Thorough and regular testing is crucial for the safety of anyone who may come into contact with electrical equipment. One crucial tool is the clamp meter—a device for measuring current.
In this article, we’ll dive into what clamp meters do, how they work, and their common industry applications.
What is a clamp meter?
A clamp meter, also known as a current probe or current clamp, is an electrical testing tool combining a current sensor with a basic digital multimeter.
Clamp meters are typically clothespin-shaped with jaws that wrap around live wires to measure the current travelling through. Digital multimeters are similar tools, although they focus on measuring voltage with some current-measuring capabilities, while clamp meters do the reverse—measuring current with some voltage-measuring capabilities.
Common types of current clamps include:
- Flexible (AC)
- Current transformer (AC)
- Hall Effect (AC and DC)
Flexible clamp meters have no iron core. They use a helix-shaped coil that responds to the first derivative (or rate of change) of a conductor’s magnetic field.
Current transformer and Hall Effect clamp meters do have an iron core, but Hall Effect meters do not have copper wires wrapped around their jaws. Instead, the conductor’s magnetic field focuses across a gap in the core after clamping.
How clamp meters work
To measure current, clamp meters detect the magnetic field the current emits as it flows through a wire. Technicians can clamp the device’s jaws around a cable or wire at any point in the system, measuring the current without de-energising or disconnecting the circuit.
Underneath the plastic moulding is a set of hard, ferrite iron jaws designed for detecting, concentrating, and measuring a current’s magnetic field. Most varieties have additional features including:
- A tactile barrier to prevent electric shocks,
- A hold button to freeze the display reading (and release it when pressed a second time),
- A MIN/MAX button to display the minimum and maximum input,
- A zero button to remove the DC offset from any DC measurements,
- Alignment marks to ensure accuracy,
- Common and volts/ohm input jacks,
- Input for a current probe.
Clamp meters have a current range of zero to 100 A at a minimum and as high as 2,500 A at a maximum. This factor makes them an excellent choice for measuring high current levels (as opposed to digital multimeters, which may become damaged under the same circumstances).
Industry applications of clamp meters
Clamp meters are useful for testing all sorts of electrical equipment, from industrial controls to commercial electrical systems and HVAC.
You might use one to repair existing systems, troubleshoot problems, and perform scheduled maintenance. They’re also a go-to tool for performing final circuit tests and supervising apprentice electricians as they install equipment.
To summarise
Clamp meters are a reliable tool for measuring high current levels and maintaining workplace safety. To summarise, they work by detecting the magnetic field emitted by the current as it passes through a cable or wire, converting the measurement into a visible reading on the device’s digital display.
