Calculating the Arc Incident Energy

The underlying concept for safety from an electrical arc hazard is that workers can be assumed safe if the arc rating of protective clothing measured in electrical arc tests is greater than the possible arc incident energy which was established through the risk assessment.

In order for a customer to have the appropriate arc rated clothing, the end user will have carried out a risk assessment in order to ascertain the arc incident energy in the event of an electrical arc hazard.  These risk assessments are the responsibility of the end user and is specific for each electrical installation and working conditions.

When assessing the thermal risks from an electric arc event, several quantitative parameters must be measured

supply voltage arc current (eventually also bolted short circuit current) arc duration (depends on fuses, clearing time) number of conductors (arc between two or three conductors, and also towards ground), number of phases electrode gap(s) environment: “open arc” or “arc in box” distance between arc and surface of PPE worn by worker.

From the above parameters, the key risk analysis characteristic for PPE is calculated:
ARC INCIDENT ENERGY (cal/cm2 or kJ/m2 )

The calculation can be done manually, or by commercially available software.

There are various ways that end users can carry out a risk assessment to obtain this calculated incident energy rating from simplistic free of charge computer calculators to in-depth statistical studies. Care must be taken when deciding upon which method is used as each provides various incident energy levels which may affect the level of protective clothing to be worn if needed. As there is no European guideline to calculate the incident arc energies, the specialist electrical engineering consultants refer to the US developed calculator IEEE 1584 to determine the incident energy level and appropriate protective measures.

Specialist Electrical Engineering Organisations:
There are various specialist electrical engineering organisations which will carry out technical and consultancy services including a full arc flash study and calculating the incident arc energy:

If you wish us to assist you in contacting these organisations, please contact us for more information.


EA Technology is a specialist technology company with a world-class reputation for delivering innovative products, services and consultancy to companies which supply, distribute and use electrical energy. The company was originally the R&D centre for the UK electricity industry but now operates as a fully independent commercial company providing expert knowledge and practical solutions through our extensive team of professional engineers and consultants.

Their consultancy business provides a wide range of specialist electrical safety related services, which include the following:


  • Network analysis and fault level studies
  • Protection system design and grading studies
  • Electrical safety audits
  • Arc flash hazard studies
  • Incident energy calculations
  • Risk assessments
  • Safety Rules review
  • Operational and maintenance procedures
  • Training and mentoring

Their goal is to provide a complete professional engineering service to ensure that the electrical systems and work practices of our customers meet the highest levels of safety and industry best practice.

During the last few years they have worked with numerous utility and industrial customers concerning arc flash hazards posed by their electrical equipment and operations. Their approach is based on the principle of carrying out suitable and sufficient risk assessment, which is the cornerstone of UK safety legislation. They recommend a hierarchy of measures to eliminate, reduce, isolate and control the risks before considering the requirement for PPE. Providing all other reasonably practicable measures have been taken to minimise the risk, they consider that wearing appropriate FR clothing can play a role in reducing the wearer’s exposure to the thermal effects of an arc flash in the event that an incident should occur.

Electrical Safety UK takes the same approach to electrical arc flash and offers a full range of specialist consultancy, training & coaching and equipment supply services including:


  • Provide expert advice in general electrical safety on site or in factory premises.
  • Bespoke safety rules specific to your operation.
  • Live working risk assessments and arc Flash hazard calculations.
  • Train your staff & contractors to your procedures and rules.
  • HV & LV operational; coaching and training.
  • Cable Jointing & Electrical Fitting; coaching and training.
  • Electrical design, protection and fault location training.
  • Advise and supply electrical safety equipment, instruments and tools.
  • Carry out periodic audits and site assessments.
  • Manage authorisations, competency and approved equipment records.