The UK was the first and probably the only country in the world that still uses the 30 amp ring system for wiring sockets. The large ring circuit has been the subject of much discussion among electricians, but as an electrician you will undoubtedly need to test them in your work. Here is a summary of Ring Main inspection and testing procedures.
Caution- Please note that this is a ‘dead’ test so the distribution board, consumer panel or circuit must be electrically isolated. First you need to do the Safe Isolation Procedure and get permission to turn off the property.
Here’s how to try it:
Insulation resistance
Connect all devices and equipment from the ring circuit and test the measurements between Line, Neutral and Earth CPC.
End to End Ring Continuity Testing
Set your test meter to low resistance and ‘zero’ test leads. Measure the resistance of the ring continuity of any type of living, political and terrestrial rings. Write this end to end for future reference and enter the test paper. Note that where the earth conductors are small, the resistance will obviously be high. For example, twin and earth cables 1.5mm will be 1.66 times longer than 2.5mm.
Super Loop L&N test
Connect the live and neutral conductors from the ends of the ring and form a top loop. If at first this sounds confusing, try to draw the live and neutral loops of the ring circuit on a piece of paper with some connected parts. You will see that it forms one very large loop.
Measure the resistance between the ends you just connected together. The reading taken between the ends of the upper loop should be about half of what you read continuously. You can verify mains wiring and connections by going to each socket and testing between live and neutral. Where the socket is on a ring and the connections are ‘good’, your readings should be within 0.05 of your initial loop reading on the distribution board.
This reading is not recorded but will be the basis for reading the ring main circuit.
A high reading may indicate that the socket is on a spur from the ring, that the connections need tightening or that the socket is faulty by giving a bad plug connection and needs to be replaced. Where the readings do not match, this may indicate that there are contacts and the ring circuit is connected.
Super Loop Test L&E
Connect the line and the earth conductors from the ends of the ring and make a super loop. Measure between the two sets of ends you just joined together. Critical reading should be about half of what you read continuously. You can verify the main wires and connections by testing the resistance on each socket as Live and Neutral we explained earlier. Testing between life and earth on metals also checks for correct polarity.