Electrical Fundamentals and Power Systems
What the exam tests
This domain checks safe low-voltage electrical reasoning for equipment technicians working on Moroccan industrial and building systems: 230/400 V 50 Hz supplies, three-phase motors, protective devices, earthing, and power quality. Questions often ask you to select a device, interpret a measurement, or explain why a protection operates.
Core rules
- Use Ohm's law and AC impedance; for three-phase active power P = √3 × U × I × cos φ. Motor input power is shaft output divided by efficiency.
- In Morocco the declared LV supply is 230 V phase-to-neutral and 400 V phase-to-phase, 50 Hz; verify at the terminal rather than assume.
- Earthing system changes fault behaviour: TT relies on RCDs and local earth electrodes; TN relies on protective conductors and automatic disconnection.
- An RCD detects earth leakage; it does not replace overload or short-circuit protection. Discrimination prevents an upstream device tripping before the faulty final circuit.
- The neutral is a live conductor in operation; never switch or fuse it alone unless the design requires simultaneous isolation.
Worked example
A 7.5 kW, 400 V, three-phase motor has efficiency 0.89 and power factor 0.82. Input current I = 7500 / (√3 × 400 × 0.82 × 0.89) = 14.8 A. A thermal overload set at 1.05 × full-load current is about 15.5 A; confirm cable ampacity, ambient derating, and starting method before final setting. Do not set the overload to the motor nameplate current if the nameplate gives shaft output only.
Traps
Using 230 V in the three-phase formula; ignoring efficiency and power factor; treating an RCD as motor overload protection; assuming a tripped breaker is the fault; and measuring phase current without checking imbalance.