• • • TEST & MEASUREMENT • • •
An important point to remember when working on existing sites is that labelling can be misleading. Unqualified or untrained staff could have made alterations. And even where changes are safe, the labelling might be incorrect.
Check your indicators Choosing the correct voltage indicator (VI) is another point to consider. The best VI models use no batteries and have no ranges or switches, which makes them very user-friendly and reduces the chances of error. The unit should comply with BS EN 61243-3 and be specifically designed to meet this regulation. Another thing to look out for is whether the units have an appropriate category (CAT) and voltage safety rating following BS EN 61010, as suggested by BS EN 61243. This safety rating tells you that the unit can cope with the risks from hazardous transient impulses on the mains supply system. BS EN 61010-1 Installation Categories (CAT ratings) are based on where you are working:
Measurement Category I refers to measurements performed on circuits not directly connected to the mains supply, or specially protected secondary circuits such as those powered by regulated low-voltage sources. Measurement Category II refers to measurements performed on circuits directly connected to a low-voltage mains installation and might include standard 13A socket outlets, household appliances, portable tools and equipment.
Measurement Category III refers to measurements performed within a building’s permanent installation: distribution wiring including mains bus, feeders and branch circuits or hard-wired loads.
electricalengineeringmagazine.co.uk ELECTRICAL ENGINEERING • MAY 2025 49
Measurement Category IV refers to the supply side source of the building’s installation, for measurements performed at the source of the low-voltage installation such as electricity metres and measurements on primary overcurrent protection devices and ripple control units. It also includes devices and locations between the supply side of the building and the source, typically a substation.
Prove it Testing for dangerous voltages on any circuit conductor, whether single or three-phase, is the next step. The best way to do this is to use a dedicated proving unit matched to the VI to fully test all LEDs on all ranges are working. This is a much safer method than using the mains and provides a live source wherever you are working.
If no voltage is detected and the circuit is dead, then the VI should be re-tested using the proving unit. If it’s working correctly, then the operator has proved dead. The system is now safe to begin work on.
By incorporating a proving device into an electrical safety process, that process becomes inherently more robust and reliable. Although a relatively straightforward addition, when working with or near electrical systems and equipment, a proving device can significantly reduce the risk of electrical injury to you, your team, and others around you.
For the latest electrical safety advice and downloads visit: https://martindale-
electric.co.uk/safe-isolation-7/
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