In uk.d-i-y, Timothy Hill wrote:
Hi,


[ ... tales of woe regarding apparently-correct wiring of PermLive,
SwitchedLive, N, and E snipped ... ]

There are too many things which could be causing your problem to make
a diagnosis-in-place possible (for exampule, your lighting circuit
might have its L & N reversed). Given that, I'd want to do more systematic
and separated fault-finding: so, disconnect the fan entirely, and satisfy
yourself that the lighting JB really has the voltages we expect, by
measuring voltages with respect to its earth terminal using a multimeter.
There should be NADI (near-as-damn-it) 0V on the neutral terminal (Black from
Circuit Cable + Black to Lights), though an all-electronic meter might show
a significantly higher fooled-you voltage through stray pickup from close-by
lives, which will disappear if you put even a 15W pygmy bulb or similar
tiny load across the alleged voltage. There should be 240V permanently on the
permanent live (your 'Red from Circ Cable & Switch Cable' terminal), and
NADI 0V on the switched live (Red from Cable To Lights & Black from Switch
Cable) when the lightswitch is Off, and 240V when the switch is On. (If you
don't get this pattern of behaviour, e.g. finding the black terminal is
240V permanently, your lighting circuit indeed has a L-N reversal somewhere
along the way - if you're "lucky" it's all the way back at the consumer
unit and all the lights are L-N swapped, more likely though is to find a
miswired JB or ceiling rose somewhere between CU and the end you're working
on. If no consistent voltage with ref to the E terminal, dodgy E in the
lighting circuit (not uncommon) - needs fixing first! then retest. And so
on...)

Having established that the supply side is OK, with the fan off the
wall/ceiling (on the 'bench', aka kitchen table ;-) you can then (paying
due care to safe working practices, i.e. at least use terminal strip
('chocolate block') connectors for your test wiring, not sort-of-twisted
together!) systematically test your fan: E to E, N to N stay in place; now
Live to its Perm-Live terminal only should leave the fan off, and then
a pulsed/switchable Live feed to its control terminal should make it
come on when the switch contact is made, and stay running for the preset
time after the control terminal Live is removed/switched off. If it
doesn't behave that way, you've shown beyond doubt that the fan is faulty,
and can take it back for a new one. (Test the new one on the 'bench' when
you get it, to keep Sod & Murphy off your back in the case of a fault with
the whole batch of fans your shop is supplying ;-)

HTH - Stefek