Why 50 volts?
- The typical body has a contact resistance of 500 ohms at the point of contact with the electrical source.
- The body has an internal resistance of approximately 100 ohms.
- Touch/Step potential to ground of about 5000 ohms (Ω is the symbol for ohms).
- Combine the resistances to find the total resistance
500Ω + 100Ω + 5000Ω = 5600 Ω
To find the amount of current the body is subjected to when in contact with 120V electrical source:
- 50v / 5600 Ω = 8.9 mA
- 120v / 5600 Ω = 21 mA
- It is around 10 mA that the "cannot let go" level is reached. Once muscle lock-up occurs, exposure time is amplified and the probability of electrocution increases dramatically.
Figure 1: The Human Body is Conductive
Figure 2: Effects of Electric Shock on the Body