HT4010
EN - 4
1.4 MEASURING
(OVERVOLTAGE) CATEGORIES DEFINITIONS
The norm IEC/EN61010-1: Safety requirements for electrical equipment for measurement,
control and laboratory use, Part 1: General requirements, defines what measuring
category, usually called overvoltage category, is. On paragraph 6.7.4: Measuring circuits, it
says:
(OMISSIS)
circuits are divided into the following measurement categories:
•
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
•
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
•
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
•
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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