This is from "heat tape" description on Reptile Basics:
6. If using element in contact with any metal surface, the metal surface must be grounded. A shock hazard can exist as well as the possibility of induced voltage. If using metallic (aluminum) tape to fasten element do not overlap any of the electrical areas in the element- black conductive bars or copper buss bars.
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Be safe, not sorry!
I've used Flexwatt UTH "forever" & only tape the edges (plastic only, non-electrical areas)
Heat tape does NOT have a sticky side.
A heat mat does and is encased in a rubber insulating coating.