prevention of electrical hazards
1. What Electrical Hazards Are
Electrical hazards = potentially harmful events due to electricity: electric shock (current through body), electrical fire (overheating/short), arc flash (plasma explosion), electrocution (fatal), equipment damage.
Prevention = eliminating or controlling conditions that cause hazards via design, protection, and practices.
2. Causes of Hazards (exam list)
| Cause | Hazard |
|---|---|
| Exposed live parts, damaged insulation | Shock |
| Overloading, short circuit | Overcurrent ⇒ heating ⇒ fire |
| Wet/moisture, poor earthing | Low , no fault path ⇒ shock |
| No fuse/MCB, oversized fuse | No protection ⇒ fire |
| Improper earthing | Metal body becomes live on fault ⇒ shock |
3. Prevention Measures (exam list — 7)
| Prevention | How |
|---|---|
| 1. Proper insulation | Use double insulation, no exposed joints, heat-shrink, enclosure IP rating |
| 2. Correct fuse/MCB/MCCB selection | Rated slightly above load (e.g., 5A load ⇒ 6A fuse), fast for semiconductor, slow for motor (inrush) |
| 3. Effective earthing (next topic) | Low path to ground for fault current ⇒ fuse blows quickly |
| 4. Use of ELCB/RCCB (30mA) | Detects leakage (difference between Line and Neutral ) and trips in 30ms ⇒ prevents lethal shock even if earthing fails |
| 5. Safe design: isolation, double insulation | Transformer isolation, SELV (<50V) for wet areas |
| 6. Regular inspection and maintenance | Megger test insulation ( >1MΩ), thermography for hot spots, tighten terminals |
| 7. Safe practices (previous topic) | LOTO, PPE, dry, one-hand |
4. Worked Prevention
Need to prevent fire in home: Install MCB 6A for lighting (1.5mm² wire rated 16A), ELCB 30mA for shock, earthing <5Ω, no extension overload.
Need to protect motor 5HP: MCCB with thermal overload, proper earthing, regular insulation check.
Wet bathroom: Use SELV 12V via isolating transformer + IP65 enclosure.
5. Exam Points
- List causes (exposed live, overload, wet, no protection, poor earthing) — 3-5 marks, frequent.
- List prevention (insulation, correct fuse/MCB, earthing, ELCB, double insulation, inspection) — 5-7 marks, very frequent (the most common hazards prevention question).
- Mention ELCB/RCCB 30mA trip — 5 marks, frequent.
- Show fuse rating slightly above load — 3 marks.