CAN WE AFFORD TO CUT CORNERS WHEN IT COMES TO SAFETY?
The consequences of not properly checking that a circuit is dead can not only be fatal, but can also have serious financial penalties for employers. Neil Hayden from the ECA and Steve Dunning, managing director of Martindale Electric, talk us through the checking process, the range of voltage indicators available and the importance of proving devices
What are the dangers in not properly testing that a circuit is dead?
Around 1,000 electrical accidents at work are reported to the Health and Safety Executive (HSE) each year, and about 30 of these are fatal. However, even non-fatal shocks can cause severe and permanent injury. Shocks from faulty equipment may lead to falls from ladders, scaffolds or other work platforms. So the message is clear – electricity can, and does, kill!
What should the checking process involve? Most accidents can be avoided by taking simple precautions when working with or near electricity, which will significantly reduce the risk of electrical injury to you and others around you. The most important one must be to work on circuits and equipment that are proven to be dead ‘at the point of work’. A typical example scenario might be a situation where cables are safely isolated and locked off on one side of a wall, then emerge from the other side and are terminated in a joint box. It must be the same cable, mustn’t it? We have seen this scenario many times and, of course, it’s the same cable type – but not the same cable. So it’s always important to prove it’s dead ‘at the point of work’ – that is, where you are going to touch it.
Of course, live electrical circuits look the same as dead ones, but the consequences of working on a live circuit as opposed to a dead circuit can be tragically different. Irrespective of the pressures contractors are now commonly put under to carry out live work in areas – such as construction sites, data centres, high-cost manufacturing plants and in retail outlets operating around the clock – where power shut downs would result in serious financial losses, health and safety regulations still apply. Live working should only be carried out in accordance with the Electrical Safety Council’s (ESC) guide, derived from HSE guidance. The ESC guide states that:
No person should be engaged in any work activity on, 26 ECA Today May 2012
or so near, any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise, unless – a. It is unreasonable in all circumstances for it to be dead; and
b. It is reasonable in all the circumstances for him to be at work, or near it, while it is live; and
c. Suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury.
The guide stresses that all three conditions must be met in order for work on or near live conductors to be carried out. So the message is crystal clear: where possible, only work on dead circuits.
What steps should you take? The most obvious step to take is to lock off a circuit and ensure no live source exists by means of a voltage indicator; that’s after an initial test to make sure that the tester is working. It’s a good discipline to check your tester before and after you’ve proved the circuit to be dead – just in case your tester has just failed.
What types of voltage testers are available? The voltage tester itself should be rated to CAT III for building wiring or CAT IV for use between the distribution board and the substation. A tester capable of handling an overvoltage level of 300V (CAT III) would be adequate for most installations but, as many commercial premises have three-phase supplies, a 600V (CAT III) instrument capable of reading up to 600V would be a more flexible option.
What should you be looking for when selecting a tester? Firstly, make sure that the tester fully meets the BS EN 61243-3 standard, is of a suitable overvoltage category and rating to suit the installation being tested, and identifies both AC and DC voltage.
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