The Cable System from Source to Load
A cable is one part of a system that is designed, installed, terminated, tested and maintained as a whole.
12 min
Activities: 0 of 2
A cable is a system, not a product
A buyer orders a drum of cable. An engineer installs a cable system. The system is the cable itself, the glands that hold it, the terminations at each end, the joints along the route, the supports and trays that carry it, the fire stopping where it passes through walls, and the records that say where it all is.
Each part can fail on its own. A perfect cable with a poor termination fails at the termination. A perfect termination on a cable crushed by an overfilled tray fails in the tray. When a circuit trips, the question is never only "is the cable faulty?" but "which part of the system failed, and why?"
This course follows that system through its whole life. It assumes you already know basic electrical principles — Ohm's law, the meaning of phase and neutral, and why protective earthing exists. It builds on that to the level of a technician or engineer who must choose, install, terminate and prove cables without supervision.
The life of a cable circuit
- 1
1
Design
The load, the route and the fault level decide the cable type and size. The result is a cable schedule entry and a datasheet. - 2
2
Procurement and receipt
The drum arrives. Check the marking, length, drum condition and end caps against the order before it goes into store. - 3
3
Installation
The cable is pulled, laid or cleated along the route without exceeding its bending radius or pulling tension. - 4
4
Termination and jointing
Glands, lugs, stress control and earthing are fitted. Most lifetime failures start here. - 5
5
Testing and energisation
Continuity, phasing and insulation tests prove the circuit and give a baseline for the future. - 6
6
Operation and maintenance
Periodic inspection, thermography and trend testing catch decline before it becomes a fault. - 7
7
Fault, repair or replacement
Faults are located, repaired with a joint, retested and recorded.
Why the stages depend on each other
Decisions made early limit what can be done later. Two examples show this.
Example 1 — a pump feeder. A designer sizes a cable for running current only. The installer pulls it correctly, and the jointer terminates it well. At commissioning the motor will not start: the voltage at its terminals collapses during acceleration. No amount of good workmanship can fix a design error. The cable must be replaced or a second one added in parallel.
Example 2 — a substation tray. The design is sound, but during installation the team pulls the cable around a tight corner at half its permitted bending radius. Every test at commissioning passes. Eighteen months later the insulation breaks down at that corner. The test baseline taken at commissioning helps the fault team, but the damage was done on the day of the pull.
A competent person therefore looks both ways: back at the decisions that limit their work, and forward at the people who will depend on it.
The parts of a cable system
Match the problem to the stage where it started
Each failure below began at one stage of the cable's life. Match them.
- Motor fails to start because of voltage drop
- Insulation fails at a tight bend after a year
- Hot spot found at a lug by thermography
- Fault team digs in the wrong place
A new feeder trips on its first start. Every test at commissioning passed. Which question should come first?