Q & A of the Day – With this multiple occupation unit, can I remove the hall / landing lights from the RCD?

 

Question: I’ve been called to look at a problem installation in a multiple occupation unit.

 

The hall stairs and landing have three light fittings that are all connected to a distribution board having a single RCD protecting five circuits - internal landing/ stairs (including smoke detectors), porch light, external low energy floodlights, an external car parking lamp post and a cleaner’s socket.

 

The problem is that if the RCD trips, which happens quite regularly because of the cleaner, the internal lights are also disconnected. This leaves the occupiers in a totally dark hall and landing, which is a hazard.

 

There are emergency light fittings, but the situation is left with the trip activated and the battery tends to be run down on the emergency lights.

 

I am considering re-installing a distribution board with RCBOs fitted, but wanted to check whether I could remove the hall / landing lights from the RCD – can I?

 

Note that the wiring is concealed, so I am unable to confirm its depth. I suspect I know the answer…

 

Answer: Where installing a number of circuits that are protected by one RCD, the requirement of Regulation 314.2 demands consideration - i.e. circuits shall be provided in such a way that they are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.

 

The designer of the installation, in this instance, has deemed it necessary to have these circuits protected by an RCD, so I presume that it is either not that old (2008-on), or that there is another specific reason for the RCD protection having been provided. Is there, do you know?

 

You mention, however, that the existing circuit layout is not ideal and that there is a hazard, and that you intend to install a new distribution board with RCBO protection for each circuit. This would, in my opinion, be the best way of removing the hazard you describe and would meet the requirement of Regulation 314.2. However you are considering removing the RCD protection for the lighting circuits and mention that the wiring is concealed – yet you cannot confirm the depth that the cables are installed. 

 

My advice would be that unless the wiring can satisfy one of the options given in Regulation 522.6.101 - other than option (v) 'installation in safe zones' - and that it does not meet the exception allowed in Regulation 522.6.102, then the RCD protection should remain!

 

Regulation 522.6.101 in BS 7671:2008 (2011) provides a number of options where a cable is to be installed buried less than 50mm within a wall or partition. If the cables are installed in designated safe zones - option (v) - then unless the installation is intended to be under the supervision of a skilled or instructed person, additional protection by the installation of a 30mA RCD must be provided.

 

Note - BS 7671:2008 (2011) is not retrospective to installations installed to an earlier version of the standard, so the requirement for RCD protection for buried wiring might not have been applicable to this installation originally. However, as the existing design has RCD protection, I would think that a careful risk assessment would have to be undertaken to ensure that the level of safety against electric shock currently provided is not reduced.