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EN - 6
1.4. MEASUREMENT CATEGORIES - DEFINITIONS
The IEC/EN61010-1 guideline (Safety requirements for electrical equipment for
measurement, control and laboratory use, Part 1: General requirements) defines
what a measurement category (usually called as Overvoltage Category) is. At §
6.7.4: Measuring circuits it says:
Circuits are divided into the following measurement categories:
x Measurement category IV is for measurements performed at the source of the
low-voltage installation.
Examples are electricity meters and measurements on primary overcurrent
protection devices and ripple control units.
x Measurement category III is for measurements performed in the building
installation.
Examples are measurements on distribution boards, circuit breakers, wiring,
including cables, bus-bars, junction boxes, switches, socket-outlets in the fixed
installation, and equipment for industrial use and some other equipment, for
example, stationary motors with permanent connection to fixed installation.
x Measurement category II is for measurements performed on circuits directly
connected to the low voltage installation.
Examples are measurements on household appliances, portable tools and similar
equipment.
x Measurement category I is for measurements performed on circuits not directly
connected to MAINS.
Examples are measurements on circuits not derived from MAINS, and specially
protected (internal) MAINS-derived circuits. In the latter case, transient stresses
are variable; for that reason, the norm requires that the transient withstand
capability of the equipment is made known to the user.
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