Touch voltage is the voltage that can appear between exposed conductive parts (such as a charger enclosure, metal cabinet, or vehicle body) and the ground—or another conductive object—that a person can touch during an electrical fault or abnormal condition. It is a key safety concept in EV charging because users physically interact with chargers and connectors, often outdoors and in wet conditions.
Touch voltage is closely related to earthing, bonding, and fault protection performance.
Why Touch Voltage Matters in EV Charging
Touch voltage matters because excessive touch voltage can cause electric shock risk. In charging installations, controlling touch voltage helps:
– Protect drivers and pedestrians in public and private sites
– Ensure safe operation under fault conditions (insulation failure, conductor faults)
– Reduce risk in outdoor environments where moisture lowers body resistance
– Support compliance with electrical safety standards and site inspections
– Improve trust and reliability for public charging infrastructure
Touch voltage risk is especially important where many people can contact conductive surfaces, such as on-street chargers and metal street cabinets.
What Causes Touch Voltage
Touch voltage can occur when a fault causes part of the installation to rise above earth potential, for example:
– A live conductor contacts the charger housing due to insulation failure
– A neutral/earth fault causes potential rise in the protective conductor system
– High earth resistance in TT systems limits fault current, raising local potential
– Broken or compromised PEN conductor in TN-C-S systems (specific risk scenarios)
– Poor bonding between metallic parts, creating different potentials
– Fault current flowing through earth due to inadequate fault loop impedance
Touch Voltage vs Step Voltage
These are related but different:
– Touch voltage: voltage between a touched object and the ground (hand-to-feet path)
– Step voltage: voltage between two points on the ground a step apart (feet-to-feet path)
Both are managed through earthing design, bonding, and fault protection.
How Touch Voltage Is Controlled
EV charging installations control touch voltage through a combination of measures:
– Proper earthing system design (TN / TT / IT earthing systems)
– Reliable protective earth (PE) continuity and low-impedance fault paths
– Equipotential bonding of all accessible metalwork (charger housing, cabinets, metallic structures)
– Correct selection and testing of RCDs and overcurrent protection devices
– Additional protective measures where required (for example, approaches that address PEN integrity risk in certain TN supplies)
– Good installation practices (tight terminations, correct conductor sizing, corrosion protection)
– Regular inspection and testing (earth resistance, loop impedance, RCD trip tests)
Where Touch Voltage Risk Is Highest
Higher risk environments include:
– Outdoor public charging exposed to rain and snow
– Coastal or corrosive environments affecting earthing connections
– Sites with high earth resistance or poor soil conditions (TT challenges)
– On-street chargers near metallic street furniture and cabinets
– Installations with long cable runs or questionable bonding continuity
– Construction sites or temporary supplies
Operational Signs and Pitfalls
– Nuisance tripping or unexplained faults can indicate earthing/bonding problems
– Corroded earth connections can degrade over time and increase touch voltage risk
– Incorrect bonding between charger, cabinet, and nearby metalwork can create potential differences
– Treating earthing as “one-time commissioning” instead of a maintained safety system
Related Glossary Terms
Step Voltage
Equipotential Bonding
Protective Earth (PE)
TN / TT / IT Earthing Systems
PEN Fault Protection
RCD
Earth Resistance Test
Surge Protection Device (SPD)