Multimeter simulator

You learn to use a multimeter by measuring, but mistakes on live circuits are expensive. In this simulator you can measure on a three-phase supply and on a 24 V control circuit, make the classic mistakes with no risk, and track down faults. Choose a function on the selector, place the red and black probes on two terminals and look at the display: underneath, each reading is explained.

Circuit

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Selector

Red lead jack

The circuit

Place:

Find the fault

A random fault is enabled without telling you which one. Find it by measuring only.

Try this

How to use it

Selector: AC volts, DC volts, ohms, continuity or amps, as on a real meter.
Red lead jack: for voltage, resistance and continuity it goes in the V Ω jack; to measure current it has to move to the A jack. When you change jacks the probes come off the circuit, as they would in real life. Forgetting to move it back to V Ω is one of the most common accidents.
Probes: choose the red or the black probe and touch a terminal on the diagram or in the list. After you place one, the other is selected.
The circuit: open or close the isolator, switch the supply off, press the stop button or enable faults and see how the readings change.

What each circuit teaches

Three-phase supply: why there are 230 V between phase and neutral and 400 V between phases, what to expect between neutral and earth, how to prove dead, and how the wrong range can fool you.
24 V control circuit: how to find a fault by measuring point by point to 0 V, why an open component has the full voltage across it, how to check a coil and how to measure current in series.

Mistakes that cost nothing here

Measuring on amps across two live points: it is a short circuit through the meter.
Leaving the red lead in the A jack and then measuring voltage.
Measuring resistance or continuity on a live circuit.
Measuring the mains on the DC range and thinking it is dead.
Trusting the reading on a floating point that is not connected to anything.

Real voltages and wire colours

The supply in the simulator is 230/400 V at 50 Hz with IEC wire colours (brown, black and grey phases, blue neutral, green-yellow earth), as used in the UK, Europe and much of the world. In North America the voltages (for example 120/240 V or 277/480 V at 60 Hz) and the colours are different, but the measuring technique and the mistakes are exactly the same.

A simulator is not an installationThe values are those of an ideal case: every real meter has its own continuity threshold, input impedance and way of reacting to mistakes. For real work, use a meter with the right category rating (CAT III or CAT IV in panels), leads in good condition, and prove dead with a voltage tester following a safe isolation procedure.

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