MCB tripping

[quackers]

Hi Guys

First time Ive posted , I am stuck and just wondered if anyone has an idea of what I am seeing.
Basically I have a customer (New House 4 years old) that is tripping the lights upstairs.
IR checks out and is as would be expected on a house that old. Zs is exactly the same as the original Installation Certificate.
The house has two bedrooms, one en-suite and one family bathroom.
All switches are unmolested-everything has been left as the builders left it four years ago.
All the lights upstairs are of the low voltage downlights 50W Halogen --God I hate them !!
The lights are on a 6 A Mk breaker. I have replaced the breaker as everything checks out.
However the lights still trip. On or off makes no difference, give it 20 mins and they trip.
All bathroom lights are correct in the zones-no damp.
However there is one dimmer in the bedroom. Have any of you guys come across a dimmer pulling down a 6 A MCB when off ??

Any help or direction greatly appreciated.
Cheers Steve.

 

[bugsy]

Is the mcb or RCD tripping?

 

[Graeme Harrold]

HAve you got a clamp meter? Find out what is flowing

 

[bugsy]

Is there a fan on that circuit?

 

[quackers]

Hi fellas thanks for the response. - The MCB is tripping Not RCD- Nope dont have clamp meter but calcualtion should draw 3.76A- so way below the 6. Was tempted to add a 10 but do not want to mask the fault

 

[quackers]

Thanks Bugsy yes there are two fans one in each bathroom but have been isolated

 

[BertUK]

could it be a faulty transformer if they are low voltage?

 

[robsparky1975]

just to check,when you did IR tests,did you test the switch wires to eliminate from being at fault.

 

[bugsy]

have you had a look at the trannies , not getting too hot?

 

[quackers]

Hi Bert yeah I thouht about that , but do you know if there is a way to test the transformers easily. Theres quite a few upstairs I guess the builders had a job lot !!

 

[quackers]

Thanks guys for replying so quick. Yes have checked switch drops and all check out. Even two way switching to downstairs , strappers OK.
Have not held onto the transformers to check for heat- any idea of how warm they should be ?

 

[bugsy]

stick a nulti meter on them but as it also happens whrn their switched off it's a long shot, have changed the dimmer for a plate switch just to eliminate it?

 

[quackers]

The thing that is puzzling me is when I did the IR tests the Dimmer was removed from circuit. Might try a different switch non dimmer and reenergise

 

[saveloy]

Have you checked for a signal booster in the loft wired off lighting circuit?

 

[quackers]

Thanks Bugsy , read my mind. Thats what I think I may have to do. I mean its a newish house everything is really good , wiring really good a credit to whoever installed it , but downlights I hate they get hot and in my view blooming dangerous- especially when they sell them to jo-public !!