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I am a bit in trouble with finding a double insulated 10k NTC sensor and I am questioning what double insulation really means.

Does double insulation mean, that there are really two different isolation materials on top of each other or is it enough, that the insulation material has double the thickness and so double the insulation resistance that is necessary for single insulation?

I contacted several manufacturers and the answere is mostly, that there is no breakdown at a specific voltage, for example 1500V.

Here is also an example from an NTC datasheet I found. Can one say from there if this NTC is double insulated?

enter image description here

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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.

Excerpt of IEC 61010 showing insulation definitions

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.

enter image description here

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  • \$\begingroup\$ Ok, I think I got it. I attached also a datasheet from a NTC manufacturer. The Test from table 5 would be satisfied for safety class II, but since it seems, that only one material is used for the NTC, it is still not safety class II, right? If the same NTC would satisfy Reinforced insulation from table 5, it would be safety class II? \$\endgroup\$ – Hans Nov 21 '19 at 14:12
  • \$\begingroup\$ so, reinforced insulation is better than double insulatuion and would be an acceptable alternative? \$\endgroup\$ – Jasen Nov 21 '19 at 20:02
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Double insulation is not about the thickness of the insulation or its voltage rating — it's about redundancy. There must be at least two independent layers of insulation that must fail before a user is exposed to hazardous voltage.

A nonconducting enclosure can function as one of those layers.

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