Several installations have been identified where either people at the property, or at another property, have received electric shocks due to incorrect polarity of consumer mains or submains.
Incorrect polarity connections on consumer mains or submains supplying an outbuilding with a separate multiple earth neutral (MEN), will result in an energised earthing system.
Testing will ensure any incorrect connection is identified and rectified, to prevent the risk of electric shock.
The protective earth neutral (PEN) is the most important earthing conductor in an electrical installation. The impedance of the PEN must be low enough to pass the current necessary to operate the overcurrent protective device and be consistent with the length, cross sectional area and type of conductor material.
Correct polarity testing for low voltage connections to an electricity network or where an electrical installation in an outbuilding has a separate MEN connection in accordance with AS/NZS 3000:2018, Clause 220.127.116.11(c) must:
- include a visual inspection
- ensure the use of suitably designed and correctly rated test equipment
- ensure an effective independent earth is used
- ensure that any neutral bonding conductor (i.e.to raiser bracket) is disconnected
- prove the operation of the test equipment before and after testing
- prove the identity of the incoming active conductors
- prove the identity of the incoming neutral conductor
- prove the integrity of the supply neutral and connections
- confirm phase rotation
- ensure that any bonding conductor removed for testing is tested and reconnected
- ensure that all conductors are correctly connected, including the MEN connection
- ensure a final visual and verification of correct connections is completed.
For detailed information and guidance on conducting a polarity test for supply to electrical installations and neutral integrity tests for supply to electrical installations, refer to AS 4741 (Testing of connections to low voltage electricity networks).
Remember, polarity testers which are connected to a final subcircuit do not confirm mains polarity and will indicate that polarity is correct even if there is a reverse polarity.