I have searched Google, but get bombarded with "RCD" type answers. I read a few answers here that may have been relevant but turned out not to be, so I post my question. Being my first, I may unintentionally break some rules – hopefully not.
I was about to make a change to a domestic light circuit so tested the light socket to ensure the circuit was dead and I had pulled the correct fuse. (Yes this circuit is 50-60 years old, hence no CB!) What I discovered with the digital multimeter (set to 700V AC, as nearest higher setting) was that 33 AC volts existed whichever direction I connected the leads. And this is with the correct fuse removed!
Wanting to be more certain I used a light bulb to verify more digitally – i.e. 0 or 1.
I proceeded with the task which used the existing light wires as pull leads to get another cable down the wall. All finished I was set to reconnect the circuit exactly as before.
My understanding was that the Live wire went to the Common connection on the switch, so I reconnected the fuse and tested for the live wire with a neon single-connecton screwdriver and connected the one that 'glowed' to the Common terminal of the switch and the other to terminal 1.
At some point; either reconnection of the fuse or flipping the switch, the fuse blew. I have not replaced it, until I get to the bottom of this problem. So my questions are;
1 – first, does the live wire go to the common terminal on a two-way switch? (being used as 1-way currently, but hopefully soon to be two way).
2 – Has the neon screwdriver led me astray for which was the live wire?
3 – Is it possible that my house has neutral switching and if so, how do I find out? It has been illegal here in NZ for at least 60 years I would have thought. If neutral switching should I put the other wire to Common and the live one to terminal 1?
4 – Is 33 volts AC a concern when the circuit is off? I did not get any form of tingle when man-handling the wires. We have 240 V AC circuits in NZ for domestic wiring.
Thank you for any answers that you care to provide.
Best Answer
It is normal for a typical multimeter to show some low voltage on disconnected wires. This comes from the capacitance and inductance of the wires themselves.
Since there is essentially no load (the meter puts a tiny insiginificant load on it) that voltage doesnt go away. But the actual current it could supply is tiny. It poses no safety hazard and can't shock you.
Some meters have a mode that puts a load on the circuit to eliminate such false readings. If yours doesn't the easiest thing to do is measure while a load like a lightbulb is still connected.