In which wire, switch should be connected?

Question

Examoogle · Accepted Answer

Phase

Explanation: According to the Indian Electricity (IE) Rules, a switch must always be connected in the phase (live) wire to ensure the equipment is electrically isolated from the supply source when the switch is in the 'OFF' position. If the switch were in the neutral wire, the device would remain live even when turned off, posing a severe shock hazard during maintenance.

Working Principle: Connecting the switch in the phase wire acts as a series disconnect mechanism. When opened, it breaks the path of the flow of electrons from the live supply to the load, resulting in zero potential difference across the appliance terminals. This renders the appliance safe for handling, as no current can flow through it to the ground.

Key Formulas: $V_{terminal} = V_{supply} 	imes (1 - S)$ — where $S=1$ (Open) for switch off state, isolating voltage.; $I = \frac{V_{phase}}{R_{load}}$ — circuit current remains zero when switch is in the phase line.

Key Points: Switching the phase wire provides complete electrical isolation.; IE Rules mandate phase-switching to prevent accidental electrocution.; Neutral wire must remain continuous to provide a return path for current.; Neutral is usually earthed at the transformer end, making it safer than the phase wire.

Advantages: Ensures safety during equipment repair.; Prevents internal components of the load from remaining energized.; Compliant with international and national safety standards.

Disadvantages: Requires proper identification of phase versus neutral before installation.; Incorrect wiring (swapping phase and neutral) can lead to hazardous conditions.

Applications: Domestic wiring circuits.; Industrial control panels.; Safety breakers and MCBs.

Additional Info: Option B (Neutral) is incorrect because cutting the neutral leaves the appliance internally connected to the high-voltage phase, which is a major safety violation.. Option C (Earth) is incorrect as the earth wire is purely for safety (leakage current path) and should never be interrupted by a switch.

Answer: A is correct — The switch must always be connected to the Phase wire to isolate the load from the live supply when the circuit is switched off.

Exam Tip: In competitive exams, always remember: Switch goes in the 'Live/Phase' line, Fuse goes in the 'Live/Phase' line, but a Circuit Breaker or Earth Leakage device monitors both to ensure safety.

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