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Old 28th Jul 2019, 6:17 pm   #1
Kalkanites
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Default Earthing vintage brass bankers desk light

Hello

I have acquired an old brass desk lamp which has two core wire using a brass bulb holder without an earthing connection.On stripping the light the two wires running throughout the lamp were unsheathed.I wish to replace the bulb holder with a replacement having an earth connection using three core wire.The bulb holder is screwed directly to the main body of the lamp which has a plastic switch to the base.Will this be sufficient or do I Also have to earth the lamp body also.
I have yet to establish if a thicker cable will run through the available space as it is quite restricted and wonder how others have overcome this
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Old 28th Jul 2019, 6:48 pm   #2
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Default Re: Earthing vintage brass bankers desk light

Does the bulb holder screw on to a metal nipple
to the body? If so one earth point will suffice.
You can test it with a test meter.
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Old 29th Jul 2019, 4:35 am   #3
Kalkanites
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Default Re: Earthing vintage brass bankers desk light

Thank you for your reply.

Yes the bulb holder has been adapted to take a steel thread which is screwed directly into the main body of the lamp. I intend to use the same thread on the replacement holder.
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Old 29th Jul 2019, 9:58 am   #4
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Default Re: Earthing vintage brass bankers desk light

If all metal parts of the lamp are in good electrical contact one earthing point suffices. (This can occasionally be a problem where different metals are involved and corrosion sets in)

Finding the smaller diameters of 3 core cable IS a problem these days- as is avoiding getting the ends twisted on final assembly.

Needless to say there are extra considerations if you are selling the lamp rather than keeping it.

Dave
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Old 29th Jul 2019, 10:10 am   #5
David G4EBT
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Default Re: Earthing vintage brass bankers desk light

A wise move to earth the brass body of the lamp.

You don't state whether the bulb-holder is an 'Edison Screw' ('ES') type or bayonet fitting, or whether it's a standard or small size. Standard sized holders have a half inch thread, 'SES' (Small Edison Screw) or small BC have a 10mm thread. As you say your lamp has a plastic switch built into it, no doubt your bulb-holder will be un-switched.

Most metal bulb-holders have an external earth terminal into which you thread the stripped end of the earth wire from inside the bulb-holder, like this one:

https://www.lampspares.co.uk/brass-b...iABEgKrvfD_BwE

Maybe that's the type that you have?

When screwed onto the lamp, provided the screw thread on the lamp body is clean, it should make good contact, but as has been said, if you check with a meter on the Ohms range with one test prod on the lamp body and the other one the bulb-holder, you should get the same reading as you would if you just shorted the two prods together. Some meters have a continuity setting, whereby if there is good continuity, the meter 'will beep'.

Some bulb-holder, like this one (which is switched, so not what your lamp needs) have an internal earth terminal:

https://www.amazon.co.uk/Switched-Ho...77728476&psc=1

Hope that's helpful.
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Old 29th Jul 2019, 12:18 pm   #6
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Default Re: Earthing vintage brass bankers desk light

take a good look around the switch area for an earth / grounding point
because as you describe 2 unsheathed wires going from the switch to the bulb holder it might be earthed at the base.
a picture of the switch area would be good
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Old 29th Jul 2019, 12:28 pm   #7
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Default Re: Earthing vintage brass bankers desk light

As BRASSBITS says, the lamp may well already be earthed inside the base.

Have you opened up the plug (assuming it has one) to see how many cores are present?
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Old 29th Jul 2019, 3:15 pm   #8
Kalkanites
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Default Re: Earthing vintage brass bankers desk light

Thank you for all your constructive replies

The brass bulb holder is a bayonet fitting small size 10mm thread without earthing point into which a threaded steel length has been inserted to screw into the light fitment which is a banker's light with brass shade. All metal parts are clean and in good contact. The lamp came without a plug and there are no signs of an earthing point having been used. There is however a bracket forming part of the lamp in the base which could be used to attach an earth cable.

This is my first attempt at rewiring an old lamp which I intend to keep so once again thank you for your interest

Malcolm
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Old 29th Jul 2019, 4:54 pm   #9
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Default Re: Earthing vintage brass bankers desk light

Please let us know how you get on, Malcolm!

I'm sure many of us are interested to find out what happens next. Projects like this are fun to do - and fun to read about
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Old 30th Jul 2019, 4:15 pm   #10
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Default Re: Earthing vintage brass bankers desk light

A good earth connection might be obtained using a 10mm soldered eyelet between the lampholder and the lamp body.
This would avoid having to get three cores into the lamp holder.
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Old 31st Jul 2019, 3:29 pm   #11
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Default Re: Earthing vintage brass bankers desk light

As expected it is proving impossible to insert three core flex within the restricted space throughout the lamp.Thank you Brigham for your excellent idea which could well work. Another suggestion is to use single chandelier wire which is 1.2mm and insulated in PTFE which I understand is much harder wearing than standard PVC therefore being safe to use in a metal lamp. Three lengths would be used which will measure less than standard 3 core insulated cable presumably the wires exiting the lamp would need to be taped.
I would appreciate your thoughts on this idea

Malcolm
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Old 31st Jul 2019, 6:52 pm   #12
The Philpott
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Default Re: Earthing vintage brass bankers desk light

PTFE insulated cable isn't flexible, if you put a bend in it the bend persists unless manually straightened. This is useful in some applications. (Don't solder PTFE insulated cable without good ventilation; above a certain temperature toxic fumes can be emitted.)

Overall i think i'd go with Brigham's idea.
Dave
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