Shower fault...

[SSE]

New shower put in 9500 kw, 45 amp mcb as didn't have 40 on me & installed in 10mm cable. As soon as i pushed the power button on the shower the rcd tripped (it's an old hager board with one of those combined rcd/main switches) Everything is connected correctly, and before I pushed the power button I took a reading at the shower switch (supply side) and got 240v. Never got the chance to take a reading in the shower as I couldn't get in then due to other workers! Any ideas?

 

[SSE]

Ok. Update guys. Was back at the job today, flicked breaker back on and suprisingly it worked without tripping the rcd. Bit puzzled as done nothin' different from last time? Only thing i can think of is the suggestion that somebody had on friday concerning dampness as the cover had been left off. Thanks for takin' time out to reply anyway.