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How often do you check your test leads?

  1. SecondGen's Avatar
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    Jan 2014
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    How often do you check your test leads?

    Test leads are probably the most commonly abused item among test technicians in the field. They get thrown around, stepped on, and fished through apparatus; all of which puts them at risk for damage like nicks and cuts.

    This is why it's important to check your test leads to ensure your test equipment is measuring properly. You wouldn't trust a proximity tester without testing it against a voltage source, would you? In a similar sense, inadequate test leads will result in erroneous results and even potentially pose a great safety risk.

    The best example for testing your leads comes from the Megohmetter. Most handheld testers will go to full scale when testing apparatus with little capacitance, such as a small panelboard. The panelboard may be shorted, however, yet you wouldn't know if your Megger lead developed a break in it the day before.

    A simple way to make sure your handheld Megger is operating properly is to simply tie the two test leads together and try to bring up voltage. If you get a dead short, things are go to go. Performing this test when using first your tester at the beginning of the day is usually adequate, but you should always verify your leads if they accidently get stepped on, or snagged on a sharp object.

    This also seems like a good time to mention a quick visual inspection and cleaning is never a bad idea. It usually only takes a minute at the beginning of the day, just give them a good look over and wipe them down with a dielectric cleaner, such as volts II.

    Here are some different examples of quick ways to calibrate your test equipment in the field:

    Megger - Connect positive (+) and negative (-) leads together and try to raise voltage. Instrument should read zero Megohms and should not produce voltage.

    Multi-meter - Measure voltage against a known source before taking readings. Likewise for resistance. When checking continuity, hold your leads together and verify a low resistance value or audible tone. Never check resistance on a live circuit.

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    Hipot - Simply short the high voltage lead to ground/return and try to bring up voltage. The leakage current should rise sharply and trip the test set.

    Current box / ammeter - use a multi-meter with current clamp and apply a known current, the meter reading on the test set should match the reading from the multi-meter.

    DLRO and ground resistance testers - use resistors (like you would get from radio shack) to calibrate in the field. If you had a 5 ohm resistor, for example, you would put it across C1/P1 and C2/P2 and measure 5 ohms on the display.

    TTR (hand crank) - follow the procedure found in the test set instruction manual on way to perform a field calibration. There are self tests to be performed: null check, zero ratio check, and unity ratio check.

    What are some other ways to field calibrate electrical test equipment? Feel free to contribute by leaving a reply.

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    Jan 2017
    Live dead Live always, test against a known working source first to ensure you device is working properly


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