Changing a Chinese flat two pin plug to uk use

[DIYWell]

And it needs to be earthed.

 

[CBW]

And it needs to be earthed.

Why? Is it a class 1 product?

 

[DIYWell]

Why? Is it a class 1 product?

Looks like a metal lamp to me, so wouldn't that need to be earthed?

 

[CBW]

Looks like a metal lamp to me, so wouldn't that need to be earthed?

Probably, but I think it could depend on the batten holder?

 

[bernardgreen]

Looks like a metal lamp to me, so wouldn't that need to be earthed?

If between the metal body and the electrical wiring there are ( at least ) two layers of insulation then the metal work need not be earthed.

One layer ( next to the copper ) provides the electrical insulation and the outer layer provides mechanical "insulation" that protects the layer of electrical insulation from damage.

 

[plugwash]

Layers of insulation is an overly simplistic view.

The design goal is to stop the case becoming live in the event of reasonably foreseeable single faults. Using two layers of insulation is helpful towards that goal. It protects you from defects in one of the insulation layers, it prides additional resistance to wear and tear. But it's not the be-all and end all, other risks need to be considered. What happens if someone yanks on the cord? are there potentially sharp edges that could over time penatrate both layers of insulation?

 

[DIYWell]

Well if it were my lamp, I'd be rewiring it with an earth connection long enough such that it would be the last to disconnect in the event of a hard yank ... just like in a 13A plug.

 

[plugwash]

Agreed, I would not try and build a metal-cased class 2 device without the support of real experts in electrical product design.

 

[JohnW2]

Well if it were my lamp, I'd be rewiring it with an earth connection long enough such that it would be the last to disconnect in the event of a hard yank ... just like in a 13A plug.

I can sympathise with that view, although I've always been a bit doubtful about the theory in relation to 13A plugs (and other things). For the earth connection in a plug to be "the last to disconnect in the event of a hard yank" requires that there be more slack in the earth conductor than in the other two, and I'm far from convinced that such is necessarily the case with the way most people would wire such a plug!

Kind Regards, John

 

[Harry Bloomfield]

For the earth connection in a plug to be "the last to disconnect in the event of a hard yank" requires that there be more slack in the earth conductor than in the other two, and I'm far from convinced that such is necessarily the case with the way most people would wire such a plug!

That requires some deliberate thought and effort from the person fitting the plug. On the few occasions when I now need to fit them, I try to ensure that the L is the core with least play in it's length and the E with the most.

 

[JohnW2]

That requires some deliberate thought and effort from the person fitting the plug. On the few occasions when I now need to fit them, I try to ensure that the L is the core with least play in it's length and the E with the most.

Yes, that's what would be required to achieve the "L breaks first and E breaks last" but, as I said, I doubt many people wire plugs like that.

What I think most people do (often constrained to do so by the plug design), and what the 'instructions' often say (sometimes even with lengths for each conductor specified/illustrated), will result in almost identical amounts of slack in all three conductors.

Kind Regards, John

 

[plugwash]

IIRC BS1363 says when wired according to the instructions earth should disconnect last. Whether the manufacturers actually check this is the case and whether users actually follow the instructions is another matter.

 

[JohnW2]

IIRC BS1363 says when wired according to the instructions earth should disconnect last.

Without looking to check, I think you may well be right - that would certainly make sense, but, as I've said, I'm not sure how one is meant to achieve that ...

Whether the manufacturers actually check this is the case and whether users actually follow the instructions is another matter.

Who knows? However, as I've implied, I don't think that the way in which we wire the plugs, even when 'following instructions' results in any more slack in the earth conductor than any of the others, does it? (and the design of many plugs is such that trying to create such slack might be somewhat of a challenge!).

The only thing I can think of is that the idea is not about 'slack' but, rather, the fact that, because the earth conductor is longer, it will (when the cable is subjected to a 'yank') stretch more than the other, shorter, conductors, and may therefore remain in the terminal for longer - but that would seem to be a fairly iffy argument!

Kind Regards, John

 

[EFLImpudence]

Plugs do vary slightly but if one has the line conductor as short as possible then there is no slack in it and the other two are surely bound to be looser and pulled out later.

 

[plugwash]

Without looking to check, I think you may well be right - that would certainly make sense, but, as I've said, I'm not sure how one is meant to achieve that

By cutting the wires to the specified length. As EFLs pic shows the live conductor has basically a straight shot to the terminal, while the neutral and earth have loops in the which can acommodate a bit of slack. A sideways pull will also likely require more force to pull the wire out of the terminal tha a straigt one.