Indirect contact electric shock

The majority of direct and indirect contact electric shock and burn accidents occur at 230 V on distribution systems or on connected equipment. There are many instances in which high voltage overhead lines are touched, so this is a form of direct contact however, they usually result in predominantly burn injuries rather than electric shock. 

Earthed equipotential bonding and automatic disconnection of supply, known as EEBADS, is the most common technique employed for protection against indirect contact electric shock. Essentially, for earth-referenced supplies, the technique requires the exposed conductive parts of Class I apparatus and equipment to be earthed by means of the protective conductor, with the protective conductor connected back to the main earthing terminal of the installation. 

From an historical perspective, in order to avoid indirect contact electric shock, the now-superseded 1966 edition of BS 638 Specification for arc welding plant, equipment and accessories, recommended that the power source metalwork and the work piece should be earthed. This was a safeguard against an interwinding fault in a transformer source causing the... 

Protective measures against direct and indirect contact (electric shock) are required depending on the battery nominal voltage and the chosen ground system of the electric network (Table 6.4). In the case of a system short circuit an effective protection can be achieved by incorporating a system with protective conductor and associated protective devices. In battery installations mainly an IT network or TN network is used. 

Two types of contact will result in a person receiving an electric shock. Direct contact with live parts involves touching a terminal or line conductor that is actually live. The regulations call this basic protection, indirect contact results from contact with an exposed conductive part such as the metal structure of a piece of equipment that has become iive as a resuit of a fauit. The regulations call this fault protection. 

OSHA has requirements for safe work practices at 1910.333. By not complying with these work practices employees performing work near or on equipment or circuits (which are or may be energized) could be exposed to electric shock or other injuries resrdting from either direct, or indirect, electrical contacts. Your company-specific safety-related work practices must be consistent with the nature and extent of the electrical hazards. 

If, for any reason, there was a breakdown of insulation in a part of an electric circuit or in any apparatus such as, say, a hand-held metal-cased electric drill, it is conceivable that current would flow external to this supply circuit, if a path were available. For example, the metalwork of the drill may be in contact with a live internal conductor at the point of insulation breakdown. Or, take the example of someone working at a switch or socket outlet from which the cover had been removed before the electricity supply had been isolated. In both circumstances the person concern could come into contact with a live part, either metalwork of the drill made live because of the internal fault condition or a live terminal exposed by removal of the cover which, if the conditions were right, would allow an electrical current to flow through the body to earth. The former is an example of electrical shock received by indirect contact whilst the latter is an example of electrical shock from direct contact. If the total resistance of the earth fault path were of a sufficiently low value, the current could kill or maim. 

Accidents involving an electric shock are usually subdivided into two categories - direct contact and indirect contact shocks. The standards that will be considered later use this distinction. A direct contact shock occurs when conductors that are meant to be live, such as bare wires or terminals, are touched. An indirect contact shock is usually associated with touching an exposed conductive part that has become live under fault conditions an example of an exposed conductive part would be the metal casing of a washing machine. 

The intention of Regulation 7 is to prevent electric shock and burn injuries from direct and indirect contact, and fire and explosion consequent on short circuits or leakage currents between circuit conductors or between circuit and other conductors. 

As indirect contact shocks are the most common form of electric shock incident, five methods of avoidance are dealt with extensively in section 413. 

Electrical protective devices are used to protect machines and equipment from damage due to values of voltage or current exceeding design levels. They are also used to protect individuals from the risk of injury, by isolating electrical faults in part of the system. Electrical hazards associated with workshop machinery and tools may be caused by overload current, short-circuit current, or electric shocks to individuals arising from direct or indirect contact with live conductors. Overload current is an excessive current... 

---