HT instruments HT5 - Manual (Page 4)

HT5
EN - 3
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 measurement category,
commonly called overvoltage category. 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 withstanding capability of the equipment is
made known to the user.