Replacing Consumer Unit

Hi

Opinions required on the following:

An electrical company undertake associated electrical works for a new extension to a domestic property. As part of this work they install a new consumer unit. However, the new consumer unit has all final circuits protected by one common RCD.

I understand this is not compliant with the current edition of BS7671. The customer has not had any certification yet so I am not able to see if this non-compliance is noted. Is there anything to stop the contractor from selecting and installing this method of protection?

Thanks for your help

Whilst it's not ideal, it is compliant with current wiring regs.

Regulation 314.1 / 2

Subdivision of circuits to take into account danger arising from failure of a single circuit. In the example above, a main switch RCD covering all final circuits would cut power off to all circuits in the event of a single fault on a lighting circuit for example

Sorry I misread the OP as a new CU had been installed just for the extension circuits. If every circuit in the house is supplied from one common RCD then this is not compliant.

Does this consumer unit control whole house or just new ext circuits?, if ext, how many circuits.

RMS said:

the new consumer unit has all final circuits protected by one common RCD.

Click to expand...

Does the unit cover only the extension or the whole property.

As you have stated regulation 314.1, which would suggest that one RCD covering all the circuits of the installation would not be suitable, if a earth leakage fault occurred on one circuit as this would give complete power loss.
There is no reason in this day and age to be throwing units in that have one RCD protecting all circuits.
I would personally take issue up with the installer and gather their reasoning behind this and how they consider this to be compliant with the recommendations made within 314.1.

Regulations are not law but can be used in a court of law so it would be hard to force the issue.

The "314.1 Every installation shall be divided into circuits, as necessary, to:
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation." is the regulation is the bit we are talking about and with for example a caravan it is acceptable to have a single RCD covering whole installation however caravans have 12 vdc lights so bit before says:-
"(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit."

So if after fitting it trips all the time it does not comply but how can anyone at time of fitting know if it is going to trip so very hard to show it does not comply. However (iii) is more to the point my stairs are in centre of my house and with a power cut it does as a result give rise to danger or it would if I didn't have battery backed emergency lights over the stair well.

The idea of 2 RCD's is most rooms will have some lights powered from sockets so if a RCD fails the although main lights will fail the socket powered ones carry on working. As to if this complies is open to debate many feel the RCBO is the way to go. However there is a problem with RCBO's as they in a domestic consumer unit don't switch the neutral so with a TT supply you need a 100ma RCD feeding whole system then 30ma RCBO's feeding individual circuits.

With installations before 2008 with a TT system (means uses an earth rod) a single 100ma RCD was common. However any new sockets would need 30ma protection.

It is so easy to jump in with both feet and be unaware of some small detail like the single RCD being 100ma so yes I would complain but don't think you can force the issue.

The RCD 30mA covers the whole property, existing and new circuits.