COMPETENCY 5
MEASURE WITH AN AMPROBE AND AN INSULATION RESISTANCE TESTER
5.1 State the use of an amprobe.
It is used to measure AC or DC current 1
ampere and above.
It does not require the breaking of the
circuit for its connection as for a
conventional ammeter.
Note: Amprobe is a trademark. Other
common names include:- Clamp meter,
Clamp-on meter, Clip-on meter and Tong
tester
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5.2 State the meaning of the term “insulation resistance” and state its units.
This means the resistance of the insulation found on a conductor . The measurement of insulation
being taken between the conductor and its surrounding insulator.
Insulation resistance is measured in Mega Ohms or Megohms (M).
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5.3 List and identify the different parts of an insulation resistance tester.
Hand-Operated or Hand Cranked IRT
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Analog IRT – Battery operated
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Digital IRT
5.4 State the applications of an insulation resistance tester.
(i) It can be used to measure insulation of electrical cables and power lines in M. (HIGH – R)
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(ii) It can be used to check the condition of electric motors, generator windings and power
transformers in M.
(iii) It can be used to measure or to check continuity of a circuit in ohms. (LOW – R)
Note: Insulation of cables/motors/windings can deteriorate due to a number of factors such as
aging, excessive heat or cold, moistures, dirt, corrosive vapours, oil and vibration and it strongly
recommended that IR Test be carried out prevent electrical shocks, assure safety of personnel
and reduce downtime. In addition, a low insulation resistance will lead to leakage currents and
hence a waste of energy and higher running costs.
5.5 State the precautions to be observed.
IRT
(i) IR test shall always be carried out with the power supply disconnected/switched off.
(ii) Remove or disconnect all electronic devices/components, capacitors and neons/lamps
from the circuit before an IRT.
(iii) Check the condition of the meter and test leads before any measurement. Never use
damaged instrument or damaged test leads.
(iv) Never touch the metallic parts of the test probes or metal frames of
machines/equipment during an IRT. Wear insulated electrician’s gloves.
(v) The leads shall be securely in place before any measurement.
(vi) The instrument shall be set on the proper voltage level.
Clamp meters
Note: This instrument is used under live conditions, extra precautions shall be taken.
(i)
(ii)
(iii)
(iv)
(v)
(vi)
Wear insulated electrician gloves.
Damaged instrument shall not be used.
Transformer jaws shall never be touched during measurements.
Ensure that the transformers jaws close completely.
Measurement shall always be taken on one conductor at a time.
Beware of loose cable connections.
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