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Classes of Protection for Electrical Equipment
Classes of Protection for Electrical Equipment
Classes of Protection Electrical equipment is divided in protection classes 0, I, II and III. These classes of protection are defined by the method in which the protection against electric shock is achieved (IEC 61140). Programmable Logic Controllers and their peripherals must correspond with protective classes I, II or III (according to IEC 61131-2).
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Protective Class 0 Electrical equipment for which the protection against dangerous body currents only contacts the basic insulation belongs to protective class 0. This means that no medium for connecting conductive components to the protective conductor (ground conductor) is provided in the permanent wiring of the system. If the basic insulation fails then the surrounding environment is trusted.
Protective Class I Electrical equipment for which the protection against dangerous body currents does not only contact the basic insulation belongs to protective class I. An additional contact for connecting conductive components to the protective conductor (ground conductor) is provided in the permanent wiring of the system. Components that can be touched are voltage-free if the basic insulation fails in this case.
Protective Class II Electrical equipment for which the protection against dangerous body currents does not only contact the basic insulation belongs to protective class II. An additional safety feature such as doubled insulation or reinforced insulation is provided but no protective ground.
Protective Class III Electrical equipment for which the protection against dangerous body currents is achieved by safety extra-low voltage (SELV) supply belongs to protective class II. In this type of electrical equipment, no voltage that is higher than the SELV is produced.
SELV
SELV (Safety extra-low voltage): is defined as a voltage that, measured between conductors or between a conductor and ground, does not exceed 42.4 V peak or constant voltage. The circuits in which these are used must be separated from the power supply by a safety transformer or a similar device.
