Electrical Safety
Scope
The paper tests the Indian Electricity Rules 1956, electric shock physiology, first aid, fire fighting and safe working procedures on LT and HT installations.
Core rules
- IE Rules voltage bands: low voltage up to 250 V, medium 250–650 V, high 650 V–33 kV, extra-high above 33 kV.
- Shock severity depends on current, path and duration. About 1 mA is perceptible, 10–15 mA causes let-go failure, 30 mA can stop breathing, and 50–100 mA through the chest can cause ventricular fibrillation.
- Dry body resistance is roughly 1,000–5,000 Ω; wet skin can fall below 500 Ω, which is why wet-hand contact is far more dangerous.
- Isolate, lock out and tag out before work; prove dead with a tester; discharge capacitors; use rubber gloves and mats for LT work.
- Electrical fires: CO₂ or dry powder, never water or foam. Rescue a victim only after switching off the supply, or use insulated material.
Worked example
A worker with wet hands (500 Ω) touches a 230 V live conductor. Current = 230/500 = 0.46 A = 460 mA - far above the fibrillation threshold, and the contact time would decide survival. With dry hands at 2,000 Ω the current is 115 mA, still dangerous. A 30 mA RCCB would disconnect in under 30 ms and prevent the shock becoming fatal, provided the earth loop is healthy and the device is tested regularly.
Traps that cost marks
Saying voltage kills rather than current; grabbing a shocked person with bare hands; using water on an electrical fire; and assuming rubber gloves replace isolation. Artificial respiration must begin immediately after the supply is cut, without waiting for an ambulance.