All RCD installs

Because it still takes time for an RCD to trip.

 

What happens if the rcd malfunctions Mr C? - lets say a fault develops and the rcd is faulty..mcb trip time will then become highly relevant, and what kind of mcb trip time will occur in a no bonding situation?

 

Cos the big book says you do????!!!!!!!

 

To limit the potential under fault conditions.

 

Well up to 300ms before its classed as a failure, that 0.3 of a second, if the kettle casing is at 240 volts and the cold tap is at 0 volts thats full mains voltage through you until the RCD trips. If the water pipe is bonded then its 0 volts through you until it trips (assuming your not earthed anywhere else).

 

what if you're not touching the kettle and you just using the tap...or the outside tap

 

Well you will be ok, but its a good point about the outside tap, I've always said that an outside tap on a TNC-S system should have a plastic coupler on it.

 

Use a plastic kettle.