Tricky Lighting Fault?

[brs73]

hello chaps
i've got a fault on a lighting circuit in a purpose built flat. concrete floors and ceilings with a false ceiling in the bathroom and bedroom which have downlights.
when the bathroom downlights have been on for a couple of minutes they start to dim slightly on and off like they aren't getting enough power.
this also happens to the fan. this carries on happening until the lights are switched off.
i have seen this before whilst working on sites when people have switched on large items of plant and all of the lights dim.
the customer says that her children get scared because they think they have a ghost.!!
the bathroom and bedroom are supplied from the same circuit and the bedrom is not experiencing any problems.
there are 8x 50w 12v downlights in the bathroom with a 12v 100mm extract fan
i can see, but i cannot access the junction that has been made to incorporate the downlights above the false ceiling from the original lighting position
so far i have:

replaced the 400w dimmer to the bathroom with a 1000w dummy dimmer.
isolated the bedroom from the circuit and had the bathroom running on its own.
removed the fan from the circuit.
fed the bathroom from another source.

none of this has made any difference and i am frankly a bit baffled as to why this would happen.

any help would be appreciated
thanks in advance and merry xmas everybody

 

[gutterball]

transformer??? they overheat and cut off then come back when cool. but this usually takes a while.

 

[Flying Ninja]

Are they all fed from single transformer, Does the fan have it's own transformer? Only option may be a 4" hole saw to access it.

 

[brs73]

All fittings and the fan have individual transformers

 

[Richard Burns]

Have you checked the pins on the lamps, I have found them to be prone to corrosion, paticularly in bathrooms, if they are connected through the corrosion and get hot they may be sealing themselves off which dims them.

Try taking some lamps out and see if the problem resolves, this may allow you to narrow down the fault

Alternatively there may be a near short occurring that is just jumping across on (probably) the fitting or fitting to transformer connection that is drawing power.

 

[Flying Ninja]

Hmm not an easy one....Sounds like you have to locate the joint at the original lighting position as this will be the only point other than the sw that the fault could be arising as you said you have checked the supply. Good luck and keep us posted as it is an interesting one.

 

[brs73]

well i'm going there today.
i'm gonna try changing some lamps and transformers first and if not i;ll be cutting a lovely new hole into the ceiling.
i will give an update later
thanks