shock from a light stand

Albert · 30 Mar 2009

A metal stand alone lighting unit, double insulated, connected with plug to a socket. The user complained that some one had a shock when tried to change the bulb. To make a long story short; I checked the continuity of earth in the sockets and insulation, there is no problem with the sockets circuit.

I measured the voltage between the stand and earth it was 11.4V.

What do you think? what would you do?

RF Lighting · 30 Mar 2009

Is it an ES lampholder?

sm1thson · 30 Mar 2009

have them describe the shock, could it have been static?

Albert · 30 Mar 2009

RF Lighting said:
Is it an ES lampholder?

Yes

securespark · 30 Mar 2009

Slight breakdown somwhere, Albert.

Albert · 30 Mar 2009

sm1thson said:
have them describe the shock, could it have been static?

They said that they did not know what kind of bulb goes there, I think that some one touched the live in the housing while trying to find out the type of bulb needed.

BTW; for reference I measured another light fitting, the same type, and it read 3.5V, a more modern one read 0.1V.

I wonder what voltage will be considered as safe, if at all.

Albert · 30 Mar 2009

securespark said:
Slight breakdown somewhere, Albert.

I thought so, and recommended them to change this unit, but it is still bugs me.

Taylortwocities · 30 Mar 2009

Daft to change the lamp with it plugged in...
Did you check that the neutral is on the screwed part of the E27? If the connection in the plug (or in the socket!) is reversed then the switch will be in the neutral leg leaving the screwed part live even if the lamps switch is off.

Albert · 31 Mar 2009

Taylortwocities said:
Daft to change the lamp with it plugged in...

Told them

Did you check that the neutral is on the screwed part of the E27?

Still the stand should not be live, it is double insulated...

If the connection in the plug (or in the socket!) is reversed then the switch will be in the neutral leg leaving the screwed part live even if the lamps switch is off.

Checked it, it is ok

holmslaw · 31 Mar 2009

BS3036 · 31 Mar 2009

Albert said:
I measured the voltage between the stand and earth it was 11.4V.

What with? A multimeter?

Albert · 31 Mar 2009

BS3036 said:
Albert said:

I measured the voltage between the stand and earth it was 11.4V.

Click to expand...

What with? A multimeter?

What would you measure it with?

bernardgreen · 31 Mar 2009

Measure it with a multimeter AND a simulated load.

Meauring the voltage on a floating ( ie not earthed ) piece of metal that is surrounding live wires will give a voltage due to the capacitive coupling between wire and metal. The voltage may be seen as high but the amount of energy "under" that voltage is very small ( provided the insulation is good ) The voltage measured with a high impedance meter will therefore show as being high. It is high as the meter is not taking any significant energy in the form of current. Measure it with something that does take energy ( low impedence meter or with a lamp or resistor across the leads of a high impedance meter ) and the voltage will be next to zero. If it isn't then there is a fault with the insulation.

Albert · 31 Mar 2009

bernardgreen said:
Measure it with a multimeter AND a simulated load.

Meauring the voltage on a floating ( ie not earthed ) piece of metal that is surrounding live wires will give a voltage due to the capacitive coupling between wire and metal. The voltage may be seen as high but the amount of energy "under" that voltage is very small ( provided the insulation is good ) The voltage measured with a high impedance meter will therefore show as being high. It is high as the meter is not taking any significant energy in the form of current. Measure it with something that does take energy ( low impedence meter or with a lamp or resistor across the leads of a high impedance meter ) and the voltage will be next to zero. If it isn't then there is a fault with the insulation.

Thanks, this is interesting, I measured it with a fluk 1653, normally I use it for test and inspection (EIC and PIR).

I think that it will give a relaible reading, as well as the other 2 units gave a different reading. I suspect that this unit is faulty.

bernardgreen · 31 Mar 2009

There is probably an "official" value for the resistance of a simulated load but I use a 270,000 ohm resistor ( 270KΩ ) ½ Watt between metal and earth for the initial check. This is "safe" as if there is a short ( Live to the metal ) then the resulting 230 volts across 270KΩ is less than 0.2 watt so the resistor doesn't explode.

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shock from a light stand

holmslaw

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