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13
Protection
against
electric shock
Protection against electric shock needs to be
provided by offering both basic protection and
fault protection.
Basic protection includes the insulation of live parts and barriers
or enclosures such as distribution boards. Appropriate devices or
blanks must be fitted to maintain IP2X or IPXXB. If the top of the
horizontal surface is readily accessible then the level of protection
there should be IP4X or IPXXD.
Automatic disconnection of supply will usually provide fault
protection. This involves protective earthing, protective
equipotential bonding and the automatic disconnection of a
device if there is an earth fault. The designer will normally need
to ensure co-ordination of protective devices and earth fault loop
impedances so that disconnection will occur within the maximum
times given in 411.3.2.2, 411.3.2.3 or 411.3.2.4.
An additional requirement for the protection against electric
shock is to specify RCDs where they are needed. 415.1.1
recognises that RCDs with a rated residual operating current
(I∆n) up to 30mA and an operating time not exceeding 40ms
at a residual current of 5 I∆n provides additional protection
for ac systems if the basic or fault protection fails, or against
carelessness by the end user.