Portable Appliance Testing - Class of Construction

Class of Construction

Electrical appliance classes are differentiated by a series of IEC protection classes. The protocols for PAT Testing vary by appliance class.

  • Class I – Single insulated wiring, which requires an earth connection. There is no symbol for a Class I product so if a rating plate has no symbol on it then it is usually Class I.
  • Class II – Double insulated wiring, The earth clamp is still connected during the insulation test even though no earth on appliance. Class II is indicated by double box.
  • Class III – These are appliances that are supplied at a low voltage (usually called Separated Extra Low Voltage) which must be less than 50 V. These appliances are supplied with a transformer supply that is also marked.

The earth lead is connected to metal parts on both Class I and Class II appliances. For "Class I" during the earth test to prove continuity between earth pin and metal parts on the appliance. For "Class II" during the insulation test to prove the insulation between active-neutral and the metal parts of the appliance. ie there is no leakage from mains coming into the appliance to the metal parts that are exposed.

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