Adding a geyser and AC to a 1.5 mm² socket circuit in a tailoring unit
A small tailoring unit in a Haryana village has a single-phase 230 V supply protected by a 32 A MCB. The existing wiring is 1.5 mm² copper PVC cable in buried conduit feeding three 6 A sockets through a chain of looped joints, and two junction boxes were plastered over during a recent wall repair. The owner now wants to add a 2 kW geyser and a 1.5 kW air conditioner on the same final circuit, and reports that the lights dim noticeably when the sewing machine starts. The distance from the distribution board to the far socket is about 22 m. The local electrician proposes simply replacing the 32 A MCB with a 40 A one 'so it will not trip', and joining the new geyser point to the nearest existing socket.
1. Calculate the current the two new appliances would draw on the existing circuit and evaluate the 40 A MCB proposal.
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Combined new load = 2000 W + 1500 W = 3500 W. At 230 V, I = 3500 / 230 ≈ 15.2 A, and that is before the sewing machine and the existing socket loads are counted. A 1.5 mm² copper PVC cable in conduit is typically rated around 10–14 A, so the new load alone exceeds the cable's capacity.
The 40 A MCB proposal is unsafe. An MCB exists to protect the cable, not to stop nuisance tripping. A 40 A device will carry roughly three times the cable rating before it even begins to operate thermally, so the cable will run hot, the PVC will soften and crack, joints will carbonise, and a fire can start inside the conduit before the MCB ever sees a fault. The correct sequence is: calculate the load, select the cable for that load and for voltage drop, then select a protective device whose rating does not exceed the cable's current-carrying capacity.
2. Explain the dimming lights and why the plastered-over junction boxes and looped joints are a serious defect.
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Dimming: the sewing machine draws a starting current several times its running current for a fraction of a second. That surge across the resistance of a long 1.5 mm² run plus loose, oxidised joints produces a voltage dip at the lamps. Quick estimate for the run: 44 m of copper at 1.5 mm² gives R ≈ 0.0175 × 44 / 1.5 ≈ 0.51 Ω; at 15.2 A the drop is about 7.8 V, roughly 3.4% - already at the usual final-circuit limit, and worse at motor start. On 2.5 mm² the same calculation gives about 4.7 V (about 2%), which is acceptable.
Buried joints: a joint is the weakest point in a circuit. Plastering it into the wall makes it inaccessible, traps moisture, and hides the heat and arcing that a loose screw or twisted joint produces. Standards require joints to be made only in accessible junction boxes using proper connectors. Looped joints in a chain also mean every downstream socket depends on the upstream connections, so one loose terminal can kill or overheat several points. The wall should be opened, the joints re-made in accessible boxes, and the circuit split.
3. Recommend a compliant arrangement for the geyser and AC, including cable sizes, device ratings and the checks you would make before energising.
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- Separate dedicated circuits. Geyser: 2000 W / 230 V ≈ 8.7 A, so a 2.5 mm² circuit with a 16 A MCB. AC: 1500 W / 230 V ≈ 6.5 A, so its own 2.5 mm² circuit with a 16 A MCB. Keep the lighting and general sockets on their own 1.5 mm² circuits with 6 A or 10 A devices.
- Protect people, not just cable. Provide a 30 mA RCCB for the socket and wet-area circuits, and verify it trips on test.
- Match the existing board to reality. Replace the 32 A MCB with devices that actually protect the smaller cables; a 32 A device on 1.5 mm² is already wrong.
- Earthing: verify the earth continuity to every socket and to the geyser body before commissioning.
- Before energising: insulation resistance test (at least 1 MΩ), polarity check, tightness of terminals, and a load test to confirm the voltage at the far socket stays within about 3% of supply with the geyser on.