Jointing, Termination and Service Connection Work
This domain covers making reliable electrical connections: overhead conductor joints and taps, cable joints and terminations, and the consumer service connection. The exam tests joint selection, cable preparation, termination procedure, service cable sizing and the reasons joints fail.
Core rules
- Overhead joints and taps use compression clamps, mechanical connectors or automatic connectors rated for the conductor material and size. Aluminium-to-copper connections need a bimetallic interface to prevent galvanic corrosion.
- Cable joints must restore insulation, stress control, moisture sealing and mechanical protection. Heat-shrink or taped joints are used according to cable type and voltage; joints in underground cable should be in a joint bay or box.
- Terminations need correct cable gland, lug, sealing and phase identification. Stress cones or stress-control tape are used on HT cables.
- A service connection runs from the distributor to the consumer's meter board. It includes service cable, fuse or MCB, meter, main switch and earthing. The service cable must carry the consumer's load with acceptable voltage drop.
Worked example
A single-phase consumer has a 5 kW load at 240 V and a 30 m service run. Select a copper conductor and check voltage drop.
Current = 5000/240 = 20.8 A. Try 4 mm² copper. Using resistivity 0.0175 Ω·mm²/m and a single-phase loop length of 2 × 30 m: V_drop = 2 × I × ρ × L / A = 2 × 20.8 × 0.0175 × 30 / 4 = 21.84 / 4 = 5.46 V. That is 5.46/240 × 100 = 2.3%, within a typical 5% limit. The 4 mm² cable also has a current rating above 20.8 A. A 2.5 mm² cable would give 8.74 V drop (3.6%) and less current margin, so 4 mm² is the better choice.
Traps that cost marks
- Using a connector not rated for the conductor material or size.
- Joining aluminium to copper without a bimetallic connector.
- Forgetting the return path in single-phase voltage-drop calculations.
- Poor termination causing a hot joint, Tracking or failure.
- Not sealing cable ends against moisture.