Being an urban house basher i don't often come across a TT system. Now we have the 17th how does that affect the RCD on a TT system. It used to be a 100mA rcd covering the whole dwelling. What with dual rcd board and RCDs with a 30mA rating, which RCDs do you fit? I don't see any point in fitting the 100mA RCD if I've got the two 30mA, is that right?