I just thought of something

mapj1:
So, if I understand you correctly the two ring cables going to a socket are "bridged out". I can not visualize this situation please explain further.


Well, imagine a ring feeding a thin corridor - leg A feeds one side, lets call those  sockets 1, 3,, 5 and leg B feeds the other side, lets call those  sockets 2,4,6.  5 and 6 link at the far end.

All is  well with the world. now imagine that the room is redecorated or in some way renovated and 'plink' some cables get drilled, cut or sockets are moved for wallpaper and the free ends now drop below the floor, pairs from socket 4 and 3 perhaps.

In the faff of fishing to reconnect , as a first go, cables are linked incorrectly and now we have two a short rings, one with no supply.  But the reason may not be realised.

123 work but 456 are dead, maybe it does not seem to reach and a junction box is added.

To fix this some re-linking is done, and now we have a ring with a cross-bar in the middle, so all sockets work  most still have 2 wires , but a couple of sockets now have 3 wires, or there is a JB under the floor.

It will pass a 'ring round' test from each socket, so you may think you have ring. This is where the fig8 test comes in,


Oddly as I type this I know I have some artefact that  must be something a bit like this in my own house, but not exactly where, and I have simply convinced myself it can wait until the bedroom floor comes up - there is a bed side socket with a sort of bypass via the bedside socket in the other room, in that you can take either one socket off, and the ring remains continuous, take both off, and it does not. Somewhere there is a JB or 2 I have not yet found. I've only lived here 16 and a bit years,...


Now  a fig 8 is not in the onsite guide,  but like the lolliop or the ring with a fat spur with more than one socket, it may be fine - it is in a sense a lollipop with the feeder radial replaced by another pair,  but to work out if the cable lengths and socket locations means it is OK or not is probably harder work than fitting a 25 A MCB or rewiring it as a proper ring.


The really bad one is the 'crab claws' or 2 radials where it probably is best to step down to 20A and call it a center fed radial.

Mike.

The chances of the corridor ring scenario is most unlikely to happen in real life. Almost impossible I would say. And if it did, which I doubt very much, we would have a ring comprising sockets 1, 3, 4 and 2. Also a ring of 3, 5, 6 and 4.


Electrically this is not unsafe regarding current carrying capacity of conductors or earthing. Also if the 5 and 6 link was left out no problem would exist, they would just become two unfused spurs.


An experienced electrician would notice that something was wrong and would not link sockets 3 and 4. Even a D.I.Yer having read his Readers Digest book of Home Electrics would not make this silly mistake.


Z.




 

mapj1:
So, if I understand you correctly the two ring cables going to a socket are "bridged out". I can not visualize this situation please explain further.


Well, imagine a ring feeding a thin corridor - leg A feeds one side, lets call those  sockets 1, 3,, 5 and leg B feeds the other side, lets call those  sockets 2,4,6.  5 and 6 link at the far end.

All is  well with the world. now imagine that the room is redecorated or in some way renovated and 'plink' some cables get drilled, cut or sockets are moved for wallpaper and the free ends now drop below the floor, pairs from socket 4 and 3 perhaps.

In the faff of fishing to reconnect , as a first go, cables are linked incorrectly and now we have two a short rings, one with no supply.  But the reason may not be realised.

123 work but 456 are dead, maybe it does not seem to reach and a junction box is added.

To fix this some re-linking is done, and now we have a ring with a cross-bar in the middle, so all sockets work  most still have 2 wires , but a couple of sockets now have 3 wires, or there is a JB under the floor.

It will pass a 'ring round' test from each socket, so you may think you have ring. This is where the fig8 test comes in,


Oddly as I type this I know I have some artefact that  must be something a bit like this in my own house, but not exactly where, and I have simply convinced myself it can wait until the bedroom floor comes up - there is a bed side socket with a sort of bypass via the bedside socket in the other room, in that you can take either one socket off, and the ring remains continuous, take both off, and it does not. Somewhere there is a JB or 2 I have not yet found. I've only lived here 16 and a bit years,...


Now  a fig 8 is not in the onsite guide,  but like the lolliop or the ring with a fat spur with more than one socket, it may be fine - it is in a sense a lollipop with the feeder radial replaced by another pair,  but to work out if the cable lengths and socket locations means it is OK or not is probably harder work than fitting a 25 A MCB or rewiring it as a proper ring.


The really bad one is the 'crab claws' or 2 radials where it probably is best to step down to 20A and call it a center fed radial.

Mike.

The chances of the corridor ring scenario is most unlikely to happen in real life. Almost impossible I would say. And if it did, which I doubt very much, we would have a ring comprising sockets 1, 3, 4 and 2. Also a ring of 3, 5, 6 and 4.


Electrically this is not unsafe regarding current carrying capacity of conductors or earthing. Also if the 5 and 6 link was left out no problem would exist, they would just become two unfused spurs.


An experienced electrician would notice that something was wrong and would not link sockets 3 and 4. Even a D.I.Yer having read his Readers Digest book of Home Electrics would not make this silly mistake.


Z.