Arc Flash Training: Risks in low voltage installations
Our clients working with high voltage electrical installations are typically well aware of the dangers posed by arc flash. The explosion caused by a high fault current in a conductor can discharge plasma at more 19,000 °C, together with blast shrapnel and molten metal. The implications for personnel, even those several metres away from the site of the arc, can include life changing or even fatal injuries.
Far less well understood, however, is that arc flash risks are often present in low voltage (LV) installations too – including power supply equipment used in a factory, data centre or commercial building. In an analysis of more than 6,000 distribution and switchboards at lower voltages at a variety of industrial sites, we found that almost a quarter presented risks of NFPA 70E electrical safety standards Category 3 or higher. 6.5% were in the ‘Dangerous’ category where personal protective equipment (PPE) alone will not provide adequate protection to personnel.
There is a common misconception that system impedances such as transformers etc. can reduce arc flash hazards on LV systems to a low level. However, even a small 1MVA distribution transformer can produce a short circuit fault current on the secondary side, typically in the order of 20-30kA, a substantial value when considering arc flash hazards.
It should also be noted that such LV installations can often be accessed and operated by persons with minimal arc flash training and who are less familiar with the potential of an incident than those who are trained and qualified to operate high voltage equipment – where access is much more likely to be controlled. Consequently, such personnel could be considered at greater risk than those who regularly operate high voltage equipment.
Calculating arc flash risk is a specialist task. The potential severity of an arc flash event depends on the configuration of the entire electrical system at a site, along with knowledge of system fault currents and protection clearance times. Specialist software is usually required to make the necessary calculations.
In any system, the likelihood of an incident depends on the condition of the equipment and the way it is operated. This leads on to the concept of a risk assessment, an area of study that is coming more to the fore in terms of both HV and LV equipment.
GSE systems can help you understand and manage arc flash risk at your sites. Our services include comprehensive system modelling and risk analysis in accordance with IEEE 1584, and recommendation of appropriate mitigation strategies, including the review of the system design, the installation of arc fault detection relays and other equipment and methodologies designed to protect operators from arc flash energy.
We can also assist with the implementation of your risk reduction strategy, including a switchboard risk assessment, the installation of equipment, appropriate labelling and the provision of electrical safety training for operations and maintenance staff. Our engineers are involved in carrying out switchgear risk assessments for various clients around the world, typically considering the requirements of HSG85 and HSG230.