This is the passage of current through the body of such magnitude as to have significant harmful effects. below Figure illustrates the generally accepted effects of current passing through the human body. How, then, are we at risk of electric shock and how do we protect against it?
1 mA–2 mA Barely perceptible, no harmful effects
5 mA–10 mA Throw off, painful sensation
10 mA–15 mA Muscular contraction, can’t let go
20 mA–30 mA Impaired breathing
50 mA and above Ventricular fibrilation and death
There are two ways in which we can be at risk.
1 Touching live parts of equipment or systems that are intended to be live. This is called direct contact.
2 Touching conductive parts which are not meant to be live, but which have become live due to a fault. This is called indirect contact.
The conductive parts associated with indirect contact can either be metalwork of electrical equipment and accessories (class l) and that of electrical wiring systems (e.g. metal conduit and trunking), called exposed conductive parts, or other metalwork (e.g. pipes, radiators and girders), called extraneous conductive parts.