Earth for steampunky Coughtrie metal lamp

[MrsRenovator]

I had an old Coughtrie outside lamp replaced with a floodlight, so i thought i would make an indoor task light with the old fitting, a sort of steampunk style but without me having to wear victorian clothes.

It still has the original ceramic lampholder, which is fine, but no eath lug. I suppose it was so high up, no one could reach it outside. That and the fact it was the 1950's.

Ive drilled a hole in the lamp, near the lampholder, and am going to crimp a ring crimp onto the earth, and will test for continuity between plug and body.

What i want to know is, what is the principle for needing an earth? Is there less resistance through an earth cable than through a human body? And if i was fitting a new metal lampholder, (which im not) why is the earth on the lampholder rather than directly onto the lamp? And what is the main danger that the earth is trying to prevent? Is it from sticking your fingers into the lampholder? Or is it from frayed wires making the lampholder/lamp live?

Any and all answers welcome.

Thanks

 

[MrsRenovator]

 

[EFLImpudence]

what is the principle for needing an earth?

So that if a live wire touches it, it will cause the protective device to disconnect the supply.

Is there less resistance through an earth cable than through a human body?

Yes, a lot less but that is nothing to do with it.

And if i was fitting a new metal lampholder, (which im not) why is the earth on the lampholder rather than directly onto the lamp?

Presumably the lampholder is connected to the lamp body.

And what is the main danger that the earth is trying to prevent?

As above, before you touch it.

Is it from sticking your fingers into the lampholder?

No, it doesn't protect against stupidity.

Or is it from frayed wires making the lampholder/lamp live?

Yes.

 

[MrsRenovator]

stupidity

 

[MrsRenovator]

Thanks for all that. Comprehensive answers.
Just made me think of a couple of other things...

So if there was a grommet or plastic washer at the base of a metal lamp holder, preventing continuity , you'd have to earth the lamp body aswell?

And would paint affect the earth? I realise I've painted quite liberally where my new earth lug will go.

 

[EFLImpudence]

So if there was a grommet or plastic washer at the base of a metal lamp holder, preventing continuity , you'd have to earth the lamp body aswell?

Yes, or remove the washer.

And would paint affect the earth? I realise I've painted quite liberally where my new earth lug will go.

Yes, it would - scratch off some paint so that there is metal to metal.

 

[rsgaz]

scratch of some paint

"scratch have some paint", do you mean?

 

[EFLImpudence]

Thanks.

Typo corrected.

 

[333rocky333]

Was there not a threaded hole for terminating the earth. located beside the lampholder

 

[RF Lighting]

There should be.

This is a slightly different model but all coughtries are pretty similar.

 

[securespark]

Is it possible the 50's Coughtrie fittings did not have an earth terminal?

 

[MrsRenovator]

Mine looks a bit different. But heres a photo showing the hole ive drilled on a sort of lug, Maybe the earth was supposed to just wrap aroung it,

 

[MrsRenovator]

Now ive got 2 more snags.

!. The metal body doesnt seem to conduct a current so im not getting continuity anywhere at all. Maybe a good thng.

2. I cant think how to make a cord grip. Maybe push a cork in the base after wiring it?

 

[MrsRenovator]

Ok. Finished. Found a 15w pygmy lamp in a drawer to test it. Woah, it's too bright without a shade!
I wonder if they make those gold vintage type LEDs in pygmy?

Anyway, I'm very pleased with it. And it only cost the price of the fancy braided cable and a plug. I used leftover bits of paint.

Are Coughtries aluminium then? But I thought even aluminium conducted electricity.

So if you think that the poor conductivity of the metal might make my earth lug insufficient and a danger, I'll spend a couple of quid and buy a double insulated lamp holder. What do you think?

 

[winston1]

Could it be anodised Ali? The anodise coating does not conduct but the metal underneath does.