PATting touch lights

mark641 · Jul 13, 2021

One of my jobs is to PAT electrical goods for a local charity. Recently we have
been given some touch lights. On all of these, the switch interrupts Neutral
only and Live is on all the time. Is this normal or should I condemn these lights?
Thank you, Mark

littlespark · Jul 13, 2021

Are you saying there’s a live at the lampholder all the time?
Is polarity correct in the plug?

mark641 · Jul 18, 2021

littlespark said:
Are you saying there’s a live at the lampholder all the time?
Is polarity correct in the plug?

thank you for your reply, i will re-check.

Pete999 · Jul 18, 2021

mark641 said:
One of my jobs is to PAT electrical goods for a local charity. Recently we have
been given some touch lights. On all of these, the switch interrupts Neutral
only and Live is on all the time. Is this normal or should I condemn these lights?
Thank you, Mark

Us this by design, or has the lamp been connected correctly, L/N reversed?

mark641 · Jul 21, 2021

Pete999 said:
Us this by design, or has the lamp been connected correctly, L/N reversed?

I have re-checked. Polarity is correct at plug. Resistance from plug pin -- lamp socket pin:
live < 1 ohm, neutral > 2 MO. When plugged in with no bulb, the light pin is live.

brianmoooore · Jul 21, 2021

Is this a necessary part of the way these things work? Without an electrical field around them when they are off, how would they detect that you want to switch them on?

Pete999 · Jul 21, 2021

mark641 said:
I have re-checked. Polarity is correct at plug. Resistance from plug pin -- lamp socket pin:
live < 1 ohm, neutral > 2 MO. When plugged in with no bulb, the light pin is live.

Is it correct polarity at the socket outlet though?

brianmoooore · Jul 21, 2021

Pete999 said:
Is it correct polarity at the socket outlet though?

Hardly relevant to a PAT.

Pete999 · Jul 21, 2021

brianmoooore said:
Hardly relevant to a PAT.

Maybe but shows knowledge, and how long does it take to plug a socket tester in?

brianmoooore · Jul 21, 2021

The apparent reversed polarity has been shown up by the PAT tester, not by detecting a voltage on the lampholder when it's switched off.
The lamp would argumentably be safer if plugged into a socket was incorrectly wired.

static zap · Jul 22, 2021

My Ikea 3 step does have neutral to lamp holder continuity but happily works with polarity reversed . The 220V activate potential must be capacitivly derived .
..But Wired for neutral continuity , the activation surface shows Live to a volt stick , and does give a tingle !
(this is tech at its least clever)

mark641 · Jul 22, 2021

brianmoooore said:
Is this a necessary part of the way these things work? Without an electrical field around them when they are off, how would they detect that you want to switch them on?

Thank you for your reply. What I think should happen is: the base of the light should be energised at low voltage or via a large
resistor. When you touch it, a sub-lethal (I hope) current flows which the switch detects. (I am not going to try with wet hands.)
But I dont think the light pin should be live with < 1 ohm between it & the plug pin.

mark641 · Jul 30, 2021

Thank you for your replies. Polarity at socket was correct last time I tried, I will re-check. (We have had a new meter fitted ---
not by me). I dont think the COP says that PAs must be safe if plugged into a wrongly-wired socket.

Meanwhile, I have decided that these lights are definitely not safe.