socket wiring ring

[ljstrawson]

Ok I got you. That makes perfect sense. The kitcen and hall are on there own ring. Thanks for your help.

 

[ljstrawson]

just out of curiousty what would changing it to 20 amp from a 32 amp actually do in terms of making it safe?

 

[ajrobb]

Speaking as a novice, the way you have drawn the circuit, it is a radial circuit with branches. The CB should be less than the lowest current carrying capacity of any of the cables. 2.5sqmm T+E cable is rated variously at 20A, 21A or 27A for typical installations. As long as it isn't de-rated by running through insulation, a 20A CB is typical for a radial circuit in 2.5sqmm. You can then have as many sockets and branches as you like as long as the floor area served is less than 50sqm.

32A is the largest capacity CB to serve 13A sockets. It is typical for a 2.5sqmm ring final circuit. These circuits can only have spurs serving single sockets or FCUs (although a single socket can be 'double gang' with two outlets).

Many of the electricians in this forum dislike ring final circuits and see them as a misguided post-war cludge. Originally, ring final circuits were rated at 100% more capacity than a radial circuit using semi-enclosed fuses. This has been reduced to only 60% more with circuit breakers but there is still a chance of overloading a conductor if the circuit is poorly designed. Except for kitchens, you can get more capacity by breaking a 32A ring final circuit into two 20A radial circuits on separate circuit breakers. This also removes the chance of overloading cables and allows you to have branches serving many sockets.

Remember, building regulations specify the worst practice you can get away with without risking prosecution. In contrast, 'best practice' changes much more slowly, generally only with new inventions.

 

[ljstrawson]

thats really helpful thanks so ill think ill change it to a
20amp rather than hacking up the wall to create a ring.

 

[ajrobb]

Although it's not necessary, if you have space in the CU, an electrician could split the existing circuit into 2 radial circuits, each 20A. I think this work would be notifiable to local building control under Part P of building regulations. Electricians can certify their own work, only building inspectors can pass other people's. So, it would probably be cheaper to get an electrician to do it than to pay the fees to the council. Stir in a periodic inspection report (PIR), and you can sleep soundly. One problem is that any work is likely to snowball into bringing the circuit protection up to current regulations and might result in replacing the CU. Apart from the expense, this is actually a good thing. If you haven't already got RCD protection, it is well worth considering.

As to changing a circuit breaker, even that might come under Part P.