Step voltage is the voltage difference a person could experience between their two feet when standing on the ground during an electrical fault. It occurs when fault current flows into the earth (for example from a damaged cable, faulty equipment, or lightning event), creating a voltage gradient across the ground surface. If your feet are at two points with different earth potentials, current can pass through your body.
Step voltage is a key safety concept in earthing (grounding) design for electrical infrastructure, including EV charging sites.
Why Step Voltage Matters in EV Charging Installations
EV chargers are often installed outdoors in public or semi-public areas—car parks, streets, depots—where people may be close to electrical equipment and earthing systems. Step voltage risk increases when:
– A fault energizes metalwork or an earthing electrode system
– There is high fault current and the ground has high resistance (dry soil, asphalt areas)
– People can stand near an earthing point during a fault
– Chargers are installed with concrete foundations or metal structures connected to earth
Proper design reduces the chance that a fault creates hazardous touch and step voltages around the charger location.
Step Voltage vs Touch Voltage
Step voltage and touch voltage are related but different:
– Step voltage is measured between two points on the ground a step apart (foot-to-foot)
– Touch voltage is measured between a grounded surface (your feet) and a conductive object you touch (hand-to-foot), such as a charger enclosure, bollard, or metal post
In many outdoor installations, touch voltage is often the higher risk because it can drive current through a larger portion of the body, but step voltage is still a critical design factor.
When Step Voltage Becomes a Risk
Step voltage hazards typically occur during abnormal conditions:
– Earth faults on LV systems (cable damage, insulation failure)
– Faults in nearby distribution equipment feeding the chargers
– Broken neutral or earthing issues that shift potentials
– Lightning strikes or surge events affecting earthing systems
The hazard is usually time-limited but can be severe if protective devices do not clear the fault quickly.
How Step Voltage Risk Is Reduced
Mitigation measures focus on controlling earth potential rise and the surface voltage gradient:
– Design effective earthing and equipotential bonding so metalwork stays at the same potential
– Ensure protective devices disconnect faults quickly (appropriate OCPD selection and coordination)
– Use RCDs and fault protection suited to EV charging circuits
– Install insulating or high-resistance surface layers (asphalt, rubber mats, crushed rock) where relevant
– Use earthing grids, rings, or multiple electrodes to spread fault current and reduce gradients
– Keep the public away from earthing hotspots using layout planning and barriers where needed
EV charging projects often include an earthing study as part of the electrical design, especially for larger sites and public infrastructure.
Where Step Voltage Is Considered in EV Charging
Step voltage checks may be relevant for:
– Public charging hubs with many circuits and high fault levels
– Charger islands with metal structures and bollards
– Sites with separate earthing electrodes near pedestrian areas
– Depots and industrial sites with high prospective fault current
– Installations near substations or LV distribution cabinets
Practical Design Notes for Project Teams
– Step voltage is influenced by soil resistivity, electrode geometry, and fault magnitude
– Civil design matters: foundations, rebar bonding, and surface finishes can affect safety outcomes
– Documentation should include earthing layout, bonding points, and inspection/maintenance access
– Verification tests may be required during commissioning, depending on local standards and site risk
Related Glossary Terms
Touch Voltage
Earthing / Grounding
Equipotential Bonding
Protective Earth (PE)
Residual Current Device (RCD)
Overcurrent Protection Device (OCPD)
Prospective Fault Current
PME Fault Protection