HT instruments HT78 - Manual (Page 4)

HT78
EN - 3
1.2. BEFORE USE
Always keep to the instructions contained in this manual:
CAUTION
Non compliance with the warnings and/or the instructions may damage the
tester and/or its components or injure the operator.
• When the clamp is connected to the circuits to be tested, never touch unused terminals
• When measuring current, any strong current near or close to the clamp jaw will affect
the accuracy
• When measuring current, always put the tested conductor in the middle of the clamp
jaw in order to obtain a more accurate reading
• If the reading value or the sign indication remains unchanged during the measurement,
check if the HOLD function is active
1.3. AFTER USE
• Once the measurements are completed, turn OFF the meter
• If you expect not to use the clamp for a long time, remove the batteries
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 § 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.