Which protection classes are used for electrical equipment?

The IEC/EN 61140 standard classifies electrical equipment according to its safety with regard to shock currents and electric shocks. Depending on its design features, equipment is assigned to the following protection classes:

• Protection class 0:
  No protection. Devices of this kind are not permitted in the European Union.
• Protection class I:
  Device with a connection to an earthing conductor and basic insulation between accessible components and the earthing conductor. A proper connection to the earthing conductor is mandatory.
• Protection class II:
  Device with double or reinforced insulation between accessible components and components that are dangerous to touch. These devices do not have the option of connecting to an earthing conductor.
• Protection class III:
  Device that is supplied by a separated extra-low voltage (SELV) circuit or a protective extra-low voltage (PELV) circuit and which does not generate voltages that are higher than those permitted for SELV and PELV circuits.

PULS switch-mode power supplies are generally designed to comply with protection class I.