HT instruments HT21 - Manual (Page 4)

HT21
EN - 3
1.2. DURING USE
Read the recommendations which follow and the instructions in this manual:
CAUTION
An improper use may damage the instrument and/or its components or injure
the operator.
 When changing the range, first disconnect the test leads from the circuit under test in
order to avoid any accident
 When the instrument is connected to measuring circuits never touch any unused
terminal
 When measuring resistors do not add any voltage. Although there is a protection
circuit, excessive voltage could cause malfunctioning
 If during measurement the displayed values remain constant check whether the HOLD
function is active
1.3. AFTER USE
 After using the instrument turn it off
 If you expect not to use the instrument for a long period remove the battery to avoid
leakages of battery liquids which may damage its inner components
1.4. MEASURING (OVERVOLTAGE) CATEGORIES DEFINITIONS
EN 61010-1: Safety requirements for electrical equipment for measurement, control and
laboratory use, Part 1: General requirements, gives a definition of measuring category,
usually called overvoltage category. § 6.7.4: Measuring circuits:
(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