Arc Flash Assessment Capability
TNEI are pleased to be able to offer arc flash assessments to our clients. Arc flash assessments are typically undertaken for electrical installations from 400V up to 11kV, for example industrial complexes.
Arc flash assessments or studies may be required when personnel work on live electrical equipment. In the event of a fault, like a dropped spanner, the resulting ‘lightning’ flash can cause serious injury. Arc flash assessments provide a method of determining the personnel protective equipment (PPE) required to protect the worker from the effects of the arc flash.
Arc Flash Calculations
The basis for an arc flash assessment is the power system data related to the calculation of fault levels and protection settings for the equipment under review. Currently fault calculations are undertaken according to the US ANSI C37 standard.
Once these values are known the arcing current that will flow in a fault can be determined and hence the operating time of the protection devices calculated. The nominal incident energy can then be calculated. This is a function of the current and protection operating time. Lower fault currents give longer operating times and possibly higher incident energies.
Once the nominal incident energy is determined, the likely working distance between the personnel and the equipment is determined. This working distance, together with the incident energy, is used to calculate the received incident energy. The category of PPE is then identified.
The IEEE calculations make use of various assumptions and factors to take account of the different environments and nature of arcing faults. These calculations are typically undertaken using specialist power system software.
Arc Flash History
Arc flash calculations started in the US from efforts to reduce the number of electrical flashover related incidents. Following extensive research on the energy contained in electrical arcs the American National Fire Protection Association (NFPA) and the Institute of Electrical and Electronic Engineers (IEEE) have produced a generally accepted approach for arc flash assessments. IEEE Std.1584 (aka IEEE 1584) and NFPA70E are the resulting standards. These standards recommend a method to determine the estimated energy released by an arc on a piece of electrical switchgear - this is an 'arc flash assessment’.
The activity in the US has not gone unnoticed and the issue has been highlighted to various bodies in the UK. In line with the risk-assessment based approach for work management, it has been suggested that arc flash assessments should form part of the data input into the risk assessment for the switchgear and its operation. Currently there are no UK specific standards or legislative amendments to incorporate the requirement. Instead health and safety legislation requires a 'suitable and sufficient' risk assessment to be undertaken.