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Posted By: nhsparky Ice melting mats - 02/27/22 11:16 PM
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?
Thanks.
Dave
Posted By: Trumpy Re: Ice melting mats - 05/28/22 07:54 AM
NHsparky,
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.
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