Electrical Ring Main Circuit Testing

by

Phyllis C. Miles

The UK is probably the only country in the world still using the ring main or loop system for wiring and connecting socket outlets.

Using the correct procedures for testing ring main circuits can be very useful when fault finding or verifying connections whilst carrying out electrical inspections. Here is an overview of some ring main testing techniques:

Please note: The following procedures are for dead testing only, so the distribution board and the circuit must be isolated from the electrical supply. The circuit you are testing must not be \’live\’!

Ring Continuity Test

Set your test meter to low resistance setting and zero the test leads.

Test ring continuity resistance of each of the live, neutral and earth conductor ring loops. Record these end to end readings for future reference and entering onto a test sheet.

Note: Where the earth conductors are smaller, the resistance will obviously be higher. 1.5mm will be 1.66 times higher than 2.5mm .

Super Loop Test L&N

Cross connect the live and neutral conductors from opposite ends of the ring and to form a super loop. If at first this sounds confusing, try drawing the live and neutral loops of a ring circuit on a piece of paper with the opposite ends connected. You ll see that it forms one big loop. This gives you a good basis for easily checking all the socket connections for high resistance without removing their covers.

Then test between the ends you have just connected together. The resistance reading taken between the superloop ends should be about half that of your previous continuity reading. You can then verify the ring main wiring and connections by going to each socket outlet and testing between live and neutral. Where the socket is on the ring and the connections are good , your readings should be within 0.05 of your original superloop reading at the distribution board.

These readings are not normally recorded but will form the basis for your assessment of the ring main circuit connections.

High resistance readings could indicate that the socket is on a spur from the ring, that connections need tightening or that the socket is faulty giving a poor connection to the plug and needs replacing. Where the readings are not consistent this could indicate that there are cross connections and the ring circuit has been bridged.

Super Loop Test L&E

Cross connect the line and earth conductors from opposite ends of the ring and to form a super loop.

Measure resistance between the ends you have just connected together. The reading taken between the superloop ends should be about half that of your previous continuity reading. You can then verify the ring main wiring and connections by going to each socket outlet and testing between live and earth. Where the socket is on the ring and the connections are good , your readings should be within 0.05 of your original superloop reading at the distribution board. Testing between live and earth in this way also checks for correct polarity.

High readings could indicate that the socket is on a spur from the ring, or that connections need tightening or that the socket is faulty giving a poor connection to the plug and needs replacing. Where the readings are not consistent this could indicate that there are cross connections and the ring circuit has been bridged.

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ring main testing

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