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11 Point test for Safe isolation on 3-phase Electrics in the UK

Sergio Fernandez

Safe isolation on 3-phase systems in the UK currently requires a 10-point test plan

A quick internet search bring up the following 10 point test plan.
L1 – L2
L2 – L3
L1 – L3
L1 – Neutral
L2 – Neutral
L3 – Neutral
L1 – Earth
L2 – Earth
L3 – Earth
Neutral – Earth

Personally I think the industry should write it down as follows

Earth to L1
Earth to L2
Earth to L3
Earth to Neutral
Neutral to L1
Neutral to L2
Neutral to L3

L1 – L2
L2 – L3
L1 – L3
It shows clearly the first 7 sets of test FROM LEAST dangerous connector/probe first


Steps to Safe Isolation

    Permission: Secure authorization to isolate the circuit.
    Identify: Locate the correct isolation point.
    Switch Off: Turn off the 3-phase supply.
    Lock Off: Secure the isolator with a padlock and keep the key.
    Warn: Place "Danger" notices and "Do not switch on" labels.
    Prove (Before): Test your voltage indicator on a known live source/proving unit.
    Test: Perform the 10-point test above.
    Prove (After): Re-test the indicator on the proving unit. 

The Lock Off: Secure the isolator with a padlock and keep the key.  Should EMPHASISE preferred lockoff is upstream from DB/CU



Important Notes:

    Always use a GS38-compliant voltage tester; voltage sticks are not suitable for proving dead


Now for the 11th test part
Use a suitable clamp meter on the tails to check for leakage current initially set to Amps then mA after the isolation step/lockoff step.  This is vital to help detect PEN faults/Diverted Neutrals




As always please be polite and respectful in this purely academic debate.





Come on everybody let’s help inspire the future

Parents
  • Sergio Fernandez said:
    Identify: Locate the correct isolation point.

    If you have done that correctly, the order of tests should not matter - the lamp does not light at all (until you prove it).

  • in reply to Chris Pearson

    My focus here was to add an 11th step to the test.  The clamp meter around the tails

  • in reply to Sergio Fernandez

    Were we not discussing safe isolation?

    If neutral is isolated, i.e. four conductors are isolated, I cannot see how there could be any current in the fifth.

    Earth leakage is from line to earth (by passing neutral), so again if the lines are isolated, there cannot be any earth leakage.

    That leaves diverted neutrals. So there could be a potential difference between neutral and earth, but if the 50 V lamp has not lit, is that a problem for safe isolation? That notwithstanding, I am not clear what comprises the circuit when all the lines have been isolated.

  • in reply to Chris Pearson
    Chris Pearson said:
    Were we not discussing safe isolation?

    No, not really. We are discussing "unsafe " isolation, or more pedantically, failed isolation and faulty installations.

    And, pedantically, it could be 6 connections and rogue fault currents once the external ground and diverted currents are included...

  • in reply to Philip Oakley

    should add that it's the checking and diagnosis of the safety of the isolation, rather than a presumption of safety through simple procedural compliance....

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  • in reply to Philip Oakley

    should add that it's the checking and diagnosis of the safety of the isolation, rather than a presumption of safety through simple procedural compliance....

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