In my hall, below the loft access hatch, there is a DP switch with an integral neon light. It was there when I bought the house. The switch allowed the previous owner to switch on the loft lights and the neon light reminded him (now me) that the loft lights are on if the hatch is closed. Its quite a clever little system. However, I was intrigued how it is wired up, so I had a look behind the switch. There is a single 1.0 m2 T&E cable (old colours), with the red wire connected to "live - In". The "live - out" is connected to the black wire (with a red sleeve; switched live) plus one of the wires for the neon. The other wire for the neon is connected to the CPC terminal which in turn is connected to the CPC in the cable. The cable is connected to the lighting circuit for the rooms below.

Clearly, the neon works because current passes through it to earth.

My understanding of the CPC system is that the CPC is at equal potential throughout the house, so why don't I get a shock when I handle the CPC (anywhere in the house) while the loft lights are on?

I suspect that if an RCD was connected to the lights circuit that it would trip when the loft lights are switched on.

Thanks
Kev

emm im pretty sure the neon is prewired off the outcoming feed, with the guts of the neon pre wired, have you got a pic?

The neon will still work connected to the CPC as the current required to make it 'strike' is measured in microamps - far below anything you can possibly feel (or activate RCDs). Most neon have a series resistor of (at least) 1 megohm as well.

_________________
This post may contain nuts

Here it is. Its a little fuzzy due to the limitations of my camera phone. The neon is at centre of the assembly with the wires permanently connected (pre-wired, as you say). The CPC is connected to the Neutral Out and the usual terminal on the back plate. In case your wondering why the RH screw is fitted upside down, it doesn't have a retaining washer so I temporarily hung it upside down through the hole to prevent loss.

Anyway, it works. Its a good warning against leaving the loft lights on or accidentally switching them on with the hatch closed.

Kev