Touch and step
Body current from touch voltage (1000 Ω body)
- where
- body current (shown in mA)
- touch voltage (V)
- body impedance, 1000 Ω simplification (Ω)
- additional series resistance of footwear and contact (Ω)
Explain this equation
Estimates the current through a person touching earthed metalwork at a given touch voltage, useful for explaining risk or comparing with IEC 60479-1 time–current zones.
UT is the touch voltage, ZB the body impedance and Ra any extra resistance in series, mainly shoes and the contact between feet and ground. ENA TS 41-24 takes 4 kΩ per shoe and about 3ρ per foot contact.
It is Ohm's law around the shock circuit. The 1000 Ω body impedance is the usual simplification; IEC 60479-1 shows the real value depends on voltage, current path, contact area and moisture.
233 V across 1000 Ω gives 233 mA; adding 2150 Ω for shoes on soil reduces it to about 74 mA. Doubling the touch voltage doubles the current.
Watch out: whether a current is dangerous depends on how long it flows; check against the IEC 60479-1 curves or use the permissible voltage limits.
Estimates the current through a person from a touch voltage, using a fixed body resistance plus any series resistance of shoes and ground contact.
Enter your values to see the result.
Good to know
1000 Ω is the simplified hand-to-feet body resistance used by IEEE 80 and often quoted from IEC 60479-1. In IEC 60479-1 the real body impedance depends on touch voltage, current path, contact area and moisture, and falls as voltage rises; for a share of the population it is below 1000 Ω at HV touch voltages, so this simplification can underestimate current. ENA TS 41-24 assumes 4 kΩ per shoe plus 3ρ per foot contact; for shoes on 100 Ω·m soil the series total is 2150 Ω.
Common mistake
Comparing the result with a fixed “safe” current without the duration. Fibrillation risk depends on both current and time (IEC 60479-1 Figure 20, curves c1–c3).
Limits
Linear resistive model with a constant body impedance (IEC 60479-1 simplification, not its voltage-dependent impedance tables). Does not assess fibrillation probability; use BS EN 50522 or IEEE 80 limits for design.
Sources
- IEC 60479-1:2018 Effects of current on human beings and livestock, Part 1: General aspects
- IEEE Std 80-2013 Guide for Safety in AC Substation Grounding
- ENA TS 41-24 Issue 2 Guidelines for the design, installation, testing and maintenance of main earthing systems in substations (consultation text, Tables 1 and 2)
For competent high-voltage engineers. Results are calculations from the published methods shown and depend entirely on the data you enter. They are not a substitute for a system study, manufacturer data, the applicable standards and Engineering Recommendations, or your organisation’s safety rules. Never use a result to justify working on or near live HV equipment.