What constitutes double insulated?

[Diver300]

I've bought a couple of pendant lights recently, and neither had the metal parts of the lamp earthed, and the cables were only two cores. Both lights have plastic bulb holders, but the wires are threaded through the metal parts to get to the lamp holders.

I wondered what physical features are needed to warrant the claim that something is double insulated. Is it simply an extra bit of heat-shrink?

 

[Lightium]

Double insulated from what?

 

[Diver300]

Double insulated from what?

"Double insulated" is a common term for a Class II electrical appliance. https://en.wikipedia.org/wiki/Appliance_classes#Class_II

 

[Pommie]

Doesn't that answer your question?

Mike.

 

[Diver300]

Doesn't that answer your question?

Mike.

I was looking for something about details of construction.

In a metal pendant light which has an earth tag on the metal ceiling part, I would have expected a 3-core cable earthing the metal of the hanging part. There was a 2-core cable, with joints inside a thin metal tubing, where the wires had been pulled through and round corners, with plenty of opportunity for the insulation to have been damaged. If there was any damage, it wouldn't be possible to see.

 

[crutschow]

the wires are threaded through the metal parts to get to the lamp holders.

I believe that would disqualify it from being classified as double-insulated.

For that, there would have to be another layer of separate insulation between the wire and the metal.

 

[Diver300]

I believe that would disqualify it from being classified as double-insulated.

For that, there would have to be another layer of separate insulation between the wire and the metal.

The wires in the flex didn't go all the way to the lampholders. There was a soldered in-line connection, with tubing and heat shrink around it, inside the metal tubing, to some wires with stiffer insulation, which connected to the lampholders.

I don't know if that stiffer insulation would be counted as "reinforced" so that nothing else was required.

I've fitted a 3 core cable and earthed it all anyhow.

 

[Ian Rogers]

Pendant lights do not need an earth anyhow.. I also agree with Carl.. Heat shrink isn't thick enough to be classed as an insulator.. I would have used normal two core through the tube as "normal" two core is double insulated. Its only in case the tube rubs into the outer core..

 

[Nigel Goodwin]

The wires in the flex didn't go all the way to the lampholders. There was a soldered in-line connection, with tubing and heat shrink around it, inside the metal tubing, to some wires with stiffer insulation, which connected to the lampholders.

I don't know if that stiffer insulation would be counted as "reinforced" so that nothing else was required.

I've fitted a 3 core cable and earthed it all anyhow.

You've now ensured that the unit no longer meets legal safety standards You have also assumed full responsibility for anything which might occur with the unit.

Double insulated refers mostly to the mains lead in this situation.

 

[ronsimpson]

Heat shrink isn't thick enough to be classed as an insulator..

I do not know if heat shrink counts as an insulator. I think it does.
I build transformers and use "triple insulated" wire for primary to secondary insulation. (very thin insulation. 0.4 mm x 3)
I use three layers of transformer tape for insulation (when I use normal wire). 1mm x 3

 

[Ian Rogers]

I do not know if heat shrink counts as an insulator. I think it does.
I build transformers and use "triple insulated" wire for primary to secondary insulation. (very thin insulation. 0.4 mm x 3)
I use three layers of transformer tape for insulation (when I use normal wire). 1mm x 3

Fair dues.. I have a megger sat here on my table, The only heat shrink I have here hasn't a very good insulation.. However! I'm just covering the soldered joint.. Double insulation would be heatshrink over the original pvc coating, so a bad test..