Touch Voltage / Step Voltage Calculator

When electrical faults occur in power systems, dangerous voltages can appear at ground level — the Touch Voltage / Step Voltage Calculator determines the maximum safe voltage limits a person can be exposed to without risk of electrocution. Enter your shock duration, body weight, and native soil resistivity, then optionally enable a surface layer (gravel, concrete, etc.) with its resistivity and depth. The calculator returns your Touch Voltage Limit, along with Step Voltage Limit, Body Current Limit, and Body Resistance.

s

Duration of electrical shock exposure in seconds

Ω·m

Electrical resistivity of the natural ground material

Check if there is a surface layer material (gravel, concrete, etc.)

Ω·m

Resistivity of surface layer material if present

m

Thickness of surface layer material

Standard body weights for safety calculations

Results

Touch Voltage Limit

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Step Voltage Limit

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Body Current Limit

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Body Resistance

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Frequently Asked Questions

What is touch voltage and step voltage?

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).

Should I select 50 kg or 70 kg for body weight?

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.

What value should I enter for shock duration?

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.

How do I determine soil resistivity values?

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).

When should I include a surface layer in my calculations?

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.

What equations does the calculator use?

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.

How do these limits relate to grounding system design?

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.