Electrical Safety and What To Do If Someone Is Shocked

Read this before your first lab session. It is the first experiment in the official list, and it is the only topic in the semester where getting it wrong can injure you.

Why mains electricity is dangerous

It is current through the body, not voltage, that harms — but at 230 V the body's resistance is low enough for a dangerous current to flow.

The "cannot let go" threshold is the one that matters. At around 15 mA the hand grips involuntarily and the victim cannot release the conductor. This is why you never grab a shocked person: they are stuck, and you will be too.

Dry skin resistance is roughly 100 kΩ, but wet skin can fall to about 1 kΩ. At 230 V that is 230 mA — far above the fatal threshold. Wet hands, sweat and damp floors are what turn a survivable contact into a fatal one.

Before you touch anything

1. Switch off at the main and confirm it is off with a tester. A switch in the "off" position is not proof; test.
2. Check the tester works on a known live point first. A faulty tester reads "dead" on everything.
3. Dry hands, dry footwear, dry floor. Wear shoes, not slippers.
4. Remove watch, rings and metal bracelets. A ring shorting across a terminal causes severe burns.
5. Use insulated tools with undamaged handles.
6. Work with one hand where possible, keeping the other away. This keeps any current path away from crossing the chest.
7. Never work alone on a live installation.
8. Know where the main switch is before you start, not after something goes wrong.

The protective devices, and what each actually protects

This distinction is the single most examined point in the workshop viva, and it is genuinely important.

Fuse — a thin wire that melts on overcurrent. Cheap, slow, must be replaced. Protects the cable from overheating.

MCB — Miniature Circuit Breaker. Trips on overcurrent, either thermally (sustained overload) or magnetically (short circuit). Resettable. Also protects the cable, not you.

ELCB / RCCB — Earth Leakage or Residual Current Circuit Breaker. Compares the current flowing out in the live with the current returning in the neutral. If they differ by more than about 30 mA, some current is leaking to earth — possibly through a person — and it trips in about 30 milliseconds.

MCCB — Moulded Case Circuit Breaker. A larger, adjustable breaker for higher currents.

State it plainly: the MCB protects the wiring; the ELCB protects you. An MCB rated at 6 A will not trip at the 50 mA that stops a heart, because 50 mA is nowhere near an overload. Only a residual current device detects that. An installation with MCBs but no ELCB is protected against fire, not against electrocution.

Earthing gives fault current a low-resistance path to earth so that protective devices operate and so that exposed metal never rises to a dangerous voltage. Types you will meet: pipe earthing, plate earthing, and mat/grid schemes; GEM (ground enhancing material) is a backfill that lowers earth resistance in poor soil.

Wiring colours

Indian practice, current standard:

• Brown — live (phase). Older installations: red.
• Blue — neutral. Older: black.
• Green / green-yellow — earth.

Do not assume the colours are correct in an old installation. Test. Miswiring is common, and a reversed live and neutral leaves a switched appliance live at its body even when switched off.

If someone receives a shock

Do not touch the victim. They may still be in contact with the supply, and you will complete the circuit and become a second casualty.

1. SWITCH OFF at the main switch, the MCB or by pulling the plug. This is always the fastest correct action.
2. If you cannot switch off, separate the victim from the supply using dry insulating material — a dry wooden stick, a dry rope, a rubber mat, thick dry cloth. Stand on something dry and insulating. Never use anything metal or damp.
3. Call for help — a teacher, technician, and emergency services. In India, 108 for ambulance.
4. Check response and breathing. Follow ABC: Airway, Breathing, Circulation.
5. If not breathing normally, begin CPR — chest compressions at 100–120 per minute, about 5 cm deep, and continue until help arrives.
6. Treat burns by cooling with clean running water. Electrical burns often have an entry and an exit wound; look for both.
7. Every shock victim must be seen by a doctor, even if they feel fine. Electric current can disturb heart rhythm hours later.

The CPR and first-aid procedures are covered more fully in Health and Wellness (UCPWT127) Module 4.

Fire

For an electrical fire: switch off first, then use a CO₂ or dry powder extinguisher. Never water on live equipment — water conducts, and you will be holding a hose connected to a live circuit.