Within the United Kingdom there is a requirement that all appliances that are used within a place of work must be tested and confirmed as being safe to use. While there is no law that specifies the minimum date between tests on appliances, the Insitute of Electrical Engineers and the Health and Safety Executive recommend the following:
High powered contruction equipment – Every 3 months
Office equipment – Maximum of 4 years between tests.
However you must take account of the environment in which the appliances are being used together with the frequency of use. If you have not ensured the equipment that is used by your staff is safe, you may be liable for damages in the event of an accident.
You should ensure that employees within your company are encouraged to report any damages and hazards that they become aware of. This will ensure that problems are rectified before they become an issue.