Inside the electrical tester's toolkit

Accurate troubleshooting relies on using the proper tool for the job.

By Benjamin D. Miller, P.E.

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Keeping the facility’s power system operating safely and reliably requires a variety of electrical tests. Do you have the right tools for the job? Here’s a rundown of some of the more common equipment that you might need.

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Figure 1. The hand-held digital multimeter is the workhorse of the circuit testing tools available.
Figure 1. The hand-held digital multimeter is the workhorse of the circuit testing tools available.

Digital multimeter

Digital multimeters (Figure 1) are the most common type of electrical test equipment and are the workhorses for electrical testing. Applications for multimeters are numerous and include testing voltages at both power and control levels, measuring the current to various loads, checking the resistance of motor and transformer windings and other components, and testing continuity of relay or switch contacts and wiring.

Almost every multimeter measures AC and DC voltage and current, and resistance. Voltage measurements generally range from millivolts to 1,000 volts. Current ranges generally run from milliamps to as much as 10 amps. Resistance measurements typically are from less than one ohm to tens of megohms. Many models have additional functions such as continuity buzzers, temperature, capacitance, frequency and diode testing. More advanced models include peak hold, inrush current, max/min recording, data logging and PC communication for setup and data storage.

Meters that measure true RMS (TRMS) values are more accurate than average-responding meters when waveforms contain harmonics, such as the voltages and currents in motor drives and power supplies.

Non-contact voltage detector

Figure 2. The non-contact tester indicates whether a circuit or component is deenergized.
Figure 2. The non-contact tester indicates whether a circuit or component is deenergized.

These instruments are simple and effective for quickly determining whether voltage is present on a circuit or in a panel (Figure 2). However, you must verify that they’re working properly if you want to rely on them for confirming voltage absence (see sidebar, “Safety takes three steps”). A follow-up test with a multimeter is recommended to confirm that conductors are deenergized before performing work on the circuit. Various models use lights, buzzers or both as the indicating signal.

Solenoid voltage detector (Wiggy)

These instruments have been around for many years and are still popular with many electricians. The original design uses a solenoid to move a pointer, which indicates the nominal system voltage level. They don’t give precise readings of actual voltage. In addition to the pointer, solenoid vibration provides an audible indication of voltage presence. They require no batteries and are rugged enough to bounce around in a tool box without damage.

Hi-pots don’t measure insulation resistance. They measure the resulting leakage current and sense the presence of breakdown.

– Benjamin D. Miller, P.E.

Now for the bad news. While many of these units are still in service, they don’t comply with contemporary test equipment safety standards. Also, the solenoids consume significant power from the circuit under test and produce a voltage transient when making and breaking the connection. As a result, they can damage any sensitive solid-state devices on the circuit. They also can overheat if energized for longer than the recommended duty cycle marked on the instrument, and they are subject to mechanical wear that might render them inaccurate. I don’t recommend using them.

Newer designs mimic the original style instrument, but use indicator lights rather than the solenoid. Some of them actually include a vibrator to provide the feedback of the solenoid. These instruments have acceptable safety ratings and do not cause damage to the circuit under test.

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