⚡ AnythingOnline
⚡
Substation Step & Touch Voltage Limits Calculator electrical
100% Free • No Sign-Up

Substation Step & Touch Voltage Limits Calculator

Determine IEEE Std 80 tolerable step and touch voltage human safety thresholds based on crushed rock surface layer resistivity, body weight, and clearing time.

Human Body & Fault Duration

Soil & Surface Rock Layer

e.g. 2500 - 3000 Ω·m for wet crushed granite
0.10 m ≈ 4 inches standard

Tolerable Safety Thresholds

Permissible Touch Voltage (Etouch)
-- V
-- evaluation
Permissible Step Voltage
-- V
1 meter pace limit
Surface Derating Factor Cs
--
-- Ω·m effective
Reflection Factor K: --
Body Resistance Standard: 1000 Ω (Hand-to-Foot)
Touch Voltage Safety Margin: --
High-resistivity crushed rock (3-4 inches) adds crucial series contact resistance under personnel feet, dramatically increasing tolerable touch voltage limits.

Frequently Asked Questions

What is the difference between step voltage and touch voltage?

Touch voltage is the potential difference between a grounded metallic structure and the surface feet of a person touching that structure (assumed 1 meter horizontal reach). Step voltage is the surface potential difference between a person’s two feet spaced 1 meter apart without touching any grounded equipment.

Why is tolerable step voltage always higher than touch voltage?

In a touch voltage event, current passes from the hand through the chest, heart, and lungs into the feet, creating an extreme risk of ventricular fibrillation. In a step voltage scenario, current passes foot-to-foot across the legs with only a minor fraction reaching the heart, resulting in higher safe voltage limits.

Why does crushed rock gravel increase human safety in substations?

Crushed rock (such as granite or basalt) has a high electrical resistivity when clean and washed (2,500 to 5,000 Ω·m). It acts as a high-resistance electrical insulator in series with the human body, drastically limiting the body current that can flow into the feet.