What Is a Multimeter? Multimeter and Clamp Meter Guide
A multimeter is a test instrument that measures quantities such as voltage, current and resistance with one device; this guide covers clamp meters, True RMS and CAT selection.
What is a multimeter and where is it used
A multimeter is a test instrument that measures more than one electrical quantity, such as voltage, current and resistance, with a single device. Digital ones are called DMMs (digital multimeters); some models also offer additional measurements such as capacitance and temperature. A clamp meter is a device that measures current without opening the circuit, using its clamp-shaped jaws; some models also offer voltage and resistance measurement. They are used in electrical panels for troubleshooting, maintenance, commissioning checks, automation and electronic service work.
Types of multimeters and clamp meters
The category is divided into two subgroups:
- Digital Multimeters (Handheld and Benchtop): Digital multimeter models such as Unit UT33A+, UT39C+, UT58A, UT136C+, UT151C, UT191T and UT890C are here, along with the UT122, which is called a smart multimeter.
- Clamp Meters: Models such as the UT220 and UT2117R, which measure AC current, and the UT216C and UT256, which are listed as AC/DC True RMS, are listed along with examples that have an open-jaw structure.
What to look at when choosing a multimeter
- Measurement functions. Voltage, current and resistance alone may be enough; if you need additional functions such as continuity, capacitance or temperature, check that they are written on the device's product page.
- True RMS. Loads such as variable-speed drives, electronic ballasts and computers can produce waveforms far from a sine wave. In such circuits, a device listed as True RMS is preferred.
- Measuring range and accuracy. The voltage, current and resistance ranges in the manufacturer data must cover your work. On a clamp meter, the upper current limit (for example, models with 60 A, 600 A, 1000 A or 2000 A in the product name) is the main distinguishing factor.
- AC or AC/DC current. A clamp that measures only AC current and a clamp that measures AC/DC serve different jobs; if direct current will be measured, for example on batteries or DC supply lines, an AC/DC model is needed.
- CAT category. The device is chosen according to the highest measurement category in which it can be used, and its voltage rating must match or exceed these conditions. Category and voltage are separate values; they are read together.
- Use environment. For field and panel work, a handheld or clamp device is suitable; for laboratory and service benches, a benchtop type is suitable.
How to read the measurement category (CAT)
The CAT II, CAT III and CAT IV marking on the device shows in which part of the circuit the device is designed to be used. In manufacturer documents, CAT II describes loads connected to a single-phase socket, CAT III describes three-phase distribution (including switchgear in fixed installations and busbars and feeders in industrial plants), and CAT IV describes the mains connection point and outdoor line conductors. Which category and voltage are required is determined according to the project and the manufacturer data of the installation; measurement on an energized circuit must be carried out by an authorized electrician. Also look in the product documents for a mark showing that the device has been tested by an independent laboratory.
The difference between a multimeter and a clamp meter
A multimeter works with test leads. A clamp meter, on the other hand, measures current without opening the circuit, by taking the conductor inside the jaw. For this reason, the two devices are used not as substitutes for each other but as complementary instruments. For measuring instruments fixed-mounted in a panel, Panel-Mount Multimeters are suitable; for portable measuring instruments, this category is suitable.
Complementary measuring instruments
Insulation Resistance Testers for insulation condition, Earthing Measuring Instruments for earthing, and Energy Analysis Instruments for power and energy analysis are device groups designed for separate measurement jobs. For the whole parent group, see the Measuring Instruments page.
The brand in this category
All products in this category are of the Unit brand. The list covers digital multimeters, True RMS models and clamp meters that measure AC and AC/DC current.
Ordering notes
Products are sold by the piece. Some products are listed as "made to order" (terminli); for these products, the lead time is confirmed during the order process. You can reach a product from its model number by searching with the stock code.
Comparison and selection table
| Selection Criterion | Digital Multimeter (Test Lead Probe) | AC Clamp Meter | AC / DC (Hall-Effect) True RMS Clamp Meter |
|---|---|---|---|
| Current Measurement | In-series via test leads (typically up to 10 A fused) | Non-contact jaw around a single conductor (AC current) | Non-contact jaw measures both AC and DC current (400–1000 A) |
| Voltage & Diagnostics | High-resolution AC/DC V, mV, Ω, diode, capacitance, Hz | AC/DC voltage, resistance, continuity + high AC current | True RMS AC/DC V & A, motor inrush current, temperature |
| Best Suited For | Control wiring, PLC I/O, PCB & precision troubleshooting | Fast load checks on live AC feeders & distribution panels | Solar PV DC strings, battery banks, UPS, EV & VFD service |
| Safety Category | CAT III 600 V / CAT IV 600 V (HRC fused current jacks) | CAT III 600 V, 25–45 mm jaw opening | CAT III 600 V / 1000 V with DC Zero calibration button |
Frequently asked questions
Which quantities can be measured with a multimeter?
A multimeter basically measures voltage, current and resistance. Depending on the model, additional functions such as continuity, capacitance and temperature may also be available. Which functions and which ranges are available is written in the technical data on the device's product page; compare this data according to your job when choosing.
How is a multimeter used, and what should be watched for?
In use, the manufacturer's manual is the basis; the function and test lead input suited to the quantity being measured vary by device. The device's CAT category and voltage rating must suit the circuit being worked on. On energized circuits, the measurement method is determined according to the project and the manufacturer's instructions, and the work is done by an authorized electrician.
What is a clamp meter, and how does it differ from a multimeter?
A clamp meter is a device that wraps its jaws around a conductor and measures current without opening the circuit. A multimeter, on the other hand, works with test leads. Some clamp models also measure voltage and resistance; the two devices complement each other according to the job they do. Which quantities are measured is written in the model's technical data.
What is True RMS for, and is it needed for every job?
True RMS aims to display the effective value correctly for waveforms far from a sine wave. It becomes important in circuits with loads such as variable-speed drives, electronic ballasts and computers. Whether it is needed is decided by looking at the load to be measured and the device's technical data.
What do multimeter CAT II, CAT III and CAT IV mean?
CAT is the measurement category that indicates the part of the circuit in which the device will be used. In manufacturer documents, CAT II describes single-phase loads connected to a socket, CAT III describes three-phase distribution and fixed-installation switchgear, and CAT IV describes the mains connection. The device is chosen according to the highest category and voltage in which it can be used.
Is there a difference between an AC clamp meter and an AC/DC clamp meter?
AC models measure only alternating current, while AC/DC models measure both alternating and direct current. For direct current measurements such as batteries and DC supply lines, an AC/DC model is needed. Product names in the category such as Unit UT216C and UT256 are listed as AC/DC True RMS; for details, see the product page.