I know not of "Suntouch."
My NuHeat literature, as well as the installation video, are both adamant about megging the mat:
1) when you take it out of the box;
2) when you place it on the floor;
3) after covering with thinset;
4) after setting tile; and,
5) before powering up.
The paperwork also has a form for your use, to note the actual megger readings.
There's a certain logic to it; you want to discover damage as soon as you can, to minimize the costs of replacing the mat- as well as for assigning blame for the damage.
Over at the handyman forums, there is no shortage of threads on this topic. It seems that, despite the best efforts of the manufacturers, all manner of these mats are being 're-tasked' from their original intended use. The manufacturers say 'don't trim,' yet folks try to trim them. Damaged mats are fished from dumpsters- and, amazingly enough, they don't work very well. Folks try to power them up with something besides the factory control unit. It seems every trunk-slammer is out there trying to install these 'on the cheap.'
Sorry for the rant- but, good heavens, FTRTI issues cause more headaches than I can count.
(FIRTI = Failure To Read The Instructions)
yep. all of that.
man knows whereof he speaks.
there is also a "supervisory device" that nuheat sells, that you are
flat nuts not to use... i think they are $30 each.... it's a battery powered
continuity tester that will sound an alarm if the resistance of the mat goes
either dead short, or open. after you have installed the mat and meggered
it, you put this critter across it, so when the tile guys screw it up, or the
plumber, or whatever... you get an alarm, that won't shut off.
you use one per mat, and after the job is done, it goes on a shelf somewhere
for the next time you need it.
now, i'm new, but it seems to me that "low voltage" as in less than 120 vac
seems like a sucky way to heat a floor, as you are gonna have to have much
larger guage wire to the mats.
now, for the box in the wall, for the nuheat controller, you will not be happy
trimming it unless you use a 4sd box, with a 1 1/4" two gang ring, set flush
with finish wall.
you'll want that extra volume of the ring, even in 1/2" sheetrock.
randy