Conclusion: i think the WRAP ON roof cable doesnt work in the long terme with the T3. Maybe because the thermocube turn on and off the cable often. And that type of cable are not made for this, cause these cables was working for at least 3 month. And they are made to be straight and not turned around a trunck.
So, its better to use the HEASYHEAT cable with their own thermostat for the roots system and the trunck/foliage.
By chance, its the end of winter, ive got only 1 heatcable at the ground for each Trachy under mummywrap. Only with the sun, the temp. goes up to 50F when its 20F outside, and go down to 10-20F. And my bigger Trachy looks fine, the other one has a fungus problem, will see if it will survive

Ben