A refurbishment job in a second floor flat presents a few problems for a Voltimum user...
This Q & A is one of thousands posted in our Technical Expertise area, and answered by our Voltimum Experts.
Question:
I am working on a refurbishment job on a second floor flat.
I have done the inspection and have started on the remedial and new installation work. The problem I have is the sub-main meter tails and earth conductor pass through a flat on the first floor and are flush mounted along with their meter tails to their consumer unit.
I need to RCD protect this cable and provide RCD protection for the second floor flat circuits too.
Rerouting of the sub-main is very awkward so I need to find a suitable arrangement to protect it as it is.
Can I just use the one 30mA RCD at the sub-main fused switch and a standard MCB consumer unit in the flat? Or do I still need the two RCDs in the flat with the possibility of both a flat RCD and sub-main RCD tripping?
Thank you for your advice.
Answer:
Gary Parker - Senior Technical Support Engineer
Have a look at Regulations 522.6.201-204. These give the options for additional protection of cables.
Essentially you need to provide additional protection to cables that you install in a wall, but RCDs are just one way. You could use an armoured cable, or cover the PVC cables in something that will stop a nail/screw going into them.
Of course, this is only a requirement for cables you install, if the existing PVC cables are there, then you do not need to provide the protection, though it is worth talking to the client about this.
A single RCD can cause inconvenience in the event of a fault, especially if it is located remotely. So having a single 30 mA at the origin is not a great idea.
If you are putting new tails in, then I would look at an SWA, then use a standard CU in the flat, with either twin RCD or RCBOs.
If you are just renewing the CU, then leave the tails as they are, make a note that they are lacking in additional protection, and leave it with the client.