There have been an increasing number of touch potential incidences reported during switching of electrical equipment in systems where no faults were present. These touch potentials occurred during closing and opening of circuit breakers and contactors.
A mechanism has been identified for these touch potential transients that is consistent with the reported incidences. The estimated effect of these transients, based on modelling of the mechanism for each incidence, 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.
This paper describes the transient touch potential mechanism and the methods developed to reduce the effect so they are not perceivable, ensuring safe operation under all conditions. The result is guidance on the safe use of switchgear to reduce or eliminate touch potential transients.