Two live wires at socket

[Kaymo]

Hi,
Forgive my ignorance if this is normal, but I am changing the socket front plate, and in the pic below the two red wires coming from the bottom hole are both live. This is an extension (1980's) and both cables enter the extension from under the ground just below this, and are on the same mcb as the power sockets for the downstairs part of the old house (1800's). The cable coming in the top entry is the one going to the next socket.

Is this just two cables doubled up for redundancy because of the fact that they have been run underground, or is it something to do with the circuit type. I can put it back the way I found it but I am curious.

 

[EFLImpudence]

It is (presumably) a ring circuit.
https://www.diynot.com/wiki/Electrics:socket_circuits:A1-Ring-final-Circuit

These two will go back to the same MCB in the Consumer unit.
All three will go to a next socket somewhere.

 

[Kaymo]

Thanks EFL, that makes sense, as I checked the resistance between the two and it was high, which would be the MCB in between them. I guess then the one live goes to the socket before this one in the ring, and the other to the next in the ring, and the cable coming in at the top must be a spur off from ring circuit.

 

[EFLImpudence]

Thanks EFL, that makes sense, as I checked the resistance between the two and it was high, which would be the MCB in between them.

No, they will be connected together at the same place in the MCB.
The resistance should be very low, definitely <1Ω. and the same as the neutrals. What was it?

I guess then the one live goes to the socket before this one in the ring, and the other to the next in the ring, and the cable coming in at the top must be a spur off from ring circuit.

Yes.

 

[ban-all-sheds]

I guess then the one live goes to the socket before this one in the ring, and the other to the next in the ring, and the cable coming in at the top must be a spur off from ring circuit.

Yes.

Unless one goes to the CU....

 

[ban-all-sheds]

Forgive my ignorance..

Your ignorance remains forgiveable for as long as you remain uninvolved in working on your electrics...

If you do want to fiddle with your wiring, then you do need to remedy your ignorance.

• http://www.google.co.uk/search?q=electrical+circuits+101
  
  
• http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners
  
  
• http://www.google.co.uk/search?q=uk+house+wiring+(basics+OR+101)
  
  
• http://kevinboone.net/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• https://www.diynot.com/wiki/Electrics:books
  
  
• https://www.diynot.com/wiki/Electrics:index

 

[securespark]

I would ensure all the cables' earth conductors are terminated in the socket earth terminals. If you wish, you can then run a single earth wire from there to the back box.
I consider it bad practice to terminate them in the back box earth terminal.
Plus, there's a grommet missing.

 

[Kaymo]

Terminated to the socket earth, not the back box.

I was fairly sure that there was a resistance in the Meg range when I checked this, which is why I was a bit confused. If these two cables meet at the CU then the resistance should obviously be low so I will take off and check again later.

 

[oldbutnotdead]

I'm hoping you have the main switch OFF while you're doing this rather than just dropping the MCB or pulling the fuse. The assumption of a spur off a ring final is just that- an assumption. You could be into a spur off a spur situation or a very odd radial- only way to tell for certain is to map the circuit (easy but tedious)

 

[Kaymo]

Thanks oldbutnot for the warning, I know its a spur, because I know where it goes. I also verified this with a continuity check as its termination was only a few metres away in the same room. That part I am happy with. I do intend to map the circuit when I get a chance, check why there is a resistance between the two lives and confirm where they are coming from.