Mythbusting: High Voltage Systems

Mythbusting: High Voltage Systems

Barry Satur, ECA High Voltage Advisor, offers some key safety tips for professionals that work on high voltage systems.

Working with any high voltage system is dangerous. With the right equipment, experience and training, competent persons understand the risks associated with high voltage areas, maintain an awareness at all times and know exactly what they’re dealing with.

Although it isn’t the level of voltage that causes damage to people, but rather the flow of current through the body, the risk of harm occurring within a high voltage application increases significantly due to the nature of the equipment within the area and the skills needed to safely interact with it.

Any person entering an HV enclosure should have received a level of training necessary to competently and safely enter and work within this environment. Competency is determined at different levels of experience, training and authorisation. An authorised person may be in charge of a team of individuals with a similar skill set or may have an authorisation to allow them to undertake tasks such as high voltage switching, testing and commissioning.

The term ‘high voltage’, unsurprisingly, denotes electrical energy at voltages high enough to inflict serious harm on animals and/or plants. However, over the years, voltages have been classified in different ways with very few people knowing precisely where one voltage range stops and another begins. BS7671 doesn’t quite help to understand the bigger picture. It currently defines ‘Extra Low Voltage’ as voltage not exceeding 50V AC or 120V ripple-free DC. ‘Low Voltage’ is defined as voltage up to 1,000V and ‘High Voltage as “normally exceeding low voltage”.

What’s more, there is a whole wide world outside of BS7671… the IEC 60038:2011 CENELEC Standard Voltages document provides a series of tables in which a number of different voltage ranges are grouped, and which many engineers refer to.

Clearly then, when the term High Voltage is mentioned, the first thing to do is find out what voltage (or voltages) are being referred to. It would be fair to say that, in the field of engineering services installation, voltages above 11kV are seldom encountered. However, in the electrical supply industry (outside the scope of BS 7671), voltages anywhere in the range of 230V right through to 275kV may be expected.

What are the hazards?

When working with HV, most accidents occur because people are working on or near equipment that is:

  1. a) thought to be dead, but is actually live,
  2. b) known to be live, but those involved do not have adequate training or appropriate equipment to prevent injury, or they have not taken adequate precautions.

Safety rules, safe systems of work and safe procedures all contribute to the safety of individuals by eliminating or reducing the risk. In their simplest form, these rules can be broken down into the following key points:

* Always switch off

* Secure the isolation

* Always work ‘dead’

* Never work on live equipment

Where there are extensive or complex electrical systems, especially high voltage systems, this should be reflected in clear and effective safety rules, which should embody a methodical approach so that the safety principles involved can be clearly understood and followed by everyone.

Guidance from the Health and Safety Executive covers the key elements to consider when devising safe working practices on or near high voltage electrical equipment, in their HSG85 guidance document. The relevant condensed extracts highlighted above are essential reading for managers and supervisors who control or influence the design, specification, installation, maintenance or operation of HV electrical equipment.

Competence saves lives

Throughout all the HSE publications, the word ‘competence’ re-occurs. Individuals must be suitably trained and competent to safely undertake the task they are appointed to do.

ECA proactively works with the wider industry to establish professional, safety and other operational standards with relevant stakeholders and standard-setting organisations. More broadly, ECA also looks to create commercial opportunities for electrotechnical professionals, and to represent the interests of its members who operate in the main areas of High Voltage installation.


Managers should establish a system of rules and procedures wherever electrical work is to be carried out, or ensure that contractors brought in to do electrical work have appropriate rules and procedures. These should be written down and everybody involved must be made aware of them, as they will form the basis of task-specific risk assessments.

Safety rules should set out the principles and general practices clearly and in a compact format. Those carrying out the work should be instructed to carry the safety rules with them. These safety rules should be devised to reflect, among other things, the relevant organisation, personnel, the electrical system to be worked on, and the working environment.

For more information you should visit: Further guidance can be obtained in three British Standards – BS 6423.9, BS 662610 and BS 6867.11


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