Permanent live not permanently live!

[walders]

Hi, this is my first post - please bear with me. I've searched around, but can't find an answer to this...

I am replacing an extractor fan above our bathroom. It seemed so easy. the old fan had 3 wires coming in: black, brown, grey (switched live, permanent live, neutral, respectively).

I thought I ought to check this before wiring in the new fan, but the results confuse me...

With the black terminal of my multimeter connected to the grey (neutral), and the switch off, the brown is 200V, and the switched live is 50V.
with the switch on, the brown is 0V and the black is 240V.

Indeed, if I wire up the fan according to the instructions (it's a Vortice lineo 100 with timer), the lights glow when the switch is off (50Volts worth), and the fan is on (I assume it's the overrun timer). When I turn the switch off, the fan turns off (0V in the perm live) and the lights are on (240V in the switched live).

I assume something is wrong further back? There is a junction box that these wires came from. Any help welcome!

Walders

 

[ericmark]

Are you sure grey is neutral and not black.

The colours Brown, Black, and Grey are assigned to three phase equipment and all are line colours. Where the cable is used for a single phase supply it is up to person fitting the cable to sleeve it with correct colours.

The 17th Edition table 7E shows the use of Black as neutral with DC supply and to prevent confusion many also use Black as neutral with AC as well.
However since Grey replaced Blue and on single phase flex blue was neutral some people use grey as neutral.

There is no right and wrong on use of colours all the regulations say on single phase it should be Brown for Line (Phase) and any other colour (other than green/yellow) may be suitably marked i.e. sleeves fitted to show it is Line voltage.

 

[bernardgreen]

Use the earth as the reference point for the meter

One wire will be permanently at 230 v AC...... Permanent Live

One wire will be permanently close to 0 v AC ..... Neutral

One wire will be at 230 with switch on and something lower with the switch off ..... Switched live. ( the "off" voltage would be almost zero if there is a filament lamp in place. Other lamps or no lamp will allow capacitive coupling to induce a voltage on the switched live wire.

Once identified sleeve the wires and keep a note of the colours used for future reference in or near the CU.

 

[walders]

Thanks for your replies. I was struggling to find a reliable earth - the earth cable in the flex had been cut right back, so there was no access to it without stripping back some of the sheath.

The black was indeed neutral, with grey as switched live. That surprised me, I hadn't realised there were different traditions. The light wires were brown & blue, so they weren't just keeping black as the consistent neutral.

I'm sure these arguments and discussions around colouring could go on for ever. The bottom line is that I now have a working fan, and have learnt a little about wire colour traditions!

Many thanks!

Walders