Electrical Systems and Power Distribution
Core concepts
Understand single- and three-phase power, voltage, current, resistance, and power factor. Know Ohm's law, W = V·I, and the three-phase power formula P = √3·V·I·PF. Familiarize yourself with motors (induction, synchronous), starters, contactors, overloads, and motor protection. Understand transformers, switchgear, breakers, and grounding. Know the difference between kW and kVA and why power factor matters. Recognize electrical hazards: arc flash, lockout/tagout, and PPE requirements.
Traps to watch
- Forgetting √3 in three-phase power calculations.
- Confusing kW (real power) with kVA (apparent power).
- Assuming a motor draws nameplate current - actual draw depends on load.
- Overlooking power factor correction when sizing feeders.
- Ignoring lockout/tagout before working on energized equipment.
Worked example / rule of thumb
A 480 V, three-phase motor draws 50 A at 0.85 PF. P = √3 × 480 × 50 × 0.85 ≈ 35.3 kW. Rule of thumb: √3 × 480 ≈ 831, so P ≈ 831 × I × PF - handy for quick estimates.