Control of Transient Touch Voltages During Switching

There have been an increasing number of electric shock incidents reported during switching of electrical equipment in systems where no faults were present. These electric shocks occurred during closing or opening of circuit breakers or contactors. A mechanism has been identified for transient touch voltages leading to electric shocks that is consistent with the reported incidents. The estimated effect of these transients, based on modelling of the mechanism for each incident, ranged from perceivable to extreme pain. Fortunately, none reached the level for which fibrillation may occur according to AS/NZS 60479.2. However, the possibility of secondary effects, such as injury from falling, cannot be understated. An ACARP funded project has allowed further research into these transient touch voltages. This included the development of a hardware simulation to generate these transients in a controlled environment in the laboratory. Furthermore, the hardware simulation has allowed for the development and testing of a solution to reduce these touch voltage transients such that they are unlikely to be perceptible. This paper describes how transient touch voltages are generated and the solution developed to reduce these touch voltage transients, so they are unlikely to be perceivable, ensuring safe operation under all conditions.