My 16th 10 way edition consumer unit has 4 MCB's fed from the !00A main switch(for lights, etc.) and 6 MCB's fed from a 80A, 30ma RCCD ( for power, shower, etc.). To update and comply with 17th edition regulations is it permitted to change the RCCD to a 100A,30ma RCCD to feed all 10 MCB's from the 100A RCCD by disconnecting the busbar feeding the existing 4 MCB's at present fed from the Main 100A switch and connecting it to the 100A 30ma RCCD. Then all circuits would be protected by a RCCD device.
There is not enough room in the box to fit in a 2nd RCCD as well.
The rules do not tell you how to do it just what has to be achieved and this includes:- (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.
With emergency lights installed the "Danger" due to loss of power is removed, but the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation is another question.
If after doing work it does not trip it's OK, but if it does then non compliant by this time it's a bit late. The normal method is to fit RCBO's instead of the MCB's on the non RCD protected section. However these are longer so will not fit all boards.
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