Voltage through earth to desk

[Fergus Macdonald]

I built a metal desk with wood top. I just wired in a 500W heat lamp on the desk.

13A plug goes to a single metalclad socket via 1.5mm2 3 core cable.
Same cable then goes from socket to 1 way metalclad switch.
Same cable then goes from switch to heat lamp.

Earths are all connected to each other and to back boxes.

When I take my multimeter and measure between the socket screw and the metal desk I get about 10V. When I turn the heat lamp on it reads about 25V.

Is that normal? Is that something to be worried about? Metal desk is not earthed.

Thanks in advance.

 

[Fergus Macdonald]

Interesting. I wondered about doing that before posting this but thought I better check out the voltage reading. Wouldn't be too hard to do and might mitigate an issue then no harm in doing it.

 

[Midwest]

No No No. As said, if its not exposed conductive part or extraneous conductive part, bonding something can only make something more dangerous than it actually needs to be.

 

[Midwest]

One simple option would be to run an earth from your socket extension built into the desk to the metal frame.

Why?

 

[Wilko]

Hi - if you want another cheeky check - grab a 10k resistor and put it across your meter terminals, then try to measure your 10v again.

 

[Pat H]

Why?

For peace of mind. The OP was troubled enough to measure and find a voltage (a minimal ghost voltage at that)
The desk has the extended socket installed so an earth is easily available. Use that and any ghost voltage will be gone and peace of mind is restored.

 

[Midwest]

For peace of mind. The OP was troubled enough to measure and find a voltage (a minimal ghost voltage at that)
The desk has the extended socket installed so an earth is easily available. Use that and any ghost voltage will be gone and peace of mind is restored.

I'm not sure BS7671 was compiled for peace of mind.

This desk, from the description given, is not an exposed conductive part, therefore does not require 'Earthing'.
If it requires 'Bonding', would depend on whether it is an extraneous conductive part, which would require testing to which Lucien referred to in #8. Not using a voltage checker.

Bonding something, which is not an extraneous conductive part can, in certain circumstances make the situation more dangerous by distributing further any touch voltage, e.g. bonding internal metal cable tray used by MI cables.

If the advice is to bond the metal desk, then this would have to extend to any metal sinks, metal baths, metal radiators, metal windows etc. Thankfully, something resigned to the past of the 15th edition.

 

[Pat H]

Indeed the other option is to do nothing.

 

[Midwest]

The only option, is to apply the regulations of the latest amendment of BS7671 to a new electrical installation, not a previous edition or amendment.

 

[Barry White]

Hi Fergus since you mentioned you had lost the earth recently in another part of the house. I advise you to call the electrician back for a quick check. This will give you peace of mind.
I advise this as there is a slim chance you have a break in the earth continuity to the socket in the office and the capacitive voltage may actually be on the socket. Not the desk.

 

[DPG]

One simple option would be to run an earth from your socket extension built into the desk to the metal frame.

No offence intended, but this is the sort of thinking that can lead to dangerous situations. Connecting things to the electrical system 'to be on the safe' side is NOT a reg. Daz

 

[Fergus Macdonald]

Thanks for all the help and advice guys, really appreciate it. Will leave the desk unearthed. Fairly confident my wiring is good but was surprised about the ghost voltage as wasn't aware of such a thing.

RE sockets in my house, we've had those checked and fixed thankfully.

 

[davesparks]

One simple option would be to run an earth from your socket extension built into the desk to the metal frame.

To ensure that it is more likely to become dangerous in fault conditions than it is now???