Is it a 9.5kw shower running on a 40amp mcb. If so maths are that its using 240v @ 9.5kw = 39.583 amps. Thats so very close the the 40 limit that your be on the breakers curve, and its quite likly that after some time it will trip.
a 9.5kw shower should really be on a 45amp , with 10mm cable.
Iforgot
March 2008