MCB triops every 20, 30 mins.

[Npt88]

Probs wont help you too much but i had the same fault on a med centre the other week tripping randomly anything from 5 mins to 5 hours. Bunch Tested circuit, clear. Replaced mcb, Same. Dissconnected all lights tested again, clear. Eventually what i fouind it to be was when it had been installed at least 15 years ago in galv pipe and singles they used ceramic connector in a through box then into the fitting in flex. and it was a line single trapped between ceramic block and through box and over the years with heat etc it had blown apart and then obv tracking across at random times and tripping! Took me 9 hours to find this bugger! Had a well deserved pint that night!

 

[sedgy34]

Split the circuit mate and try it it might give you a bit of a clue

 

[grandfortune]

ok guys, thanks for your help and reply's,, it was a steel beam put down for the loft bedroom, it was trapping the cable, had to take the landing ceiling down to find it, two days labour x2 men down, but glad ive found it as its a weight off my mind.

Cheers
Grand

 

[Brightspark2]

What were your IR results between Line & Neutral.

And if clear have you tried keeping the test on for a least 1 minute to see if it drops?

Some test instruments dont like that, cycle time of about 20-30 seconds on IR tests.