Safety class

Electrical installations and electrical devices must provide sufficient protection against electric shock (direct contact with live components) for people and animals. This protection can be achieved by means of

  • covers or claddings;

  • obstructions (e.g. barriers) and distance;

  • additional protective devices e.g. fault-current circuit breakers (see also chapter 2.1.9.5.2);

  • insulation of active (live) components; and

  • operation with safety extra-low voltage that is harmless in case of contact.

According to the level of protection against excessive voltage in case of direct contact, electrical equipment such as luminaires is classified into three safety classes according to EN 61140 (formerly DIN VDE 0140) and CENELEC HD 366:

a

In safety class I, the protection objective is achieved by insulating live components (referred to as basic insulation) and by connecting exposed conductive metal components to the protective conductor. The protective conductor’s connection terminal is marked with the earthing symbol.

If the basic insulation fails and leads to an electrical connection of the voltage source with exposed luminaire components, current flows through the protective conductor. The protective conductor is connected to the earth potential to prevent luminaire components connected to it from consuming hazardous shock voltages.

In addition, fault-current circuit breakers (residual current operated device, RCDs) disconnect electrical equipment from the supply network if the residual or fault current flowing in the protected circuit is excessive.

Figure 2.48: TN system with RCD

Circuits with sockets must be equipped with circuit breakers triggered at 30 mA. This serves to ensure that shock current is limited to 30 mA in case of contact with live components even without a connection to the protective conductor and cannot cause permanent health damage.

M

In safety class II electrical equipment, live components are equipped with additional protective insulation beyond basic insulation. Connection to the protective conductor is not required. Installation-specific protective measures are not necessary. The device is labelled with a double square.

In safety class III devices, the protection is provided by the application of safety extra-low voltage (SELV). This means that the supply voltage must not exceed 50 V (AC) or 120 V (DC) in connection with a safety transformer (or equivalent device).