No commentary on protective devices would be complete without reference to residual current devices. The IEE Regulations specify that, provided the required disconnection times can be met for circuits and all bonding is in place, fuses and/or CBs will provide the necessary protection against electric shock. RCDs are only required

• when disconnection times cannot be met
• when they are needed as supplementary protection against direct contact
• for all socket-outlet circuits in TT systems (they are also preferred for other circuits, but overcurrent devices are acceptable)
• for socket-outlet circuits from which it may be reasonably expected that portable appliances may be supplied for use outside the main equipotential zone
• for certain circuits in both rooms