Electrical Test and Electric Motors

As well as the level of voltage, charge or current and the nature of the environment, there are a number of other factors that need to be considered when you are assessing the risk of injury arising from electrical testing work. A risk assessment should be carried out before testing begins, to help you identify the precautions you need to take. Some questions to ask when carrying out the risk assessment are:

(a) Can the work be done with the equipment dead or energised at a safe voltage or current?
(b) Is it absolutely necessary for someone to be working on or near to equipment that is live at dangerous voltages or current levels?
(c) What is the maximum voltage on conductors that will be exposed during the work activity?
(d) Are the testers competent? Are they adequately trained and knowledgeable to do the particular work and ensure that others are not put at risk?
(e) If testers are not considered fully competent, are they adequately supervised?
(f) What physical safeguards should be applied to the equipment under test to prevent injury, eg the use of temporary or permanent screens?
(g) Is the test instrumentation of safe design? Has it been properly maintained?
(h) Is it necessary to set up a permanent test area separate from the rest of the workplace, where equipment can be taken for testing? Is it necessary to set up a temporary test area around the equipment?
(i) Are the testers able to supervise the working area sufficiently and at all times to prevent danger to others?
(j) Where testing is part of an ‘after sales service’ how much must be done at customers’ premises? If testing is being done in a customer’s home, what special precautions are required to protect the tester and others?
(k) To what extent should the testers be supervised or accompanied?
(l) If the testers design, manufacture or use any special test equipment, does it meet the safety requirement of statutory body eg. BS EN 61010-1?
(m) How big is the unit under test and how much space is required around it to undertake the testing in a safe and unconfined manner?
(n) Are all the other workshop employees competent to avoid danger if there is a need for them to approach the equipment? If not, how can you make sure that they do not do so?
(o) Will the equipment be left unattended while live, for example while being ‘soak tested’?
(p) Does the workbench or separate area require a warning, eg a light, to show that testing is in progress?
(q) Is there a need for additional emergency switching devices for use by other employees to reduce the degree of injury to testers? Can residual current devices (RCDs) be used to provide supplementary protection?
(r) Is it possible to reduce the number of available paths to earth to reduce the likelihood of a phase-to-earth shock, eg by the use of barriers, screens and insulating mats?
(s) Is it possible to use unreferenced supplies, eg isolating transformers/batteries to reduce the likelihood of a phase-to-earth shock?

Injury can occur when live electrical parts are exposed and can be touched, or when metalwork which is meant to be earthed becomes live at a dangerous voltage. The likelihood of touching live parts is increased during electrical testing and fault-finding, when conductors at dangerous voltages are often exposed. This risk can be minimised if testing is done while the equipment is isolated from any dangerous source of supply, although this cannot always be done, and care must also be taken to prevent contact with any
hazardous internally produced voltages.

The most dangerous injuries are those caused by electric shock. This is because the effects of a shock are largely unpredictable and can easily lead to a fatal injury. However, there is also a risk of burn injuries resulting from arcing when conductors are accidentally short-circuited. A secondary risk can be the harm caused by a person reacting to an electrical injury, for example by falling or being traumatised by the experience.

Electric shocks occur when contact with a live conductor causes sufficient current to pass through the body to cause an injury. As a rough guide, voltages exceeding 50 V ac or 120 V ripple free dc should be considered hazardous in a dry, unconfined, non-conductive location. These voltage values must be reduced if the location is wet, confined or conductive, so where there is an adverse environment, those in charge of the work and those doing the work should be aware of the probable increase in injury risk.

In some equipment, for example microwave ovens, high voltages of several thousand volts are used and there is a very high risk of fatal injury if the exposed conductors are touched at these voltages. Injury may also be caused by currents as low as 5 mA or by stored charges.

Suitable precautions must be taken to prevent contact with stored charges in excess of 350 mJ. If the skin is pricked or cut at the point of contact, the shock current (and hence the seriousness of the injury) will be higher. Healthy skin may also become damaged at the time of contact either by the burning effect of the current or by penetration from sharp-ended conductors.