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Safety verification test of mains polarity with supply live

Safety verification test of mains polarity with supply live

Below is a how-to guide on mains polarity, safety verification testing, with supply live. This is additional to, and does not substitute for verification guidelines contained in standard AS/NZS 3017.

This guide is indicative and prepared on the basis that the electrical practitioner will:

  • never enliven mains to carry out this safety verification test, unless correct polarity has first been established.
  • be appropriately trained, qualified, authorised and competent to carry out the tests;
  • use a suitable meter and safety equipment, follow all necessary safety procedures; and
  • have a suitable purpose-built polarity tester, complete with trailing test lead and earth probe.

Testing safety notes

  • Correct mains polarity should always be confirmed first before carrying out this live test and failure to do so can create an immediate and serious risk of electrocution, shock, or fire.
  • Always ensure meter is functioning correctly using the Prove Test Prove method.
  • While testing ensure that the earth probe and all connections are not touched as they can or will become live during testing or fault conditions.
  • Ensure all connections are secure and reliable to help achieve true and accurate results.
  • Repeat tests a number of times (if required) to ensure accuracy and consistency of test results.
  • If the supply neutral is not connected and earthed then the installation is not safe to use.

Tip icon Notes for step 1

Note 1.1 First test to the outside of earthed metal meter box or earth electrode and other parts of the earthing system including bonded metal parts/pipes.

Note 1.2 With a digital voltmeter the value should be a very small a.c. voltage, 0.2 to 2V would normally be indicated.

If the result is different -

transposition has occurred, take appropriate safety procedures.

Tip icon Notes for step 2

Note 2.1 Using a volt meter, test from independent earth probe to main neutral conductor.

In this example, the neutral test point is available from the neutral joint lug inside the meter box.

However some installations will require the main neutral to be accessed in a different place.

Note 2.2 With a digital voltmeter the value should be a very small a.c. voltage, 0.2 to 2V would normally
be indicated.

If the result is different -

transposition has occurred, take appropriate safety procedures.

Tip icon Notes for step 3

Note 3.1 Using a volt meter, test from independent earth probe to incoming phase/ phases of the installation.

This point can typically be the supply main switch at the meter box or at some other suitable access point.

Note 3.2 Approximately 230 Volts a.c. should be indicated. The values obtained depend on the effectiveness of the independent earth and the type of test instrument.

If the result is different –

check for possible faults or disconnections in consumer’s mains. The electricity supply may not have been connected or livened.