trip at about double the level of ordinary GFCI’s.
This gives you two choices: either hard-wire the cables or restrict their length to about half the allowed length.

NEC is deficient on this point. While there exist GFCI breakers set at “equipment protection” limits, code makes no provision for receptacles protected at this higher limit. This means trouble for ice melting lines on the roof as well as for heat tape for n the crawl space.

Code does allow for use of these higher fault limited circuits for machinery, but leaves mandated receptacle limits alone.

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