Upgrade sub-main CU (for registration)

[MK-MIKE]

Hi all,

Be kind it's my first post.

I've been asked by a friend of the family to do some work on the electrics, which is good as I hoping to get my Part P assessment done this year.

The house had a LOT of work done to it about 10 years ago, including a substantial extension and a garage built. The house actually has 3 consumer units!. A sub-main to the new extension of the house and another in the garage. Now the fun starts.

The is bugger all documentation, even the CU's aren't labelled! and just for fits and giggles the garage is supplied from a 50A MCB on the un-protected side of the main CU with 10mm T&E in the loft space connecting to (wait for it) 2.5mm SWA!! out to the garage which has a 5-way CU feeding lights and sockets (no RCD protection). I'm thinking i'll downgrade the MCB to 20A (probably an RCBO)

My actual concern is the 2nd CU which feeds the extension in the house. The owners are complaining of constant tripping, however if a bulb blows in the dining room/kitchen it trips the entire house. This is due to the sub-main being wired into the only RCD on the main CU.

The house sub-main is fed via 16mm T&E and connected to a 32A MCB (I'm starting to wonder who wired this up now) on the main CU which is on the RCD protected side (the only RCD).

What I would like to do is add a 100mA delayed RCD on the main CU feeding the sub-main and replace the CU in the Utility room (that CU is damaged), but I can't as the cable is T&E and I would need to protect it with a 30mA, but i'm worried about discrimination between the new RCD in the 2nd CU. I've had a brief look at the cable run and it would be a royal pain in the rear to replace the T&E with SWA.

Any ideas from the wise one's out there as I am a bit lost for idea's

Thanks

Mike

 

[telectrix]

this 16mm T/E, is it buried in walls <50mm deep? if not, no need to rcd protect it. so fitting a 100mA would be good practice.

 

[MK-MIKE]

Hi there,

Sorry forgot that bit, the T&E is run through the ceiling/loft area (the house is a bungalow with a partial 1st floor extension). however during the building works the builders have been kind enough to seal up access to what would have been the loft to half the house and most the cable run goes under what is now the first floor, hence it being a pain if upgrading to SWA

 

[telectrix]

yes but is it buried in plaster, where it can be nailed or screwed into. if not then no need for a 30mA RCD at the front end.

 

[MK-MIKE]

Ah I see, sorry , no the CU at both ends is mounted right up against the ceiling (I think Doc M didn't exist then ) so not plastered in anywhere just run through the ceiling joists.

 

[telectrix]

so there's no requirement to RCD the 16mm at it's supply end. problem sol-ved. ssssssimppppleees

 

[MK-MIKE]

telectrix you are a HERO!!!!!!

Thank you for your assistance

 

[thekingiam]

i like the phrase sssssimppppleees is that refering to that meercat advert?

 

[telectrix]

eggggggggggggssssssssssssssssackly

 

[telectrix]

telectrix you are a HERO!!!!!!

Thank you for your assistance

all donation cheques made out to CASH. LOL. just hit the thanks button mate.oh, just seen it, ta, mate.