Electrical – How to trace the cabling in a “Ring Main”

electricalring-main

I have a "ring main" with many sockets on it, it is clear that it has been extended over the years.

How do I trace the cabling to.

  • Check that it is a single ring
  • That only one socket is on each spars
  • That there are not any other issues.

I am hoping for a testing method that I can just apply “set by set”; assume I have access to a good quality resistance meter

Is there any software I can type all the resistance readings into that will “solve” the system and will then tell me:

  • What additional readings it needs
  • Or how all the sockets are connected.

Related but a much easier problem: Are there any “easy” ways to trace a home electrical system?

Update:

The issue I have with the standard test method and all current answers is that they assume that the sockets are connect in a single ring – I don’t know how they could detect for example two rings that have their ends joined just before the consumer unit. Or a spars that is connect to anther spars rather then directly connected to the ring.

The test in the wiring standard is very good at finding common errors like a wire that is not connected, or a live that is connected to a neutral; however the test seems to assume that the wiring is basically a valid single ring to start with. This is not a valid assumption on an old system you don’t know the history off!

Best Answer

if you can get your hands on a TDR (time domain reflectometer) you can use it to measure the distance to the end of the ring from an outlet.

  1. turn off the power to the ring and disconnect the hot from both ends at the breaker.
  2. using the TDR, measure the length of the hot circuit from where you just disconnected it at the breaker. that is the total circumference of the ring.
  3. connect the TDR to the hot of an outlet. the TDR should return two "open" or "end of wire" values. this will tell you how far this outlet is from each end of the ring.
  4. back at the consumer unit, take a short piece of wire and temporarily attach it to one of the live wires you disconnected and measured in steps 1 and 2. then remeasure the same outlet from step 3. the new measurements will tell you which "leg" of the ring goes to which wire.
  5. repeat step 3 (and step 4 if needed) for each outlet.
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