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Digital Volt Meters (DVMís) are categorized depending on the risk and severity of transient over-voltage that might occur at the point of test. Transients are short-lived burst of energy induced in a system, e.g. caused by lightning strike on a power line.

On high-energy circuits this leads to hazardous situations as these circuits might provide enough current to feed an arc-over resulting in a plasma breakdown or even explosion. Higher CAT-identification refers to electrical environments with higher power and possibly higher energy transients.

 

 

CAT I

A CAT I rated meter is suitable for measurements on protected electronic circuits that are not directly connected to mains power. <100V (Battery operated devices, Audio Circuits, Education)

 

CAT II

A CAT II-rated meter is suitable for measurements in CAT I-environments, as well as for measurements in single-phase appliances that are connected to the mains by means of a plug. Measurement of normal domestic circuits, provided that the circuit is at least 10m apart from any CAT III- or 20m apart from any CAT IV-environment. < 240V (Household Appliances, Portable Tools, Sound and Lighting Equipment)

 

CAT III

A CAT III-rated meter is suitable for measurements in CAT I- and CAT II-environments, as well as for measurements on (fixed) single and three phase appliances which are at least 10m apart from of a CAT IV-environment, and for measurements in or on distribution level equipment. <440V (Fuse boxes, Lighting circuits, Ring main, Electric ovens).

 

CAT IV

A CAT IV-rated meter is suitable for measuring in CAT I-, CAT II- and CAT III-environments as well as on the primary supply level. Note that for all measurements on equipment for which the supply cables run outdoors (either overhead or underground) a CAT IV meter must be used.

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ESR Electronic Components Ltd Cullercoats Tyne and Wear NE30 4PQ