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Case Studies

Wear and Tear

The outer sheath of an electrical cord is designed to be tough to protect the more delicate insulation of the inner cores. The flexibility of the sheath diminishes over time and becomes brittle, leading to cracking as can be seen here. The inner insulation is then exposed to damage, with the copper conductors becoming exposed enabling a user to come into contact...

Manufacturing Faults

At a Geelong company, we recently encountered a number of leads with a manufacturing fault. The Earth resistance of the leads was greater than the 1.0 Ohm permitted by AS/NZS 3760. An old computer lead had failed testing and the OH&S manager said they had a box full of spare leads, one of which could be used as a replacement. The spares were as a result of...

Contaminated Heater

In the winter months, some workers will bring a fan heater to work for some extra warmth. During routine electrical safety testing at a Geelong workplace, we found such a fan heater under a desk that was contaminated with a number of metal staples; several dozen in fact. It was necessary to partially dismantle the appliance to remove all the staples. When the user...

Failed Items

A competent person completed a gratis Test and Tag service for his son’s playgroup premises as the playgroup was a not-for-profit organisation and relied upon volunteers. It had been arranged that any failed appliances would be appropriately tagged as Dangerous and locked in the co-ordinator’s office until later placed out for council hard rubbish...

Safety Switches

Some competent persons have reported that an RCD (Safety Switch) will fail to trip when initially carrying out a time tripping current test but after testing with the Test push button, will pass the time tripping current test. It is thought that the push button test frees up the mechanical components of the RCD, bringing it back to specifications. Although this is...

Earth Leakage #2

The Managing Director of a company wishing to be shown the operation of Portable Appliance Tester (PAT), retrieved a power drill from a shelf for the testing. It passed the Earth Resistance test, the Insulation Resistance test but failed the Earth Leakage test. Subsequent examination found that in certain rotational positions of the chuck, it became live and thus...

Earth Leakage #1

A company that installed appliances on their client’s behalf called for technical support after two people had received a shock from one of their appliances. The appliance was subjected to an electrical safety test and passed with flying colours. Two hours later, the technician who conducted the test received a call stating that the appliance had given an...

Bond Test

A Victorian company’s appliance testing regime only found an incorrectly designed earth circuit in a large number of appliances after switching from Screen testing (100mA-200mA) to Bond testing (25A). This affected hundreds of appliances within the company. They were fortunate that none of them had become faulty before the change in practise. The manufacturer...

New Equipment

In the ’90s at a Melbourne university, a computer was being set up after purchase, only to find it wasn’t working. As the technician plugged the Ethernet cable into the rear of the computer, the Safety Switch (RCD) in the building tripped and disconnected power to the computer. It was found that the factory moulded IEC power supply cord had reverse...

Untested TV

A television mounted high on a wall was not considered as requiring inspection, testing and tagging as users did not come into contact with it. Eventually, the Television stopped working and a service technician was called. The technician set up his ladder to access the television and attempted to adjust the metal mounting bracket. He received an electric shock,...

Test Intervals

In 2006, management of an educational facility in the outskirts of Melbourne were horrified to learn that one of their buildings had been destroyed by fire, having been started by a computer monitor that had caught fire. The computer monitor had been part of a test and tag program with a 12 monthly retest interval had and caught fire only two weeks before it was due...

Electricians

There have been some cases where electricians carry out only a visual examination of appliances and many cases where some electricians who use (and thought that using) an Insulation Resistance (Megger) tester and multimeter alone would achieve all the required tests as per AS/NZS 3760 for testing and tagging. These testers cannot carry out all the required tests on...