Sub main in a domestic property

[Zahid Nawab]

Hello all. I have visited a domestic property with two consumer units, one downstairs and then a separate one for upstairs. The upstairs is fed by a 16mm twin and earth and the downstairs is fed by 25mm tails. The cu downstairs is a duel RCD. The question I want to ask is, since the cable feeding upstairs is buried, I was planning to install the sub main directly into downstairs consumer unit. However. The problem is the issue with conflicting RCD. I don't want nuisance tripping occuring since the RCD downstairs is only rated 30ma. I was under the impression that time delay rcbo were easily available but after a bit of shopping around, it's not the case. This was my initial idea on how to resolve the issue. Thank you in advance

 

[loz2754]

A time delay RCD is not suitable for the additional protection required for cables buried in walls at < 50mm.
Possible options might be:
1. Add a small consumer unit for the sub main with it's own RCBO, by tapping into the tails before the main consumer unit.
2. I can't think of anything else.

 

[Dustydazzler]

With the 16mm T&E buried you simply cannot avoid the requirement for RCD protection at the feed end

You can change the T&E to SWA if its an easy run but apart from that you are stuck with the front loaded RCD

 

[freddo]

It's an annoying regulation. That's why I ran the concealed submain supply cable in my house in MICC.

Is the cable actually buried <50mm from the surface?