Video- How To Test A Ring Main

by Steve on February 3, 2010

The UK is one of the few, if not the only country in the world which still uses the ring system for wiring and connecting socket outlets.  The ring main circuit has long been the subject of many a heated discussion between electricians, but  whether you are for or against, you’ll no doubt need to test and inspect them in the course of your duties.  In this training video Chris Kitcher shows how to test a ring main final circuit.  (Allow a few seconds for the video to load.)

Find more instructional videos in the Electrician’s Resources Archive.

 

Here is a rundown of how to carry out ring main final circuit testing:

Note: This is a ‘dead’ test so the distribution board and the circuit must be isolated from the electrical supply.

Safe Isolation Procedure

  • Get permission to turn off the supply.
  • Verify that the circuit you want to test is live.
  • Turn off the fusebooard and verify that the circuit is dead.
  • ‘Lock off’ the main isolation switch to the fuseboard.
  • Verify that the fuseboard is dead using test leads and a proving unit.  On a 3 phase distribution board be sure to test between all phases to neutral and earth when checking for complete isolation.

Insulation Resistance
Disconnect all appliances and accessories from the ring circuit and carry out insulation tests between the Line, Neutral and Earth.

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.

Ring Main Super Loop R1+R2 Test for Live and Earth Connections

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.

Further Investiagtion
You may need to carry out further investigations where you find irregular readings.  This can involve some considerable time and in some cases could lead to rewiring work. At this stage it’s usually a good idea to record your findings and report your observations and recommendations to the person who ordered the testing.
Note: A typical 30 amp ring circuit should be wired as a ring in the correct sized cable for the protective device. In cases where an under sized cable has been used or the ring has been broken it could be considered necessary to reduce the rating of the fuse or mcb to protect the smallest sized cable.

Earth Loop Testing
When all of the above test have been carried out you should record your results, re-connect the ring circuit conductors, replace the fuse board covers and re-energise the circuit.
When undertaking electrical inspection and testing many electricians wouldn’t feel it necessary to carry out an Earth Loop Impedance Test at every single socket on the ring main, especially after using the test procedures as described above.  This is reasonable, but Earth Loop Tests can be used to help verify your findings and test results, prove that the circuit live and check the operation of each socket and its switch.



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Find more info on R1+R2 and Resistance of Copper Conductors.

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{ 3 comments… read them below or add one }

Nathan Peters September 8, 2016 at 22:15

Good Job Mate!

Editor March 4, 2012 at 11:49

On the end to end continuity readings, where the earth conductors are smaller, the resistance will obviously be higher. 1.5mm will be 1.66 times higher than 2.5mm .

You’ll know if the cores are the right way round on your super loop by the resistance readings you get and from a little experience.

David Elgood July 25, 2011 at 21:14

Hi Steve, sound on video very low, even turning up my screen to full and your control.

Question, about the tests on the ring main, you had a system which had the same size cpc, which is great, what about 2.5 t&e as you know cpc is smaller.

Question, you mentioned getting the cores round the right way ie 1st socket live to last socket neutral, how do you find this out at the board.

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