On 07/01/17 13:52, Graham. wrote:
On Sat, 7 Jan 2017 13:27:27 +0000, Fredxxx wrote:

I've been asked to look at some old Christmas tree lights.

I am confident this will be the of the direct mains type with single
insulated twisted pair and probably conforming to BS 4647:1970.

I am aware new mains lights of this type would have additional
insulation as per BS EN 60335.

Obviously I can only do a visual inspection on them, but what is the
current thinking of single insulated mains cable in terms of PAT or
equivalent testing?

When this has been discussed before, it has been stated that a double
layer of insulation is required, ie a sheath within a sheath. How this
is better than a single sheath of twice the thickness escapes me,
especially if they are both the same grade of PVC.





If the outer sheath is damaged, the crack does not penetrate to the
inner insulation. That's the job of the sheath - mechanical protection
(of a lightweight nature) for the inner insulation.

It is NOT insulation in it's own right, though it usually is made of the
same material and has similar properties to the actual insulation.

Case in point: Old T+E had lead sheathed cables. This of course was not
an insulator