Current Clamp

An current clamp is a measuring device that can be used to measure current indirectly. It is therefore not necessary to interrupt the circuit for the measurement. The current clamp is usually easily recognisable by their pincer-like measuring element. For the measurement, the measuring clamp must be opened and placed around the current-carrying conductor. With the clamp closed, the amperage is then determined based on the strength of the electromagnetic field created around the electrical conductor. Since the resulting fields are very different for direct and alternating currents, different principles are used in the ampere clamp to measure direct and alternating currents. If direct currents are also to be measured, the attention must be paid when selecting the current clamp that it is also suitable for this purpose. It is often useful to check not only the amperage but also the other electrical parameters immediately. If an ampere clamp offers the functions of measuring the additional parameters to be determined, then no additional second device is needed on site. This is a great advantage, especially when the access to the measuring point is difficult and space is limited.

The following criteria should be taken into account when selecting an current clamp:

- Measurement for alternating current only or for direct and alternating current.
- Measuring range and resolution - Overvoltage category and maximum voltage value
- Design because of the measurable cable cross-sections
- Additional measuring functions
- Display options
- Memory and data transfer options

Measuring ranges and designs of current clamps
The current clamp can measure either alternating current only or alternating and direct current. Depending on the area of application, they must be designed for certain current values. For example, there are versions that can only measure up to a maximum of 2 amperes and the others are for the amperage of up to 200 amperes, 600 amperes, 1,000 amperes or 3,000 amperes. In the case of an ampere clamp with a high maximum value, this measuring range is usually subdivided into different sub-ranges. The measuring range selection can be automatic or manual. Often, exceeding or falling below the measuring range is indicated on the display and, if necessary, the ampere clamp can be adjusted to the appropriate measuring range. As a rule, the higher the amperage is, the larger the wire cross-section.

The size of the clamp's opening is a decisive factor in determining up to which cable diameter the ampere clamp is suitable. Simple versions with a fixed fork can only be pushed onto the cable and then closed. The Ampere clamp with movable legs is usually easier to handle and close around the circular cables. For particularly large cross-sections, there is a special solution for AC current measurement, the Rogowski coil. The Rogowski coil is a flexible cable that is laid in a circle around the line to be measured instead of the clamp legs.

Overvoltage categories for the current clamp
To avoid accidents caused by the voltage peaks, only use the current clamp that has overvoltage protection appropriate to the area of application. According to DIN EN 61010 or IEC 61010, there are four overvoltage categories: CAT I, CAT II, CAT III and CAT IV. The lowest category CAT I is suitable for the measurements on mains-independent circuits that are supplied, for example, by batteries. The CAT II category applies to circuits that are supplied by the low-voltage mains via plugs and the CAT III category – to stationary consumers and distribution connections. An current clamp belonging to the highest category CAT IV is also suitable for the measurements on meters and main connections of the low-voltage installation. The maximum voltage value of 300 volts, 600 volts or 1,000 volts specified for the current clamp indicates the voltage peaks that may reach the device.

Additional measuring functions with the current clamp
Many models of the ampere clamps offer the functions of a multimeter besides the indirect measurement of the amperage. They are supplied with additional measuring tips or measuring clamps and are operated exactly like the multimeter for these measuring functions. In addition, some types of the current clamp are also equipped with one or more temperature sensors to measure temperatures. Many models also have a handy torch function to illuminate dark areas. More specialised functions include, for example, non-contact voltage and frequency testing for alternating current, power measurements and leakage current measurement. Device types with three or four measuring clamps allow simultaneous measurement of several phases.

There is a special function for measuring and evaluating the start-up behaviour of machines, the inrush function. When this function is activated, the current clamp measures as soon as it detects a current in very short time intervals in order to record the maximum value of the starting current. The highest measured value remains on the display as the peak value, even if the current drops.

Display types for current clamp
The display of the current clamp is also important for the functionality when measuring and evaluating. There are many different types, ranging from single-line displays that show the measured value in a large, high-contrast format, to the displays showing up to ten measured values at the same time, or graphic displays that show simple or detailed curves. It is important that the display of the device shows the desired data clearly and in sufficient detail, both during the measurement on site and later for the evaluation.

Memory and data transmission in the current clamp
If the measurements are to be documented and evaluated, it makes sense to choose the current clamp that can store the measurement data in the device or on a removable data carrier. The memory contents can then be retrieved later and transferred to operating books or a computer programme. In this way, the course of values can be evaluated and the causes of irregularities can be clarified more easily.

When it comes to storage options, a distinction must be made between the stored individual values and the measurement series in which the measurements are taken repeatedly at fixed intervals of equal length. The devices that allow automatic measurement and storage at a fixed cycle time are called data loggers. For an current clamp with the data logger function, an attention should be paid to which cycle times can be set and how many data sets can be stored. In addition, some models have various options for setting the start and end of the measurement series.

The current clamp is usually equipped with a USB interface for transferring the stored measurement data. However, there are also device versions where the values can be conveniently transferred to a smartphone, tablet or PC via Bluetooth.

Other current clamp meters have features for measuring parameters such as AC/DC voltage, resistance, continuity, capacitance, frequency, power factor and temperature. For many contractors working in the field, a multipurpose tool is desirable to help streamline the contents of their toolboxes. Current clamps can be found in our PCE Instruments pamphlet here (PDF, 1.8 MB).

Should you require additional assistance in selecting a current clamp product, please don’t hesitate to contact the PCE technical support staff at or +44 (0) 2380 987 035 for PCE Instruments UK, or at or +1 (561) 320-9162 for PCE Americas Inc.