Isolation Transformer Test Bench with Leakage Protection for Electronics Labs

An isolation transformer test bench gives an electronics lab a safe way to power and test mains-powered equipment that is under repair, under development, or being demonstrated. In a wall socket, one side of the supply is tied to earth, so touching a part while standing on an earthed floor can complete a circuit through the body, and clipping an oscilloscope ground lead to the wrong point can short the circuit under test. This bench breaks that path. A 1:1 isolation transformer passes 230 V across at the same voltage while its secondary floats free of earth, so there is no return path through the bench earth for a single fault to exploit. The bench adds a leakage-current meter, an MCB, and earth-fault protection that cut the supply when stray current appears, plus shrouded test sockets and indicator lamps that make the bench state visible at a glance. It is a lab tool for supervised testing, not a certified product.

The isolation transformer test bench works end to end as a chain of five stages: mains input, galvanic isolation, floating test socket, continuous measurement, and protection. Mains at 230 V and 50 Hz enters through a fused inlet and the MCB, which guards against overcurrent. It then feeds the primary of a 1:1 isolation transformer, whose secondary delivers the same 230 V but floats free of earth because the two windings share only a magnetic field, not a wire. The floating secondary feeds shrouded test sockets where the equipment under test is plugged in, so a single accidental contact cannot complete a circuit back through earth. While the equipment runs, a leakage-current sensing circuit measures stray current flowing to earth and shows it on a digital panel meter in milliamps, with green and red lamps showing healthy and fault states. If leakage crosses the design trip level, the earth-fault protection trips and disconnects the test socket.

1. Mains at 230 V AC and 50 Hz enters the bench through a fused inlet and the 16 A MCB.
2. The MCB feeds the primary winding of the 1:1 isolation transformer.
3. The floating secondary delivers 230 V AC at 50 Hz to the shrouded LINE and NEUTRAL test sockets, with no earth reference.
4. The equipment under test is plugged into the test sockets and powered from the floating supply.
5. The leakage-current sensing circuit continuously measures stray current to earth and displays it in milliamps on the panel meter.
6. If leakage crosses the 30 mA trip level (design target) or an overcurrent occurs, the protection module and MCB disconnect the test socket and the red lamp shows the fault state.

Builder note: the secondary must stay floating. If the bench earths the secondary neutral — the single most common wiring mistake on the test-socket side — the isolation is gone and the bench behaves like an ordinary wall socket, silently. The build checks this with a continuity test between the secondary and earth before first power-up: it must read open. Galvanic isolation breaks the earth-return path, so an oscilloscope ground clip no longer shorts the circuit under test.

Tech stack:

• 1:1 isolation transformer
• MCB · earth-fault protection
• Leakage-current sensing
• Digital panel meter
• Shrouded test sockets
• Steel enclosure · ventilation
• Mains wiring · earthing practice
• Multimeter · insulation tester (verification)

Four systems in the bench work together: a floating 230 V supply, visible leakage monitoring, fast fault disconnection, and a bench that is safe to operate by hand. The 1:1 isolation transformer is the core, removing the earth reference from the test supply so oscilloscope ground clips and accidental contact no longer create a short or a shock path. A digital panel meter continuously displays leakage current in milliamps, so a developing fault is seen before it becomes dangerous. Earth-fault protection and a 16 A MCB cut the supply when leakage or overcurrent crosses the trip level, and the trip is indicated by a red lamp. Shrouded test sockets, a ventilated steel enclosure, and clear labelling keep live parts out of reach during normal use. Together these make the bench a practical teaching tool for transformer isolation, earthing, and protection.

• [1:1 isolation transformer] A 250 VA (design value) transformer with equal primary and secondary windings delivers 230 V at 50 Hz while keeping the secondary floating, so the test supply has no earth reference.
• [Floating shrouded test sockets] Two shrouded 4 mm sockets (LINE and NEUTRAL) accept the equipment under test, with recessed contacts that keep fingers clear of live metal during normal use.
• [Leakage-current display] A digital panel meter continuously shows leakage current in milliamps, so stray current through a faulty device is visible while the test is running.
• [Earth-fault protection trip] A protection module disconnects the test socket when leakage crosses the 30 mA trip level (design target), with a red lamp showing the tripped state until it is reset.
• [MCB overcurrent protection] A 16 A C-curve MCB (datasheet value) guards the bench and the equipment under test against overload and short circuit on the mains side.
• [Status indicator lamps] Green and red panel lamps show power-on and fault states at a glance, so the bench state is obvious from across the lab bench.
• [Ventilated steel enclosure] A grounded steel enclosure with ventilation slots houses the transformer and wiring, keeping live parts enclosed and heat from building up inside.

Optional customization (not in the base build): data logging of leakage readings to a laptop over USB, for recording fault behaviour during a demonstration.
Future scope (not in the base build): automatic test-sequence logging with a microcontroller, and a remote trip-status indicator for the lab supervisor's desk.

• Working isolation transformer test bench, assembled, wired and tested
• 1:1 isolation transformer, MCB, earth-fault protection module and leakage-current meter fitted in the enclosure
• Wiring diagram and component list with ratings
• Test report covering continuity, isolation and trip checks carried out before dispatch
• Project report PDF (background, transformer theory, protection coordination, methodology, test results)
• PPT presentation for final review
• Viva Q&A preparation document (isolation, earthing, leakage current, protection devices)