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To test or not to test - that is the question

The reality is that everyone makes mistakes, even the very best of us. Plus, when making a repair or addition, you don’t know how well the original work was done. Testing helps electricians to identify hazards and reduce the risk of serious problems down the track. It’s better to spend half an hour on prevention than thousands of dollars and many hours of work, defending yourself in court. As Benjamin Franklin once said “An ounce of prevention is worth a pound of cure.”

Testing, as required by the electrical safety [installation] regulation, was a hot topic during our roadshows across Melbourne. The subject was well received, sparking much discussion among attendees. We discovered that an overwhelming number of electricians thought that testing electrical work only applies to new installations. In fact, the law states that electrical testing is mandatory for all types of electrical work – new installations, addition and repairs.

Australia’s electrical testing requirements and minimum acceptable test results can be found in section 8 of AS/NZ3000 – Wiring Rules, as well as in AS/NZ 3017 – Guidelines for testing of electrical installations.

There are six mandatory tests;

  • Continuity of earthing systems
  • Insulation resistance test
  • Polarity testing
  • Correct circuit connections
  • Verification of impedance required for automatic disconnection, earth fault loop impedance
  • Operation RCDS

The type of work being completed determines which of these tests are required. For example, RCD testing obviously wouldn’t be required after the replacement of an electrical equipment which isn’t protected by a RCD. Let’s examine each of these test requirements to see what’s involved why it’s important.

  1. Continuity of earthing systems

An adequate earthing system consists of:

  • MEN link
  • Main earthing conductor
  • Protective earthing conductors
  • Earth bonding conductors
  • Functional earthing conductor

Each of these elements plays a critical role in the safety of an electrical installation. The MEN link connects an installation’s main earthing and neutral conductors. It plays a Key role in enabling protection devices to operate in the event of an active to the earth fault, so its existence, location and resistance are critical. The main earthing conductor is connected to the earthing electrode which provides and alternative return path to the substation in the event of a fault. The impedance of this conductor has to be as low as possible and must never exceed 0.5ohms

Each part of an earthing system has its own specific design and testing which are all detailed in the Australian standards.

  1. Insulation Resistance (IR) Test

IR testing is used to stress the insulation of conductors by applying a voltage well above the installations nominal operating voltage to ensure that it won’t break down during normal operation.

The key to successfully testing insulation lies in the correct preparation of the installation prior to testing. Depending on the scope of your work, tests can be applied to an entire installation or parts of it. In all cases, live conductors must be disconnected before the test can be conducted.

These days most installations contain sensitive electronic devices such as light dimmers and drivers for LED lighting. Your preparation needs to take this into account, as electronic equipment within the installation can be easily damaged when applying 500V from an insulation tester.

  1. Polarity Testing

Put into a nutshell, polarity testing is a process to ensure conductors are identified correctly and are the same at the beginning and the end of the circuit. In other words, that active is active, neutral is neutral, and earth is earth all the way from the distribution board to the end point of every sub circuit.

When switching conductors, polarity testing also ensures that;

  • No earthing conductors are switched, and
  • Active conductors are switched, and
  • If neutral conductors are switched then the associated active conductor is also switched simultaneously

According to Energy Safe Victoria, Reversed polarity of an electrical installation is a major and will result in prosecution

  1. Correct circuit connections

This is all about ensuring that all end point devices are correctly connected and that active, neutral and earth conductors can be identified. This includes verifying that socket outlets are wired in the correct sequence and that hardwire equipment is installed in accordance with manufacturer’s instructions.

  1. Verification of Impedance required for automatic disconnection (Fault Loop Impedance)

As the name implies, this is a loop test which includes the active conductor and earth conductor. If supply is available, the test can be conducted using a fault loop impedance tester. Testing a final sub-circuit can be as simple as plugging the tester into a socket outlet. The tester provides the impedance value which can be checked against table 8.1 of AS/NZS3000.

Where no supply is available, a bridge is installed at either the socket outlet end or switchboard end between the active and earth conductors. An ohm meter is used to measure the value of resistance which is then compared with the values in table 8.2 Australian Standards.

  1. Operation of RCD’s

In Australia, the only requirement for testing RCD’s, outside AS/NZS 3012 is to test the trip circuitry by simply pushing the trip button and verify that it trips.

For support, guidance or further specific information, contact NECA Technical Manager, Roy Sand on 1300 300 031.

 

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