There is a mistaken belief that a short circuiting device will prevent current flow in the human body “Not so”. An Earthing and short circuiting device can only limit the current flow through the human body.
Death or serious injury is unlikely to occur if current/time values are kept under:
1,000 milliamps for 30 milliseconds (1½ cycles) or 100 milliamps for 3 seconds *
Limiting current flow in the human body to safe levels is entirely dependent on the resistance of the short-circuiting jumper. To achieve this safe current level the voltage across the human body must not exceed 100 volts.
The following calculations apply:
Resistance of jumper R = V = Voltage across Jumper = 100 Volts = 10 mOhms
I Fault current 10,000 Amps
Voltage across person/jumper V = IR = 10,000 amps x 10 mOhms = 100 Volts
Current through person I = V = Voltage across Person = 100 Volts = 100 milliamps
R Resistance of person 1000 Ohms *
TABLES FROM I.E.C. 1000-05 AND ET 213:2007
