I recently installed a circuit of 8x240v/50w halogen downlights opperated by a two way switch(one of which is on a bank of 6x2way switches) and protected by a B10 MCB. when I switched the circuit on for the first time it tripped the RCD....I checked the circuit but could find no problems with...
I would recommend W.B.P.ply of at least 25mm depth or better still 2x18mm screwed together at 150mm centres to prevent any movement of the floor which will result in cracked tiles .