HT instruments HT9022 - Manual (Page 7)

HT9022
EN - 5
1.4. DEFINITION OF MEASUREMENT (OVERVOLTAGE) CATEGORY
Standard CEI 61010: Safety requirements for electrical equipment for measurement,
control and laboratory use, Part 1: General requirements” defines what measurement
category, commonly called overvoltage category, is. In § 6.7.4: Measured circuits, circuits
are divided into the following measurement categories:
(OMISSIS)
• 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 on installations inside
buildings.
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 standard requires that the transient withstand
capability of the equipment is made known to the user.