Colleague has a house built in the late 60s and asked an interesting question. The 4 sockets in the lounge appear to be spurs rather than a ring main and I assume connected together in a box somewhere as he thinks there is one cable going to the fuse...although to be fair I suspect he is mistaken and there are 4. he had a new MCD fuse box fitted 3 years ago. Question is can he replace this spurred system like for like ? He is reluctant to have the floor downstairs and upstairs ripped up to put a ring main in and is exploring options and is hoping that the existing cables could be use to pull a new cable to each socket. Is this allowed under current regs or is he forced to have a ring main installed ?
Rewire but not putting in a ring main ?
- Thread starter topgazza
- Start date
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He does not have to have a ring final circuit installed.
he can have a radial circuit fused at 20 amps with 2.5mm cable, or 30/32 amps with 4mm cable.
Cable installed in the late 1960s is probably PVC insulated and if in good condition can be reused.
he can have a radial circuit fused at 20 amps with 2.5mm cable, or 30/32 amps with 4mm cable.
Cable installed in the late 1960s is probably PVC insulated and if in good condition can be reused.
There are very few reasons why a ring final circuit is preferable these days.
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Not yet, ring final circuits (not ring mains, they're out in the road) are still installed because that's what people do because that's what people did.
They are a legacy from rewireable fuses which need larger (or more) cable than the same rating of MCB.
The only good reason nowadays is if the circuit (sockets) actually are in a ring from close to the consumer unit and back to it.
They are a legacy from rewireable fuses which need larger (or more) cable than the same rating of MCB.
The only good reason nowadays is if the circuit (sockets) actually are in a ring from close to the consumer unit and back to it.
We very rarely install ring finals anymore, unless it's specifically spec'd. As EFLI has implied, there's very little benefit to them.
The benefits of radial finals far outweighs the benefits of ring finals IMO.
The benefits of radial finals far outweighs the benefits of ring finals IMO.
There is that, but it's also things like, with a ring final, a live cable could quite happily pop out of the back of a socket, and be floating freely around but all of your circuit will still work. In a radial, a live or neutral pops out/breaks etc then all sockets downstream of that one stop working. Makes fault finding so much easier. The same applies to the CPC, you could completely lose them in one socket but testing every other socket would say it was fine.
There is also less testing involved (makes our lives easier), but often instead of doing 2 or 3 ring finals, we might do 5 or 6 radial finals, which helps segregate things a bit more, means if one circuit trips, you've lost a lot less than ALL of your upstairs/downstairs sockets.
Did an EICR on Monday where someone had taken this to the extreme, every room (although supplied by ring finals) had sockets supplied from at least two circuits, some rooms had 3 or 4 circuits in them. Nightmare to test
There is also less testing involved (makes our lives easier), but often instead of doing 2 or 3 ring finals, we might do 5 or 6 radial finals, which helps segregate things a bit more, means if one circuit trips, you've lost a lot less than ALL of your upstairs/downstairs sockets.
Did an EICR on Monday where someone had taken this to the extreme, every room (although supplied by ring finals) had sockets supplied from at least two circuits, some rooms had 3 or 4 circuits in them. Nightmare to test
Would also like to make it clear to the OP that in such a situation your would likley have created what is now two radials circuits protected by a OCPD rated greater than the current rating of the single cable feeding each half of the sockets.
(i.e. 2.5mm² T&E cable feeding each half of the now broken ring final circuit what is protected by a 32A MCB/RCBO. Thus you end up with 2.5mm² cable that is only rated for a maximum of 27A protected by a 32A circuit.)
Technically true, but in reality, it's just a broken ring.
I often wonder when testing, what %age of ring finals out there are broken.
1/4 on Monday was open circuit on all 3 conductors
I often wonder when testing, what %age of ring finals out there are broken.
1/4 on Monday was open circuit on all 3 conductors
Before the war most houses had very few sockets, maybe one in each room at the most.
These would have been protected by a 15A rewireable fuse.
As I said these fuses require larger than 15A cable (actually 21A) so it would have been the imperial equivalent (roughly) of 2.5mm².
After the war, when more electrical appliances became available and more sockets were required, rather than replace everything, a way was devised to increase the circuit capability to 30A using the same small fuse box with only room for the one socket circuit.
A 30A radial, with the fuses, would have required a cable two sizes larger, today 6mm². This would have taken a lot of copper, which was scarce.
So they devised a way by adding sockets to the existing circuit and extending the circuit around the house back to the consumer unit making the ring. Effectively two cables in parallel of approximately 5mm².
However, restrictions were imposed (because of the danger of too much current on one side) of 66% of the current limited by the fuse so the cable must be a minimum CCC of 20A.- this after the restriction because of the fuse itself - so in actual fact 27A cable.
Therefore a circuit which would be capable of handling a load of 54A at its centre had to have a fuse of only 30A.
This is not actually the case with MCBs although the same rules still apply.
So, today:
You can have a 32A radial with an MCB and 4mm² cable or
two 25A radials (the ring split in the middle) with an MCB and 2.5mm² cable. Therefore 50A instead of 30A/32A
Actually, today you could have a 32A ring with an MCB and 1.5mm² cable but it is just specifically 'not allowed'.
These would have been protected by a 15A rewireable fuse.
As I said these fuses require larger than 15A cable (actually 21A) so it would have been the imperial equivalent (roughly) of 2.5mm².
After the war, when more electrical appliances became available and more sockets were required, rather than replace everything, a way was devised to increase the circuit capability to 30A using the same small fuse box with only room for the one socket circuit.
A 30A radial, with the fuses, would have required a cable two sizes larger, today 6mm². This would have taken a lot of copper, which was scarce.
So they devised a way by adding sockets to the existing circuit and extending the circuit around the house back to the consumer unit making the ring. Effectively two cables in parallel of approximately 5mm².
However, restrictions were imposed (because of the danger of too much current on one side) of 66% of the current limited by the fuse so the cable must be a minimum CCC of 20A.- this after the restriction because of the fuse itself - so in actual fact 27A cable.
Therefore a circuit which would be capable of handling a load of 54A at its centre had to have a fuse of only 30A.
This is not actually the case with MCBs although the same rules still apply.
So, today:
You can have a 32A radial with an MCB and 4mm² cable or
two 25A radials (the ring split in the middle) with an MCB and 2.5mm² cable. Therefore 50A instead of 30A/32A
Actually, today you could have a 32A ring with an MCB and 1.5mm² cable but it is just specifically 'not allowed'.
I was explaining the electrical principles and rules behind ring circuits to topgazza.
Is saying "you could do something but it's not allowed" suggesting he have it?
There is nothing electrically non-compliant about a 32A / 1.5mm² ring circuit apart from the fact that it is specifically forbidden.
Is saying "you could do something but it's not allowed" suggesting he have it?
There is nothing electrically non-compliant about a 32A / 1.5mm² ring circuit apart from the fact that it is specifically forbidden.
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