Guide to Overvoltage Categories and Measurement Categories
07 September 2022
The GAMBICA Guide to Overvoltage Categories and Measurement Categories explains clearly and simply the meaning and significance of the different measurement and overvoltage categories specified in British Standards and the Health & Safety Executive’s guidance GS38.
THE GAMBICA Test and Measurement sector has produced independent guidance to help electricians better understand measurement categories ratings for testing equipment, and where the boundaries lie within an electrical installation. The guidance was deemed necessary because so many professional electricians are having to go back to equipment providers to check exactly which test equipment is appropriate for which jobs.
The GAMBICA Guide to Overvoltage Categories and Measurement Categories explains clearly and simply the meaning and significance of the different measurement and overvoltage categories specified in British Standards and the Health & Safety Executive’s guidance GS38.
Measurement categories classify the terminals of test and measurement equipment according to the type of mains circuit to which they can be safely connected. The category takes into account overvoltage categories, short-circuit current levels, the location where the test is to be made, and some forms of protection included in the building installation.
It is hugely important that an instrument with an appropriate measurement category and voltage rating is used.
Measurement terminals can be safely connected to a measurement category lower than the marking on the terminals, but the measurement terminals must never be connected to a circuit that exceeds the rated voltage or measurement category.
Measurement categories go from Cat II to Cat IV and the new GAMBICA guidance gives you an idea of where they can be used.
The guidance also explains the transient overvoltages which can occur within electrical distribution systems. They can be caused by atmospheric issues such as a lightning strike or be generated by equipment within an installation. Power electronic modules in particular, generate temporary voltage peaks in conjunction with inductive loads, which can be significantly higher than the nominal mains voltage. Overvoltage categories and measurement categories are used to classify equipment according to its ability to withstand transient overvoltages.