Earthing the base of a metal standard lamp

[Msitekkie]

I have been asked to rewire an antique metal standard lamp. It has been rewired previously, but not earthed..! One of the screws on the base has a short length of uninsulated wire attached, presumably from the original earthing.

Unfortunately there is insufficient space to run an extra earth wire from the lamp holder down to the base, which seems to leave me with the option of breaking into the flex at the base and using some form of junction box although it’s difficult to imagine that’s how it was done originally & any junction box would need to be pretty small. As the lamp holder is only held to the (brass) fitting at the top of the lampstand by the tension of the cable, I am reluctant to rely on the lamp holder earth.
Can anyone advise please?

 

[westward10]

A picture might help.

 

[Msitekkie]

 

[westward10]

So are you saying the brass lamp holder is not secured to the lamp as in #1. The lamp holder must be fixed to prevent undue stress on terminations and possible access to conductors. The lamp holder looks quite old does it actually have an earth terminal.

 

[DPG]

So are you saying the brass lamp holder is not secured to the lamp as in #1. The lamp holder must be fixed to prevent undue stress on terminations and possible access to conductors.

Will make changing lamps tricky as well.

 

[mainline]

Change the lamp holder for one with an earth tag on it.

 

[davesparks]

If it is relying on tension in the cable to hold it together then something is obviously wrong as this is not safe.

As above, replace the lampholder with a brass one with earth terminal and fit it properly.

 

[westward10]

I think the base of the lamp holder is fixed now I look again but the lock ring is missing from the upper part hence the cable is holding it in place.

 

[Msitekkie]

So are you saying the brass lamp holder is not secured to the lamp as in #1. The lamp holder must be fixed to prevent undue stress on terminations and possible access to conductors. The lamp holder looks quite old does it actually have an earth terminal.

The earth terminal seems to be the v shaped piece at the bottom of the lamp holder that you can see with the screw in.

 

[Msitekkie]

Will make changing lamps tricky as well.

Seems to sit on fairly firmly over the rim of the piece below, not actually fixed but I had to tug the wires a bit to get it to move when I took it off & no movement when changing lamps.

 

[DPG]

Seems to sit on fairly firmly over the rim of the piece below, not actually fixed but I had to tug the wires a bit to get it to move when I took it off & no movement when changing lamps.

The trouble is that when someone us pulling and twisting the lamp they are stressing the connections. The holder needs to be fixed

 

[westward10]

The earth terminal seems to be the v shaped piece at the bottom of the lamp holder that you can see with the screw in.

The earth terminal is normally on the base part, is the lock ring missing. The whole thing needs replacing.

 

[Msitekkie]

If it is relying on tension in the cable to hold it together then something is obviously wrong as this is not safe.

As above, replace the lampholder with a brass one with earth terminal and fit it properly.

But what is the correct method to connect to that earthing point on the base? Or are you suggesting ignoring that & relying on contact between the components (there are a couple of decorative brass rings at the neck, then steel). I am not sure a new lamp holder could be fitted any more firmly, but maybe you know different, I haven't worked on many of these.

 

[Msitekkie]

The earth terminal is normally on the base part, is the lock ring missing. The whole thing needs replacing.

Yes, this seems to be an unusual way of attaching the earth, not one of those where you poke the earth through & secure it with a screw on the outside.
Looking online I see there are some brass lamp holders that appear to have a screw on a collar at the base - is this what you mean by a "lock ring" - that this can be tightened to attach it to the post of the lamp stand?

 

[westward10]

Can you show a picture of where the earth is connected. Yes the lock ring holds it all together.

 

[Msitekkie]

Can you show a picture of where the earth is connected. Yes the lock ring holds it all together.

I presume you mean the earthing on the lamp holder in the 2nd photo. As the one on the base is pretty clear. So I have attached another photo showing the V shaped plate removed, where I believe the earth wire would go.

The discussion has got a bit side-tracked on fixing/replacing the lamp holder & it turns out this does screw on - (it was firm but not screwed on when I removed it), so apologies for not being clear on that point.

So the discussion really comes back to where we started - do I need to earth to the point on the base & if so what is the correct (original?) method. Or do we rely on earthing continuity from the lamp-holder.

 

[DPG]

I think personally I would add an extra earth wire to join the nut/bolt on the base up to the lamp holder. Is there enough room to thread one through the upright pole?

 

[Msitekkie]

I think personally I would add an extra earth wire to join the nut/bolt on the base up to the lamp holder. Is there enough room to thread one through the upright pole?

No. That's what led to my original posting & the question mark over how it was attached originally.

 

[DPG]

No. That's what led to my original posting & the question mark over how it was attached originally.

Sorry, just realised it's 3 core up the stem already. I'll re-read the thread.

 

[Msitekkie]

I think personally I would add an extra earth wire to join the nut/bolt on the base up to the lamp holder. Is there enough room to thread one through the upright pole?

Actually revisiting that issue has set me thinking about using singles, although the cable still needs to be double insulated to the plug. So I wonder if I remove some of the outer insulation where the pole narrows higher up, effectively giving me singles where needed... I have some sleeved 1.5mm earth single (flex) that I might just squeeze through if I remove the insulation from the top section of that. I think it will still be tight though.

 

[westward10]

I presume you mean the earthing on the lamp holder in the 2nd photo. As the one on the base is pretty clear. So I have attached another photo showing the V shaped plate removed, where I believe the earth wire would go.

The discussion has got a bit side-tracked on fixing/replacing the lamp holder & it turns out this does screw on - (it was firm but not screwed on when I removed it), so apologies for not being clear on that point.

