by ericmark »
Sat Feb 05, 2011 12:29 am
As to comply with 17th Edition nothing has changed to require that change.
Depending on DNO fuse size and MCB sizes it could be under rated but unlikely it would cause a problem.
Two main changes are with certain exceptions all circuits need RCD protection.
314.1 Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.
Really that has always been the case but now spelled out. There are three ways used to comply.
Using RCBO's
Using multi (2) RCD's
Emergency lights.
With existing installations easy to know if it complies. If the RCD does not regularly trip it complies even if only one. But with new only safe way is RCBO as one has no idea what will be used.
There is no requirement to up-grade however when for example fitting new sockets to a system that does not comply it is a pain to use Ali-tube cable and RCD sockets. (Ali-tube does not need RCD protection buried T&E does)
