Included in this category are clamp-on, digital, and multimeters; resistance testers; infrared scanners; portable test equipment such as high potential testers; and bench equipment.

The prime function of instruments and test equipment is to help installation and maintenance personnel ensure dependability, efficiency, and profitability of electrical systems and equipment. They are the tools that allow measurements, rather than visual inspections, to determine the status of electrical components and systems. The equipment in this category can range from simple handheld items to precise laboratory instruments. All, however, require a degree of skill to be used properly and to accurately analyze the results.

Handheld meters

The most widely used instruments are the handheld type, which normally includes clamp-on meters and multimeters. Clamp-on meters are widely used because of the ease of operation. Multimeters are also extremely popular because they are easy to carry and are capable of performing a wide variety and range of measurements. A large number of attachments for these units are available, so that they can be used for measuring light levels, temperature, and other variables to further expand their usefulness to electrical personnel. Most are available with either digital or analog readouts, the choice depending largely on the personal preference and accuracy requirements of the user.

Both clamp-one and multimeters can be average responding or true-rms types. The true-rms units respond to the effective heating value of an AC waveform. An averaging meter calculates the arithmetical mean of the waveform. When the signal to be measured approximates a pure sine wave, either an average responding or true-rms meter can be used with reasonable accuracy. However, if the waveform is distorted, such as is common in circuitry powering phase-to-neutral and phase-to-phase nonlinear loads, then the true-rms sensing device is preferred because the reading will be more accurate.

Portable test equipment

Megohmmeters, including specialized versions to determine the resistance of grounding systems, are also widely applied. They can be hand-cranked or battery-operated and are available in various degrees of sophistication.

Recording-type instruments have proven to be extremely helpful for analyzing system parameters such as current, voltage, electrical noise, wave shape, and many others, over a long period of time. This type of equipment ranges from relatively simple dot-matrix printers to high-speed computerized units.

Harmonic analyzers have become extremely important as more nonlinear loads become the norm in today's office and factory.

Thermal measuring instruments also are quite popular as a means of detecting overheating in electrical system equipment. These instruments range from simple units that provide a direct readout on a meter of scale, to highly complex instruments that provide thermograms (infrared-created photos) that show precisely where hot spots are located. Infrared sensing devices are excellent for finding loose connections, corroded fuse clips, deteriorated splices, and other potential trouble spots that generate heat.

Larger, portable test equipment includes high-current test sets used to check the operation of power circuit breakers, relay test sets for accurately adjusting the settings of protective relays, and high-potential test sets to evaluate the conduction of medium voltage cable. Specialized equipment is used for making power factor tests on large motors and transformers.

Bench test equipment

Laboratory-type equipment is also available, for example, for the analysis of oil samples of transformers. Gas chromatographs are used to detect minute traces of various materials, such as PCB. Highly accurate oscilloscopes, counters, and other bench equipment are also widely used in conjunction with electrical installation and equipment testing.