Is a Lamp Socket Safe Without an Earth Cable?


Postby mth » Sun Jun 11, 2017 1:25 pm

Hi all,

I have posted month ago a question about how to make a lamp without earth cable safe (by adding one). The answer somewhat boiled down to getting a professional to do it, so that I don't end up electrocuted because of a sloppy job.
Before I get an electrician in to fix it and pay more than the lamp is worth, I just want to make sure if I am not on the wrong path altogether:

The lamp shade is entirely metal and just fixed with a bolt/ nut to the bulb socket. The socket itself is plastic and has the bolt screwed in:
https://drive.google.com/file/d/0B5hJCFfDddTSc1BuTDhIbGp2d2c/view?usp=sharing

Now the facts that make me think:
- the lamp is an import from the US, so not necessarily complying to EU safety standards
- the bulb socket is made in Italy, from plastic, but the threading that holds the bolt is metal
- The socket is plastic, so should be safe, but the connection via socket -> threading -> bolt -> shade could be a risk?

What is the easiest / least costly way to figure out if this lamp is designed to be safe without an earth connection?

Many thanks
mth
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Postby ericmark » Mon Jun 12, 2017 6:38 am

We have type testing, so one lamp is tested to destruction and in view of that the design is accepted or rejected, so you can have a metal lamp without an earth cable which is considered safe, this is common for touch control lamps, which are normally metal and rarely have an earth.

We also refer to double insulated, often you find a metal lamp where there is a plastic sleeve inside the metal and the cable is within that plastic sleeve.

However for a home made lamp all we can do is an insulation test, some PAT testing machines have a wand to test repaired items of class II design, the worry when repairing a drill for example is a screw could be too long and so too close to the live parts, so the live parts and wand have around 2500 volt between them and every screw is touched with the wand, it is considered if the 2500 volt does not get through then you are safe with 230 volt, it is only done after a rebuild as 2500 volt can also damage items and many new PAT testing machines no longer have this option as so many items were damaged by the test.

So in your case it is now to design and use of plastic pipes inside the metal pipes to ensure there is no possible chance of a fault in future, all the electrician can do to test is use 2500 volt if his tester allows its use, and any cable which is flexed in use can still cause problems although unlikely.

When doing PAT testing I have many time taken items out of service simply because there was no sticker saying they were safe, often I would tell people, take it home, nothing really wrong with it, but I can't pass it for office use.

So you are in the same position, you use grommets, and sleeves where you can and design it so risk is at a minimum, but it can never really be classed as class II it can never have the double square sticker fixed on it. It does not really matter if you build it or an electrician it is just down to good design.
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Postby mth » Mon Jun 12, 2017 8:52 am

Hello Erikmark,

many thanks for your reply. I am not sure if I made my intention very clear, I don't want to tinker with the lamp-socket in any way myself (I don't think I am qualified enough). That was my learning from the last post I made in this forum.

So I see two choices:
1. Figure out/ proof that the socket is already safe and doesn't need an earth connection. I take from you that I can't get around a PAT test to be sure. (I also wrote to the merchant, but he basically replied that I should do as I please)

2. I buy a new socket that allows an earth cable to be attached and has magically the exact threading hole that I need to put the lamp shade on.
mth
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