FOCUS
Transmission risks
The dangers are well known to regulators. IEC 60364-4-42: 2010 (clause 422.3.9) makes it mandatory to install highly sensitive residual current devices (RCDs) in locations of increased fire risk. In the UK, BS 7671: 2018: Requirements for Electrical Installations. IET Wiring Regulations requires installations to have RCD protection provided by a tripping current that does not exceed 300mA wherever an increased fire risk exists. Using new technology, organisations
are now able to choose circuit breakers with earth leakage protection and tripping capabilities in which the circuit is broken when the earth leakage current passes above a certain threshold. Another option is a circuit breaker with earth leakage that sends an alarm to operators when the earth leakage threshold is breached, thus maintaining continuity of supply but warning of an impending fault that requires action. Earth leakage circuit breakers can be used
instead of traditional overcurrent only breakers at no additional footprint, while increasing safety. The option of just enabling an alarm instead of tripping can also avoid disruptions by limiting downtime.
Arc flashes
When a short circuit occurs between the live parts of a system, the current travels through the air or nearby gases. This releases a large amount of energy in a fraction of a second,
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taking the form of heat, sound, light and pressure waves. This type of fault, normally described as an ‘arc flash’, poses a significant fire risk. Personal protective equipment is crucial for
workers where arc flashes are involved, but faster acting devices are also crucial to mitigating them in the first place, enhancing safety. To reduce the severity of arc flash hazards to which workers are exposed, arc flash energy levels must themselves be reduced. Optical relays that detect the presence
of arcing faults by looking for the associated flashes of light and irregular current flow are strongly advised. These relays will then activate a circuit breaker or an even faster shorting switch which creates a bolted fault that clears the arc. Another method is to use a maintenance
selector switch to temporarily lower the instantaneous short circuit current setting. Should an arc flash occur downstream, the reduced fault clearing time allows a decrease in the amount of energy generated by the electrical arc and can limit the risk of injury.
Lightning strikes
While often an extreme case, a lightning strike is a real possibility in most parts of the country. Each year, the UK, Ireland and the surrounding seas receive 200,000 to 300,000 lightning counts a year. On average, two people are killed and 30 injured each year due to lightning strikes, which often result in devastating fires.
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