Posted By Alec Wood
Multi-meters which are for general usage, such as the digital hand-helds most electricians keep in their boxes, do not require any calibration since they are used for indication only. The general accuracy of the instrument is sufficient for their purposes. If a phase conductor read 232V and was really at 222V they wouldn't even notice - it's still "live" which is what they are testing for in most instances. Such equipment should be labelled "For reference only" to distinguish it from calibrated equipment.

For the purposes of safety testing though, it is a case of "How do you know the test results are valid?" The answer is usually the equipment is within calibration. If it is not then the only truthful answer would be "We don't!". Typically RCD testers, PAT testers, insulation resistance and earth bonding testers all require calibration. Notice that these are all specific single purpose instruments.

Calibration intervals are generally specified by the manufacturer. The requirements, if any, for equipment calibration can be found in the appropriate regulation. Not that some standards may require the calibration facility itself to have been approved by a notified body.

The short answer is, it depends on what you are testing, but those used for general day to day use do not require calibration.

Alec Wood
Samsung Electronics

Posted By Alec Wood
Also the Institute of Electrical Engineers

www.iee.org

On their site you will find info on 16th edition wiring regs etc