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Can I add RCBOs to a dual RCD board under a TN-S system?

Emmanuel Yohannes

Hi I'm an not an electrician, but a Level 2 Electrical Installations student with not alot of electrical knowledge. A relative is getting her kitchen re-wired and two consumer unit changes will be required. I have two problems

There are two consumer units. The first one has 2 double pole 63A/30mA RCDs protecting 5 MCB's each with the smoke alarm on one of the MCBs. The second consumer unit is smaller with just one 80A/30mA RCCB protecting 4 MCBs

A different electrician from the one doing the job performed the EICR on his report and pointed out with a C3 code that the 'smoke detectors are not a separate rcbo'. and 'No surge protection has been provided'.

So, would we be able to add just a single RCBO for the smoke detector and put it into the dual RCD board or would changing the dual RCD CU to a 10 rcbos suffice? Also, do I have to buy surge protectors for both consumer units or just the larger one, cause the smaller CU is only protecting the kitchen lighting and ground/first floor lighting because I thought surge protectors would only apply for socket circuits.

Sorry for the long description, but this is an urgent matter and any help will be appreciated. Images of both large and small CU are below

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    1. There is no requirement for separate RCD protection for the smoke alarms. Opinions differ - the counter-argument is that if the alarms are fed from a lighting circuit, it becomes obvious that they have lost power when the lights fail to come on. In my opinion C3 is not justified, but C3 alone does not require immediate action.

    2. As from Amd 2, surge protection will be required, but you have until 26 Sep 22 to install to Amd 1.

    3. I don't see any obvious reason to change the consumer units - they appear to be in good condition. It is not necessary to upgrade every time that a new edition or amendment to BS 7671 is published. What should be done, however, is to ensure that the new work complies with the current edition and right now AMd 1 and Amd 2 are both current.

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    1. There is no requirement for separate RCD protection for the smoke alarms. Opinions differ - the counter-argument is that if the alarms are fed from a lighting circuit, it becomes obvious that they have lost power when the lights fail to come on. In my opinion C3 is not justified, but C3 alone does not require immediate action.

    2. As from Amd 2, surge protection will be required, but you have until 26 Sep 22 to install to Amd 1.

    3. I don't see any obvious reason to change the consumer units - they appear to be in good condition. It is not necessary to upgrade every time that a new edition or amendment to BS 7671 is published. What should be done, however, is to ensure that the new work complies with the current edition and right now AMd 1 and Amd 2 are both current.

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