Touch voltage is the potential difference between an accessible conductive part and a point a person can reach at the same moment, usually the ground about a metre away. How much is tolerable depends on duration: low-voltage rules commonly cap sustained values at 50 V AC, while substation earth grids are designed to allowable limits that rise as fault clearance gets faster. Bonding, earth grid mesh spacing and quick disconnection are the tools that keep it down.
Earth grid study shows touch voltage at the fence corner hitting 780 V on a 0.5 s fault, we need a grading ring outside the fence.
Also heard as
- touch potential
- prospective touch voltage
Related terms
Step voltage
Voltage between a person's feet across the ground surface near an earth fault or an earthed structure.
Equipotential bonding
Connecting metal parts together so they sit at one potential and no dangerous voltage appears between them.
Earth fault loop impedance
Total impedance of the path a fault current takes from the source, through an earth fault and back again.