Records of maintenance, including (but not limited to) inspections and tests, should be kept throughout the working life of the electrical equipment.
Such records are a useful management tool for reviewing the frequency of the inspection and testing, and ensuring that regular inspection has been carried out.
The Standard AS/NZS 3760 recommends that inspection and testing records be retained for a period
not less than seven years.
source - "WorkCover - Frequuently Asked Questions - Testing and Tagging of Electrical Equipment"