Double insulation for NTC sensor
I believe this ultimately depends on your problem space and what you're trying to build. The reference I have at the moment is IEC 61010 which defines double insulation as the following.



So the difference is the Double Insulation comprises of some Basic Insulation + Supplementary Insulation.

Reinforced Insulation is an insulation layer(or layers) that exceeds the requirements of Double Insulation.

The breakdown voltage requirements for the different insulation types depend on the voltages present on the line and other clauses from the relevant standards.