ELECTRICAL SERVICES Working safely around electricity
Steve Dunning, managing Director of Martindale Electric, explores why building services engineers must ensure safe isolation processes are part of every project involving electricity
O
fficial statistics tell us that between 2017/18 and 2021/22, 51 people died in electrical accidents in the workplace in Great Britain. Research carried out by
the Health and Safety Executive in 2010 showed over 56,000 reported accidents were electricity related, while 6% of the total number of fatal injury accidents over the previous seven years had resulted from contact with electricity. 10% of all fatal injuries were electricity related. Statistics such as these demonstrate the importance of electrical safety and how we can never be complacent. It is for this reason that safe isolation is so important, and that companies and contractors have proper procedures in place to ensure this is done right. So important is this task, that it is recognized in law. Clauses in both The Electricity at Work Regulations (EAWR) 1989 and The Management of Health and Safety Regulations at Work Regulations 1999 require those managing electrical work to take steps to ensure a safe working environment. Safe isolation and proving dead is not always simple. For example, it can be difficult to tell whether an unexpected voltage reading after a circuit has been isolated is actually hazardous or simply a phantom voltage caused by capacitive or inductive coupling from a live wire running in close proximity. If the voltage is back-fed, the result of an unwanted inter connection between circuits, it will be hazardous. In the Electrical Safety First Best Practice Guide for Safe Isolation Procedures, circumstances are identified where the neutral conductor can become live when disconnected as a result of ‘borrowing’ neutrals in lighting and control circuits. This is not permitted by BS7671 because its dangers are apparent, but the practice is not uncommon. To establish real confidence around safe isolation and proving dead requires a rigorous approach. Each stage - isolation, locking off, proving dead and labelling - should be carried out in a systematic and methodical manner. Guidance from Electrical Safety First, the UK charity which works across the electrical industry and government to reduce deaths and injuries caused by electrical accidents, states that contractors should use a dedicated voltage
indicator (VI) and proving unit to prove dead before any work is carried out on a circuit. With all this in mind, Martindale has created a new, simplified version of its 12-step process in the hope its memorable acronym - “ALIVE” - can prevent injuries and save lives. The new process highlights five vital steps which must be carried out to prevent injury and loss of life. Streamlining the message allows those who work with electricity to focus on the most vital elements.
ALIVE: 5 fail-proof steps to safe isolation
A - Approved Kit Your equipment should meet all legal safety standards (BS EN 61243-3) and you should check this before you begin work.
L - Lock Out
Identify the point of isolation and lock it off. Remember to place warning tags on the equipment.
I - Initial Prove Test your Voltage Indicator against the proving unit to make sure it’s working properly.
V - Voltage Test Use your Voltage Indicator to confirm there are no dangerous voltages in the circuit you are about to work on.
E - Ensure Finally, prove and re-test the Voltage Indicator against the proving unit to ensure it’s still working. When this is done, you are ready to start working on the circuit with confidence.
Equipment
It’s important to choose the right equipment and a proving unit and lock off kits should always be available. The point of isolation should be identified, it should be locked off and warning tags placed on all the equipment. A lock off kit should include, at a minimum, a selection of MCB and breaker locks, a padlock with a unique key, a hasp if more than one person is working on a system, lock-out tags and warning labels.
If equipment can be turned off but not isolated, then the person performing the work should isolate at the point of connection, and then trace the supply back to a point where it can be locked off. This is because if equipment is proven dead, only for someone else to restore power, the hazard has returned. An important point to remember when working on existing sites is that labelling can be misleading. Alterations could have been made by unqualified or untrained staff. And even where changes are safe, the labelling might be incorrect. Choosing the correct voltage indicator (VI) is another point to consider. The best VI models take no batteries, and have no ranges or switches, which makes them very user-friendly. 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 a 1000V CAT IV 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.
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 meters 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. 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. 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.
22 BUILDING SERVICES & ENVIRONMENTAL ENGINEER NOVEMBER 2022 Read the latest at:
www.bsee.co.uk
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