Definitions
Electric Shock: Physiological effect resulting from an electric current passing through a human or animal body ( see also shock current ).
Shock Current: A current passing through the body of a person or animal and having characteristics likely to cause physiological effects.
Danger: Risk to health, life or limb from shock, burn, or injury from mechanical movement of electrically driven equipment or from fire, attendant upon the use of electrical energy.
Flammable: Capable of being easily ignited.
Basic Insulation: Insulation applied to live parts to provide basic protection against electric shock.
Note 1: Basic insulation will normally need supplementary measures in order to complete the protection against electrical shock.
Double Insulation: Insulation comprising both basic safety insulation and supplementary insulation.
Note: See also Class II equipment
Reinforced Insulation: A single insulation system applied to live parts, which provides the same degree of protection against electric shock as double insulation.
Earth: The conductive mass of the earth, the electric potential of which at any point is conventionally taken as equal to zero.
Conductive Part: A part capable of conducting current but not necessarily used for carrying service current.
Exposed Conductive Part: A conductive part of electrical equipment, which can be touched and is not normally live but may become live under fault conditions.
Note: A conductive part of electrical equipment, which can only become live under fault conditions through an exposed conductive part, is not considered to be an exposed conductive part for the purposes of the se Rules.
Extraneous Conductive Part: A conductive part, not forming part of the electrical installation, liable to introduce a potential, generally the earth potential.
Note: Examples are:
· structural metal work of a building,
· metallic gas pipes, water pipes and heating tubes, etc.,
· non-electrical apparatus ( radiators, gas or coal-fired cooking ranges, metal sinks etc .)
Fault: Contact of a live part with exposed or extraneous conductive parts, which is caused by accident or failure of insulation.
Fault Current: A current resulting from an insulation failure or the bridging of insulation.
Protective Conductor ( symbol PE ): A conductor required for certain measures of protection against electric shock, which electrically connects any of the following parts:
· Exposed conductive parts
· Extraneous conductive parts
· Main earthing terminal
· Earthed point of the source or artificial neutral
Earth-Fault Current: A fault current that flows to earth either directly or through a protective conductor.
Earth Leakage: ( see Leakage Current )
Leakage Current ( in an installation ): A current that flows to earth or to extraneous conductive parts in an electrically undamaged circuit.
Note: This current may have a capacitive component including that resulting from the deliberate use of capacitors.
Arm’s Reach: A zone extending from any point on a surface where persons usually stand or move about, to the limits, which a person can reach with the hand in any direction without assistance.
Simultaneously Accessible Parts: Conductors or conductive parts that can be touched simultaneously by a person or, where applicable, by livestock.
Note: Simultaneously accessible parts may be:
· Live parts.
· Exposed conductive parts.
· Extraneous conductive parts.
· Protective conductors
· Earth electrodes.
Touch Voltage: Voltage appearing between simultaneously accessible parts, during an insulation fault.
Note 1: By convention, this term is used only in connection with protection against indirect contact.
Note 2: In certain cases, the values of the touch voltage may be appreciably influenced by the impedance of the person in contact with these parts.
Direct Contact: Contact of persons or livestock with live parts.
Barrier: A part providing protection against direct contact from any usual direction of access.
Obstacle: A part preventing unintentional direct contact, but not preventing direct contact by deliberate action.
Indirect Contact: Contact of persons or livestock with exposed conductive parts or extraneous conductive parts, which have become live under fault conditions.
Class I Equipment: Equipment having basic insulation throughout, and depending on the earthing of exposed conductive parts for protection against indirect contact in the event of failure of the basic insulation.
Class II Equipment: Equipment having double insulation or reinforced insulation, or a combination of these throughout, and whose intermediate parts are protected by supplementary insulation so that there is no risk of indirect contact in the event of failure of basic insulation.
Note: Class II equipment is marked with the symbol shown in Figure 1.
Supplementary Insulation: Independent insulation provided in addition to the basic safety insulation in order to ensure protection against electric shock in the event of failure of the basic safety insulation ( usually associated with Class II equipment ).
Design Current ( of a circuit ): The current intended to be carried by a circuit in normal service.
Rated Current ( of a circuit ): The maximum value of current for which the circuit is intended.
Current Carrying Capacity ( CCC ) (of a conductor ): The maximum current that can be carried continuously by a conductor under specified conditions without its steady-state temperature exceeding a specified value.
Fuse: A device that, by the fusing of one or more of its specifically designed and proportioned components, opens the circuit in which it is inserted by breaking the current when this exceeds a given value for a sufficient time. The fuse comprises all the parts that form the complete device.
Rated Current ( of a protective device ): The value of current for which the operating conditions of the protective device are determined.
Note: For adjustable protective devices, the current setting is considered to be rated current.
Fusing Current: The minimum value of current flowing through a fuse, which will cause the fuse to interrupt that current in stated conditions.
Overcurrent: Any current exceeding the rated value. For conductors, the rated value is the current-carrying capacity.
Overload Current ( of a circuit ): An overcurrent occurring in a circuit in the absence of an electrical fault.
Short Circuit Current: An over-current resulting from a fault of negligible impedance between live conductors having a difference in potential under normal operating conditions.
Prospective Short Circuit Current : The value of short-circuit current that would flow if the current-limiting device were replaced by a conductor of negligible impedance.
Breaking Capacity: A value of current that a protective device is capable of breaking at a specified voltage and under prescribed conditions of use and operation.
Switch (mechanical): A mechanical switching device capable of making, carrying and breaking currents under normal circuit conditions, which may include specified operating overload conditions and also carrying for a specified time currents under specified abnormal circuit conditions, such as those of a short-circuit.
Circuit Breaker: A mechanical device capable of making, carrying and breaking currents under normal circuit conditions and also capable of making, carrying for a specified time, and breaking currents under specified abnormal circuit conditions, such as those of short circuit.
Residual Current: The algebraic sum of the instantaneous values of current flowing through all live conductors of a circuit at a point.
Residual Current Device
( RCD ): A mechanical switching device intended to disconnect a circuit when the residual current attains a stated value under specific conditions.
Residual Current-Operated Circuit-Breaker
( RCCB ): A mechanical switching device designed to make, carry and break currents under normal service conditions and to cause the opening of the contacts when the residual current attains a stated value under specified conditions.
Residual Current-Operated Circuit-Breaker with Integral Overcurrent Protection
( RCBO ): A residual current-operated circuit-breaker designed to perform the functions of protection against overloads and / or short-circuits.
Residual Operating Current: Residual current value that causes the residual current device to operate under specified conditions. ( Values range from 10mA to 500mA ).