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Basic Insulation

Insulation to provide basic protection against electric shock. The standard defines levels of insulation required in terms of constructional requirements (creepage and clearance distances) and electrical requirements (compliance with electric strength tests) . Basic insulation is considered to be shorted under single fault conditions. The actual values required depend on the working voltage to which the insulation is subjected, as well as other factors.

Bounding Surface

The outer surface of the electrical enclosure, considered as though metal foil were pressed into contact with accessible surfaces of insulating equipment.

Class I

Equipment where protection against electric shock is achieved by:

a) using basic insulation, and also

b) providing a means of connecting to the protective earthing conductor in the building wiring those conductive parts that are otherwise capable of assuming hazardous voltages if the Basic Insulation fails.

Equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions, such as double insulation or reinforced insulation, are provided, there being no reliance on either protective earthing or installation conditions.

Clearance

The shortest distance between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured through air.

Creepage Distance

The shortest path between two conductive parts, or between a conductive part and the bounding surface of the equipment, measured along the surface of the insulation.

Decorative Part

A part of the equipment, outside the enclosure, which has no safety function.

Detachable Power Supply Cord

A flexible cord, for supply purposes, intended to be connected to the equipment by means of a suitable appliance coupler.

Direct Plug-In Equipment

Equipment that is intended to be used without a power supply cord; the mains plug forms an integral part of the equipment enclosure so that the weight of the equipment is taken by the socket-outlet.

Double Insulation

Insulation comprising both basic insulation and supplementary insulation.

Electrical Enclosure

A part of the equipment intended to prevent contact with parts at hazardous voltage or hazardous energy levels.

Fire Enclosure

A part of the equipment intended to minimize the spread of fire or flames from within.

Flammability Class

The classification of the ignition and burning resistance characteristics of materials other than metal or ceramic.

Functional Insulation

Insulation needed for the correct operation of the equipment.

Hand-held Equipment

Movable equipment, or a part of equipment, that is intended to be held in the hand during normal use.

Hazardous Energy Level

A stored energy level of 20J or more, or an available continuous power level of 240 VA or more, at a potential of 2V or more.

Hazardous Voltage

A voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.

Limited Current Circuit

A circuit which is so designed and protected that , under both normal conditions and a likely fault condition, the current which can be drawn is not hazardous.

Mechanical Enclosure

A part of the equipment intended to prevent injury due to mechanical and other physical hazards.

Moveable Equipment

Equipment which is either

- 18 kg or less in mass, and not fixed, or

- equipment with wheels, castors or other means to facilitate movement by the operator as required to perform its intended use.

Normal Load

The mode of operation which approximates as closely as possible the most severe conditions of normal use in accordance with the manufacturer's operating instructions.

Non-Detachable Power Supply Cord

A flexible cord, for supply purposes, fixed to or assembled with the equipment.

NRTL

National Recognized Test Laboratory - a laboratory accredited by OSHA, the US Occupational Safety and Health Administration.

Operator

Any person, other than service personnel.

Operator Access Area

An area to which, under normal operating conditions, one of the following applies:

 - access can be gained without the use of a tool, or

 - the means of access is deliberately provided to the operator, or

 - the operator is instructed to enter regardless of whether or not a tool is needed to gain access.

Permanently Connected Equipment

Equipment which is intended for connection to the building installation wiring using screw terminals or other reliable means.

Pluggable Equipment Type A

Equipment which is intended for connection to the building installation wiring via a non-industrial plug and socket-outlet or a non-industrial appliance coupler, or both.

Pluggable Equipment Type B

Equipment which is intended for connection to the building installation wiring via an industrial plug and socket-outlet or an appliance coupler, or both, complying with IEC 60309 or with a comparable national standard.

Pollution Degree

  - Pollution Degree 1 for components and assemblies which are sealed so as to exclude dust and moisture.

 - Pollution Degree 2 generally for equipment covered by the scope of IEC 60950.

 - Pollution Degree 3 where a local internal environment within the equipment is subject to conductive pollution or to dry non-conductive pollution which could become conductive due to expected condensation.

Primary Circuit

An internal circuit which is directly connected to the external supply mains or other equivalent source (such as motor-generator set) which supplies electric power.

Rated Current

The input current of the equipment as declared by the manufacturer.

Rated Frequency

The primary power frequency as declared by the manufacturer.

Rated Voltage

The primary power voltage (for three-phase supply, the phase-to-phase voltage) as declared by the manufacturer.

Reinforced Insulation

A single insulation system which provides a degree of protection against electric shock equivalent to double insulation under the conditions specified in this standard.

Safety Critical

A component which affects the safety of the equipment. All components in primary circuitry are safety critical. Other components which protect the equipment under normal and fault conditions, such as thermal switches, optocouplers, etc. are also safety critical.

Secondary Circuit

A circuit which has no direct connection to primary power and derives its power from a transformer, converter or equivalent isolation device, or from a battery.

SELV Circuit (Safety Extra Low Voltage)

A secondary circuit which is so designed and protected that, under normal and single fault conditions, its voltages do not exceed a safe value.

Service Personnel

Persons having the appropriate technical training and experience necessary to be aware of the hazards to which they are exposed in performing a task and of measures to minimise the danger to themselves or other persons.

Supplementary Insulation

Independent insulation applied in addition to basic insulation in order to ensure protection against electric shock in the event of failure of the basic insulation.

Telecommunication Network

A metallically terminated transmission medium intended for communication between equipments that may be located in separate buildings, excluding:

 - the mains system for supply, transmission and distribution of electrical power, if used as a telecommunication transmission medium; and

 - TV distribution systems using cable; and

 - SELV circuits connecting units of data processing equipment

TNV Circuit

A circuit in the equipment to which the accessible area of contact is limited and that is so designed and protected that, under normal operating and single fault conditions, the voltages do not exceed specifying limiting values.

TNV-1 Circuit

A TNV circuit

- whose normal operating voltages do not exceed the limits for a SELV circuit under normal operating conditions

- on which overvoltages from telecommunication networks are possible

TNV-2 Circuit

A TNV Circuit

- whose normal operating voltages exceed the limits for a SELV circuit under normal operating conditions

- which is not subject to overvoltages from telecommunication networks

TNV-3 Circuit

A TNV Circuit

- whose normal operating voltages exceed the limits for a SELV circuit under normal operating conditions

- on which overvoltages from telecommunication networks are possible

Tool

A screwdriver or other object which may be used to operate a screw, latch or similar fixing means.

Touch Current

Electric current through a human body when it touches one or more accessible parts. (Touch current was previously included in the term 'leakage current').

Working Voltage

The highest voltage to which the insulation under consideration is, or can be, subjected when the equipment is operating at its rated voltage under conditions of normal use.

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