Tools, Equipment, Instruments and Testing
Domain 11 - Tools, Equipment, Instruments and Testing. The exam checks that you can select the right instrument, connect it correctly and interpret what it shows.
Common instruments
- Insulation tester (megger): 500 V for LT, 1 kV for LT equipment and 5 kV for 11 kV cables; never on a live circuit, and always discharge the item afterwards.
- Earth tester with three spikes, using the fall-of-potential method; drive stakes in a straight line at adequate spacing and check that readings are stable.
- Clamp meter (tong tester) for load current without breaking the circuit; multimeter for voltage, continuity and resistance; phase sequence tester before paralleling or charging.
- Specialised kits: oil BDV set, transformer ratio tester, contact resistance meter, cable fault locator, HT phasing stick and voltage detector.
Hand tools
Lineman's pliers, screwdrivers, spanners, hacksaw, crimping tool, torque wrench, chain pulley, come-along, safety belt, gang operating stick and discharge rod. Inspect insulated handles before every job and discard cracked tools.
Worked example
A clamp meter reads 60 A, 58 A and 62 A on a 415 V feeder at 0.85 power factor. Using the average 60 A: P = √3 × 415 × 60 × 0.85 = 36.7 kW. Near-equal phase currents mean a balanced load; a persistent difference of more than about 10% points to an unbalanced single-phase load or a CT problem.
Traps
- Using a multimeter to judge insulation resistance.
- Testing a live circuit with a megger, which damages the instrument and endangers the user.
- Driving earth-test spikes too close together or in a loop, giving falsely low readings.
- Trusting an uncalibrated instrument or a test lead with exposed insulation.