Ring mains on 20A MCBs??

[monkey5]

just a query really wondering if anyones else does this and why.

been to fit an outside light t a new property (1 year old) feed from socket in bedroom via FCU. any way come to test everything and all socket ring main are on 20A mcbs. i know theres nothing wrong with it just thought un usual on new build. all tests were find ie r1,rn,r2 (end to end).

another thing i noticed was all the ring mains (3 of) were on 1 rcd and all the lights (3 of again) are on the other, now i think this is bad design and am assuming all the other houses ( probably 100+) will be the same.

mentioned it to customer and noted on cert.

what do you guys think?

 

[wozz]

New or rewired domestic and similar installations : Electrical Safety Council

Q9. (from the horses mouth as to say)

The division of their circuits has not minimized inconvenience, but neither does mixing them up, comes from a vague regulation.

 

[cadspark]

Maybe 20 amp MCB due to cables passing through insulation and having to take account of current carrying capacity. The sockets on one RCD and lights on another is just plain bad design,

 

[monkey5]

think they were highly insulated houses so makes sense.

cheers wozz

 

[Revved Up Sparky]

Maybe 20 amp MCB due to cables passing through insulation and having to take account of current carrying capacity,

If this is indeed the case then I'm surprised the installation designers did not forsee this and run the ring main in 4.0mm instead of 2.5mm. 20A overcurrent protection will only allow loads of up to 4.6KW at 230v, that's a washine machine and a kettle !.

 

[wozz]

Id say thats where good circuit design comes in rev. Cost is a issue with 4mm and cheap sockets dont always accept two 4mm easily.

 

[monkey5]

it wasnt a massive house so 3 rings should be fine and am sure there was a seperate grid feed for washer machine and dishwasher.