My Lights Saga

[Jeff Gaines]

Round 2, the endoscope has arrived!

I have removed the light fitting in the kitchen and it has a chocolate block connector behind it presumably performing the function of a ceiling rose in connecting the lighting ring. The three spotlights are marked 240 v so presumably no transformer.

I have a live indication from a neon on the red cable and 66 volts across red and black when it is on, 0 when off (it's two way lighting).

There is an outdoor light as well (which also doesn't work) and a double gang switch by the back door, one for the kitchen light, the other for the outdoor light. Voltage at the connector is impacted by BOTH switches, that seems odd and I need to get my head round it.

I poked the endoscope up the hole where the chocolate block is and I can see white cables, fibre glass and the underside of the chipboard. I am having a bit of an issue orienting myself so I can understand what I can see.

I'm having a cup of tea while I think this through, particularly 66 volts....

[Andy Burns]

I can't remember if you said what type of meter you're measuring with?

Does one of the black wires have red sleeving?

I'd start by turning off power, mark all cables entering the chocblock, photograph it with the marks so you're sure you can put it back exactly as is, post us a link, separate all wires from the cables, temporarily terminate each wire into e.g. another length of chocblock with no connection between wires, measure voltage between red/black on each cable.

[Jeff Gaines]

Thanks Andy :-)

Will separate the block as next step.

In the meantime I looked at the outside light which fell apart in my hands. All the innards are now in the bin and I have connected the cables to a 20 Amp choc block and sealed the cover back on for now.

Not sure the meter has a known make but it's digital, could be 20 years old and reads 240 v when testing via my horribly hazardous plug, trailing lead and choc block setup!

[Brian Gaff]

Sounds like some are in series? Brian

[nothanks]

Until further info I suspect the apparent 66 volts is being induced on an open circuit wire. I would put a load on it (a bulb is simplest) and then measure the voltage - which I expect would be zero.

[John Rumm]

Digital meters present a very high impedance when testing voltage (i.e. the look like a very very high resistance load that draws only micro amps of current). In most cases this is a "good thing" - it means the meter has very little effect on the thing is is measuring. However in this case even a disconnected wire that runs close to another live wire will likely look "live" when measured just because it has an induced voltage on it, and the meter will see that due to the lack of load.

(Some DMMs designed with mains voltage measurements in mind (like the Fluke 117) have a low Z mode that deliberately introduces a small amount of load to the circuit under test to suppress any phantom voltage readings)

[John Rumm]

See my comment elsewhere in the thread.... Did you say that there was a two way switching arrangement on one of the lights? (If so then it is common to get a false voltage reading on one of the floating wires in the 3&E cable due to a long run in close proximity to other live wires in the same cable)

If you can get to all the wire ends then you could simply disconnect all of the terminations at the lamps (leaving those at the switches alone other that to check their terminations are tight). Them re-make them all from scratch, testing as you go. That way you can also sleeve wires appropriately as you go, so you have a better chance next time!

e.g.

With all the wires disconnected, it should be easy to find the one live set that is delivering power - so now you know which is the supply.

Your DMM on resistance/continuity mode will let you identify the switch wires as you toggle the switch.

Link wires between fittings you can identify by shorting L&N at one end, and testing for continuity at the other.

Yup a common problem with endoscopes IME!

[Animal]

means the cable's not connected to anything.

[Brian Gaff]

Depends how high impedance the meter is though. If shoving say a 100K resistor across the probes changes the 66v, then its either inductive or electrostatic pick up. Brian

[Animal]

it's a digital meter fool.