I've got an old Manrose XF100S extractor fan which could do with replacing, and I was thinking of upgrading to the one containing a timer. The feed appears to be standard UK three core and earth as the wires are brown, black and grey, though the outer casing finishes up in the ceiling somewhere and isn't visible (as a side note I'm not sure at this stage what's going on with the earths as there appear to be three of them all going into one side of a connector block, was only expecting one...)

The current wires being used are the black and grey, which must be switched live and neutral, so I was assuming brown would be a permanent live, provided for future use should it ever be needed. This currently terminates into a separate connector block with nothing in the other side. I wanted to confirm what all the wires are before buying a new fan, so have tested them with my multimeter but got some unexpected results.

With the isolator, lights and fan on:

  • Black-Earth is around 230v, so confirmed this is live
  • Grey-Earth is 0v, so confirmed this is neutral
  • Black-Grey is around 300v, wasn't expecting this, thought it should have been 230v again?
  • Brown-Earth is around 100v, again was expecting 230v
  • Brown-Black/Brown-Grey are both around 50v

With the isolator on but lights off, everything is 0v

So really my questions are:

  1. I've just read about phantom voltage, could it be that the brown wire isn't actually attached to anything on the source side (ie at the isolator), but when the lights/fan are on my meter is picking this up as either 50v or 100v depending on what I check it against? I'd rather not remove the isolator at this stage to look behind it, the edges have been painted onto so will ruin the wall finish if I unscrew it.
  2. Why does live-neutral give a reading of around 300v?
  3. Why might be three separate earths coming into the fan area? I might figure this out myself if/when I remove the fan and can see where they go, but at the moment it's a mystery!
  • Does your house receive single-phase or 2-3 phase service? Aug 16, 2022 at 1:23
  • Single-phase. Might also be worth pointing out a second bathroom already has a timer fan with the same, at least visually, isolator which is all working fine. Aug 16, 2022 at 8:07


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