So the discussion really comes back to where we started - do I need to earth to the point on the base & if so what is the correct (original?) method. Or do we rely on earthing continuity from the lamp-holder.

I cannot see an earth terminal. I assume there is no locking ring, you really need a new lamp holder.

 

[davesparks]

As you have an insulated and sheathed cable running up to the lampholder then the earth only really needs to be connected at the lampholder.

Replace the lampholder with a new, complete, one and connect the earth.

 

[brianmoooore]

A modern switched brass lampholder will be almost identical in appearance to your existing one, costs very little, and will have an earth terminal attached to the base part. All that is needed is to replace the current lampholder and connect the earth wire in the flex to it, making sure that there is still slack in the earth wire if the live and neutral were pulled tight.
Keep the outer sheath on the flex all the way up into the lampholder.

 

[Msitekkie]

I cannot see an earth terminal. I assume there is no locking ring, you really need a new lamp holder.

Thanks for your continued feedback.
So I cannot see any other purpose for the V shaped plate to be screwed here, other than to hold the earth. The original piece of earth at the bottom is bare wire, so I am guessing it was laid along & held in place by the narrow part of the V when screwed down. Quite different to what we are used to these days. It's possible I am wrong though & the earth was just connected at the base.

With a new lamp holder I'm thinking I have the risk of the thread being different as it's an antique item? (Belonged to the customer's Grandmother).

 

[Msitekkie]

One approach I am considering, is adding an extra earth wire from the plug to the base & encasing this with the original flex in some braided sleeving.

 

[brianmoooore]

The thread in the base is likely to be close enough. Two standard sizes - 3/8" and 1/2".

 

[mainline]

There is only one way of doing it properly, as I said in #6

You will also have to ensure that the cable is secured in the lamp so can't easily be pulled out.

 

[davesparks]

One approach I am considering, is adding an extra earth wire from the plug to the base & encasing this with the original flex in some braided sleeving.

But the base doesn't need earthing, the lampholder does!

 

[davesparks]

With a new lamp holder I'm thinking I have the risk of the thread being different as it's an antique item?

Yes it will be almost certainly be different, you will need to use the appropriate imperial to metric adaptor.

 

[brianmoooore]

Yes it will be almost certainly be different, you will need to use the appropriate imperial to metric adaptor.

Rewired and replaced the lamp holders on several multi lamp old chandeliers over the years, and as far as I can recall, I've never had to use an adaptor, other than 3/8" to 1/2" occasionally.

 

[Msitekkie]

But the base doesn't need earthing, the lampholder does!

Struggling with that, as the original earth appears to have been connected to the base (does that count as "manufacturers instructions"? ) & Some here suggesting there is no earth connection on the original lamp holder.
Let's say for arguments sake the cable became frayed at the base of the lamp holder from the cable being moved about & the body of the lamp became live, are we still relying on the earth to the lamp-holder?
I should possibly mention here that the core of the lamp is also telescopic.

 

[westward10]

What was done in the past is neither here nor there. You need a new lamp holder which incorporates an earth terminal, a lamp holder which will fit securely to the existing thread.

 

[davesparks]

Struggling with that, as the original earth appears to have been connected to the base (does that count as "manufacturers instructions"? ) & Some here suggesting there is no earth connection on the original lamp holder.
Let's say for arguments sake the cable became frayed at the base of the lamp holder from the cable being moved about & the body of the lamp became live, are we still relying on the earth to the lamp-holder?
I should possibly mention here that the core of the lamp is also telescopic.

It doesn't matter where the original earth was connected, the original cable and connections are obviously long gone and how it was done will forever be a mystery.

As you are rewiring this you are taking responsibility of manufacturer for this.

The metal base etc contains an insulated and sheathed cable, the only part of the lamp which contains single insulated conductors is the lampholder. Therfore the part which needs to be earthed is the lampholder.
The rest of the metal parts will obviously have a connection to earth via the lampholder being screwed onto it.

If the cable becomes frayed in any normal and foreseeable use of the lamp then you have failed to secure it or protect it correctly.

 

[Msitekkie]

What was done in the past is neither here nor there. You need a new lamp holder which incorporates an earth terminal, a lamp holder which will fit securely to the existing thread.

OK. What

It doesn't matter where the original earth was connected, the original cable and connections are obviously long gone and how it was done will forever be a mystery.

As you are rewiring this you are taking responsibility of manufacturer for this.

The metal base etc contains an insulated and sheathed cable, the only part of the lamp which contains single insulated conductors is the lampholder. Therfore the part which needs to be earthed is the lampholder.
The rest of the metal parts will obviously have a connection to earth via the lampholder being screwed onto it.

If the cable becomes frayed in any normal and foreseeable use of the lamp then you have failed to secure it or protect it correctly.

OK. Thanks for that. I will do as suggested & PAT test the earth resistance at the base. Hopefully OK. Just a little concerned about the number of moving parts between lamp holder & base (screw on brass ring plus telescopic pieces, that might potentially get oiled) & how much resistance this might introduce. I think the telescopic bits are brass (are on the outside anyway), so hopefully not liable to corrosion.

 

[westward10]

It is only the brass lamp holder which needs to be earthed. If the cord is installed correctly and correctly protected/restrained where it enters the lamp it is fine.

 

[Msitekkie]

It is only the brass lamp holder which needs to be earthed. If the cord is installed correctly and correctly protected/restrained where it enters the lamp it is fine.

OK.Thanks for that reassurance.