Touch Voltage / Step Voltage Calculator

Touch voltage is the potential difference between a grounded metallic structure and a point on the earth's surface where a person might be standing. Step voltage is the potential difference between two points on the ground surface separated by a distance of one human step (typically 1 meter).

The choice depends on the population you're protecting. 50 kg represents a lighter person (including children), providing more conservative safety limits. 70 kg represents an average adult. Use 50 kg for public areas or when maximum safety is required.

Shock duration is typically the fault clearing time of protective devices. Common values are 0.5 seconds for fast protection systems, 1.0 second for standard systems, or up to 3 seconds for slower backup protection. Shorter durations allow higher safe voltage limits.

Soil resistivity should be measured on-site using specialized equipment. Typical values range from 10 Ω·m for wet clay to 10,000 Ω·m for dry sand or rock. Surface layer materials like gravel typically have much higher resistivity (1000-5000 Ω·m).

Include a surface layer when the site has added materials like crushed rock, gravel, concrete, or asphalt over the natural soil. These materials typically have higher resistivity and can improve safety by increasing body resistance.

The calculator uses IEEE Std 80 equations for touch and step voltage limits. Touch voltage limit = (1000 + 6Cs×ρs) × √(ts/Ib), where Cs is surface layer factor, ρs is surface resistivity, ts is shock duration, and Ib is body current limit.

The calculated limits represent maximum safe voltages during ground fault conditions. Your grounding system must be designed so that actual touch and step voltages during faults remain below these calculated safe limits to protect personnel.