Class 2 product?

[Shpark]

If you have say a metal based lamp and it’s still a class 2 product. What would happen if the exterior somehow became live. There’s obviously no path to earth?

 

[ChipFanDave]

I don’t think that’s how double insulation works. It’s not literally a cable with 2 layers of insulation. It’s what surrounds the terminations inside the appliance.

That is exactly how it works. You have a active/live part surrounded by the basic insulation and then by supplementary insulation.
Look at the cable supplied with class 2 equipment it usually simple flex, inner and outer insulation.

 

[Shpark]

That is exactly how it works. You have a active/live part surrounded by the basic insulation and then by supplementary insulation.
Look at the cable supplied with class 2 equipment it usually simple flex, inner and outer insulation.

Yeah so a class 2 appliance has a 2 core cable which has an outer sheath and then the insulation for both live and neutral, separate ofc! So 1 layer of insulation. It is then terminated inside an insulate box/container/whatever. So one insulation is the cable and 2 is the termination box

 

[ChipFanDave]

No the cable has two layers of insulation.

 

[Shpark]

No the cable has two layers of insulation.

The sheath is not insulation. Insulation is the brown and blue layers over the copper. GCSE PHYSICS - Mains Electricity - What is Double Insulation? - What is the Symbol for Double Insulation? - Which Appliances are Double Insulated? - GCSE SCIENCE. - https://www.gcsescience.com/pe38.htm

 

[Darkwood]

Double insulated cable is slightly misleading term although not exactly incorrect. The insulation surrounds the conductor directly, the sheath is the environmental protection and yes it has insulating qualities that may match the actual insulation itself but is also will be design to cope with the expected environmental conditions to which it is normally installed.

I use specialised cables a lot in machinery and the sheath of which there may be several layers are all designed to ensure the insulation is protected and maintained and is not subject to anything that may break it down.

You are not technically incorrect to use the term double insulated as that is one of its attributes but if you were to do my job then that term would not suffice and they would be clueless to which cable I wanted.

 

[Shpark]

Double insulated cable is slightly misleading term although not exactly incorrect. The insulation surrounds the conductor directly, the sheath is the environmental protection and yes it has insulating qualities that may match the actual insulation itself but is also will be design to cope with the expected environmental conditions to which it is normally installed.

I use specialised cables a lot in machinery and the sheath of which there may be several layers are all designed to ensure the insulation is protected and maintained and is not subject to anything that may break it down.

You are not technically incorrect to use the term double insulated as that is one of its attributes but if you were to do my job then that term would not suffice and they would be clueless to which cable I wanted.

The way I understand it and a square within a square symbol details is what I have said above. I get what you’re saying though. I was just stating that the outside sheathed is not insulation.

 

[DPG]

The way I understand it and a square within a square symbol details is what I have said above. I get what you’re saying though. I was just stating that the outside sheathed is not insulation.

Don't forget double insulation requirements can also be satisfied by one layer of 'reinforced ' material.

 

[Julie.]

Class I and class II (we shouldn't really use 1 or 2) can only refer to the product / appliance not the cable. As stated above cable does not actually comply as class II, even though it may indeed have two independent layers of insulation.

The current approach is to protect for a single fault, that's the whole principle of the wiring regulations, and pretty much all other associated standards - IEC 61140 included.

Thus class I if the insulation fails, it uses ads - there is no further faults considered, as a product you don't supply additional earthing arrangements etc to cover the case that the cpc isn't connected.

Similarly class II if the insulation fails, it is a second layer of insulation (or reinforced) - no further faults are considered.

If the cable enters a class II product without sufficient protection to ensure compliance with class II, then it is a poorly made product, or not compliant at all i.e. a cheap knock-off - it doesn't mean that the principles of product classes is incorrect