How to test the main circuits of the electric ring
The UK was the first and is now probably the only country in the world still using the 30 amp ring system for wiring outlets in electrical installations. The main circuit of the ring has long been the subject of much heated discussion among electrical experts, but as an electrician you will no doubt need to test them in the course of your duties. Here’s an overview of Ring Main’s inspection and testing procedures.
Warning: Please note that this is a ‘dead’ test, so the distribution board, consumer unit or circuit must be isolated from the power supply. To get started, you will need to perform a Safe Isolation Procedure and get permission to turn off the power.
Here is the test procedure:
insulation resistance
Disconnect all devices and accessories from the ring circuit and perform insulation tests between the Line, Neutral and Earth CPC.
End-to-end ring continuity test
Set your test meter to the low resistance range and zero the test leads. Measure the ring continuity resistance of each of the hot, neutral, and ground ring loops. Record these end-to-end readings for future reference and enter on a test sheet. Note that where the ground leads are smaller, the resistance will obviously be higher. For example, for twin and ground wires, 1.5mm will be 1.66 times greater than 2.5mm.
L&N Super Loop Test
Cross connect the hot and neutral conductors from opposite ends of the ring and form a super loop. If this sounds confusing at first, try drawing the hot and neutral loops of a ring circuit on a piece of paper with opposite ends connected. You’ll see that it forms a big super loop.
Test the resistance between the ends you just connected. The reading taken between the ends of the super loop should be about half of the previous continuity reading. You can then check the main ring wiring and connections by going to each outlet and testing between hot and neutral. Where the socket is in the ring and the connections are ‘good’, your readings should be within 0.05 of your original super loop reading at the distribution board.
These readings are not normally recorded, but will form the basis for your evaluation of the ring’s main circuit connections.
High readings could indicate that the plug is in a leg of the ring, the connections need to be tightened, or the plug is faulty, resulting in a poor connection to the plug and needs to be replaced. When the readings are not consistent, this could indicate that there are cross connections and that the ring circuit has been bypassed.
L&E Super Loop Test
Cross connect the line and ground conductors from opposite ends of the ring and form a super loop. Try between the two sets of ends you just connected. The resistance reading should be about half of the above continuity reading. You can then check the main ring wiring and connections by measuring the resistance at each outlet as described above for Live and Neutral. Testing between power and ground at plugs also verifies correct polarity.