Rewiring antique lamp

[andimac101]

Hi

Quick Q- I am rewiring a 70 year old brass swivel top desklamp. It is quite simple, new flex will run through the body to connect to a new lampholder in the top with an inline switch in the flex. The Old lampholder has no earth but new one does.

Should I use 3core flex and wire in the earth or 2core and wire it as it used to be?

Thanks
Andrew

 

[sparkwright]

You must use 3 core round flex and make sure you earth the metal lampholder. You must also make sure all metal parts will be earthed as you do this.

Will the swivel part cause part of the fitting not to be earthed? If so earth both parts,

 

[andimac101]

Thanks for that- the wire will run straight from the lampholder down through the body of the lamp and out to an inline switch, so there won't be any break. Presumably this will be adequate when earthed on the lampholder then?

 

[IJWS15]

Thanks for that- the wire will run straight from the lampholder down through the body of the lamp and out to an inline switch, so there won't be any break. Presumably this will be adequate when earthed on the lampholder then?

That is not what Sparkwrite said:

You need to make sure that each metal part of the lamp is adequately earthed - the joints in the lamp may not conduct very well in which case you will need an earth stud on each part of the lamp.

Having an earth connection in the lampholder does not mean that the metal frame of the lamp is all earthed.

 

[andimac101]

Ok, so I've got to earth each metal part. Having not done this before what do I need to do?

 

[sparkwright]

You only need to earth each part if they are joined together by something non conductive.

All exposed metal parts need to be earthed.

Can you send photos, or describe the fitting a bit more in detail?

 

[andimac101]

lamp

• andimac101
• 13 Nov 2011
• 1

I will be replacing the lampholder and the wire, additionally wiring in an in line switch. Access can be gained from underneath and the construction is brass.

 

[sparkwright]

If all the metal work is joined together, and the metal lampholder is in direct contact to the metalwork, earthing the metal lampholder alone may be enough.

If in doubt do a continuity test between each piece of metal and the earth terminal on the lampholder to confirm. Ensure any threaded sections or joints are securely tightened.

Ghastly thing.

 

[andimac101]

Each to their own.. I guess. Better not reveal how much I paid for it then. If I needed to attach an earth to the inside of the body how would I go about it?

 

[sparkwright]

Each to their own.. I guess. Better not reveal how much I paid for it then. If I needed to attach an earth to the inside of the body how would I go about it?

Not sure, can't see enough of it.

If there are threaded sections which come apart you may be able to use a ring terminal crimp which could be clamped down with the locknut.

Don't know without seeing it properly.

Obviously you don't want to be drilling holes in it.

Can you visually see if all metal parts are in direct contact to each other?

Best check with a simple continuity check with a tester.

 

[andimac101]

There is a little rubber gromit in-between the shade and the stem so it wont be all connected. What if I soldered an earth crimp on the inside of the base would that do the job?

 

[sparkwright]

There is a little rubber gromit in-between the shade and the stem so it wont be all connected. What if I soldered an earth crimp on the inside of the base would that do the job?

But could it be connected by a metal threaded bar or some other metal fitting that you can't see?

You need to TEST, or get someone to test it for you.

 

[securespark]

Ghastly thing.

That's completely unnecessary.

 

[bernardgreen]

One option to make the lamp safe would be to use screened cable with the screen earthed and acting in a similar way as the armouring on SWA.

The cable would still need to be mains rated at 250 volts

The impedance of a copper braided screen would be more than adequate for use as a CPC to the lamp holders earth terminal.