Principles of electrical safety:Precautions against arc and flashover burn injuries

Precautions against arc and flashover burn injuries

Most arc and flashover burn injuries occur during live work on electrical systems. To avoid the hazard, work should be done whenever possible on apparatus that has been made dead and isolated. If this is not possible then only competent people should undertake the work and precautions must be taken to minimize the risk. Depending upon the particular circumstances, these may include the use of:

● insulating screens or barriers between live parts of different polarity and between live parts and earthed metalwork

● insulated tools

● test equipment probes on which only the contact points are bare, with a maximum length of exposed metal of 4 mm, and the rest of the probe is insulated. The leads should have protection against short-circuit current, such as integral fuses or current-limiting features in the test equipment

● personal protective equipment, such as insulating gloves, and heat-resistant face shields and clothing

Precautions against fire

The main precautions against fire of electrical origin are as follows:

● each cable must have sufficient current carrying capacity for the load current and must be protected by an excess current protective device (fuse or circuit breaker) with tripping value set to be below the cable’s maximum current carrying capacity

● fuses and circuit breakers must be rated for the system fault level

● devices with the potential for creating overload conditions, such as motors, should be protected by excess current protective devices

● system components must be selected and appropriately protected for use in the prevailing environmental conditions to prevent degradation that may lead to insulation failure

● the electrical system must be subject to routine preventive maintenance to detect degradation or failures that may otherwise lead to fire.

Enhanced protection against fire and its effects can also be obtained by using cables that have low smoke and fume emission properties; more information on these cables is provided in section 9.2.5.

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