Hazards of Neutral Conductors
Safety Alert: Hazards of Neutral Conductors
Safety Alert No: 33
This alert has been issued following a recent serious incident in NSW, where an electrician sustained an electric shock after cutting into an isolated power cable that became energised via a neutral back-feed on the electrical installation.
Although the power circuit being worked on had been correctly identified and isolated at the distribution board, a number of factors contributed to this incident, including:
• Inadequate testing of the power circuit, by relying solely on the use of a voltage proximity tester, commonly known as a ‘volt stick’;
• Failure to undertake a positive test and verify the absence of voltage on the conductors, by using an alternative test instrument such as a multimeter; and
• The rise in potential to 230 V of the neutral conductor, once it had been cut by the electrician - this electrical safety hazard arose because of an intermixed circuit on the electrical installation.
The safety alert reminds employers and those in control of workplaces that occupational health and safety legislation requires them to ensure that electrical work and electrical testing on an electrical installation is carried out using a safe system of work.
It suggests electrical workers should conduct a site-specific risk assessment and identify the risks associated with the work (including voltages on disconnected neutrals), and use the following control measures:
• Identify the circuits and apparatus to be worked on, and the appropriate sources of power supply; • De-energise the circuits and apparatus, and isolate from all sources of supply;
• Ensure the supply remains isolated, by locking off and/or tagging the isolator;
• ‘Test before you touch’ - prove and verify the supply is de-energised by using appropriate test methods and approved test instruments, to test for the absence of voltage on all conductors, including the neutral conductor (‘volt sticks’ should only be used as an indicator and should not be relied on to verify if a circuit is energised or de-energised);
• Use appropriate clothing and personal protective equipment; and
• When leaving unfinished work, ensure that it doesn’t present a hazard to others at the workplace. Electrical tradespeople should note that when proximity voltage testers are used to prove de-energisation, they must be tested for correct operations immediately before use and again immediately after use - particularly if the test result indicates zero voltage - to confirm that the instrument is still working correctly.