School of Life Hacks
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    Gloved hands reaching into the opened rear panel of an appliance, a row of screwdrivers laid out on a folded towel, a green work light overhead.

    The Electricity You Can Measure Safely

    Enough electrical theory to take a reading that means something, and enough discipline to never take one you should not.

    Module 2 of 74 lessonsWritten in full1 worksheet
    Start this moduleThe whole course

    The lessons

    All 4, in the order they are read.

    1. 1. Volts, amps and ohms, in practice
      Three quantities, three questions, and the one you can measure without energising anything.
    2. 2. Continuity, and proving a circuit dead
      Lock out, test the tester, test the circuit, test the tester again. The sequence is not optional.
    3. 3. Switches, thermostats and sensors
      Most household 'electronics' faults are a mechanical switch that no longer closes or a thermistor that has drifted.
    4. 4. Motors and what actually kills them
      Bearings, capacitors and windings fail in distinguishable ways, and two of the three are cheap.

    The worksheet

    Safe-measurement checklist and reading sheet

    The top block is a checklist you complete every single time before a probe touches anything. The bottom block records the readings. A sheet with readings and an incomplete checklist is a sheet you throw away.

    Safe-measurement checklist and reading sheet
    StepDoneNote
    Appliance unplugged, or breaker off AND locked/tagged——
    Tester proved on a known live source——
    Circuit tested — confirmed dead——
    Tester proved again on the known live source——
    Capacitors discharged (if the machine has any)—Motor-run and motor-start capacitors hold a charge after power is removed
    Photographs taken of every connector before disturbing it——

    4 further rows in the downloadable sheet.