Trade Test for Grade A Electrical Work
Trade Test for Grade A Electrical Work
This domain is the practical trade test for Grade A electrical work in Hong Kong. It assesses whether you can install, terminate, inspect and test a low-voltage final circuit to the standard expected of a registered electrical worker, within the Grade A scope set by the Electricity (Registration) Regulations. Marking is usually weighted across safety, dimensional accuracy, workmanship, testing and completion.
Core rules and concepts
- Know your grade limit. Grade A work is restricted to low-voltage installations up to the maximum demand set for that grade. Do not accept or certify work beyond your registration.
- Work to the drawing and the Code of Practice. Dimensions, heights, conduit runs, accessory positions and cable routes are marked. The Code of Practice for the Electricity (Wiring) Regulations is the reference for selection, erection, inspection and testing.
- Terminations must be mechanically and electrically sound. Strip to the terminal length, avoid nicked strands, insert fully, tighten to the manufacturer’s torque, and ensure the sheath enters the enclosure.
- Protective devices and earthing must match the circuit. MCB rating, RCD type and rating, CPC size and polarity are checked before energising.
- Test sequence: visual inspection, continuity, insulation resistance, polarity, earth fault loop impedance, RCD operation and functional test; record every result.
Worked example
A 20 A radial socket circuit is wired in 2.5 mm² twin and earth, 15 m long, with a 20 A Type B MCB and a 30 mA RCD. Results: insulation resistance L-N 200 MΩ, L-E 200 MΩ, N-E 200 MΩ; CPC continuity 0.18 Ω; polarity correct; loop impedance 0.85 Ω; RCD trip time 24 ms at 1×IΔn. Is it acceptable?
Reasoning: insulation resistance is well above the 1 MΩ minimum; CPC continuity is low, confirming the protective conductor; polarity is correct. The loop impedance must be compared with the maximum permitted for the 20 A Type B device for the required disconnection time; 0.85 Ω may be acceptable but must be checked against the Code of Practice or manufacturer table, not guessed. The RCD trips within 300 ms at 1×IΔn. Record all values and complete the test certificate before handover.
Traps that cost marks
- Reversed polarity at a socket or switch.
- Sheath cut back too far, exposing live conductors.
- Over-tightened or loose terminals.
- Testing with loads or sensitive equipment connected.
- No test record or incomplete schedule.
- Poor housekeeping and unsafe tool use.