Estimation, Testing and Measuring Instruments
What this domain tests
Estimation, Testing and Measuring Instruments tests load estimation, bill of quantities, cable and protective-device selection, and correct use of megger, multimeter, clamp meter, earth tester and phase sequence indicator.
Core rules
- Estimation starts with connected load, demand factor and diversity; then size cables for current, voltage drop and short-circuit withstand.
- A BOQ lists items, sizes, quantities and units; add wastage only where the schedule permits.
- A megger measures insulation resistance, not continuity. A multimeter measures voltage, resistance and continuity on dead circuits. A clamp meter measures current without breaking the circuit.
- Earth testers use a known electrode arrangement; phase sequence indicators check rotation direction.
Worked example
A 25 m single-phase run carries 16 A. The cable table gives 9 mV/A/m. Voltage drop = 9 × 16 × 25 / 1000 = 3.6 V. On 230 V this is 1.6%, within a typical 3% limit. The same cable must also have a current rating above 16 A after derating, and the protective device must protect the cable.
Traps that cost marks
Measuring resistance on a live circuit, using a megger on electronic equipment without disconnection, reading a clamp meter around both live and neutral together, and estimating cable size from load current alone. Record instrument range, zero and calibration status.