The term “current clamp” can be used interchangeably with other terms such as “current clamp meter” or “current probe.” Current clamps are specially designed for use by tradesmen and technicians in the heating, ventilation, and/or air-con technology sectors. In the US, these devices are also known as Amp Clamps.
They allow technicians to fasten the probe portion of the device to a conductor without removing or rerouting cables. You don’t have to disconnect the cables to insert them into the probe, and neither do you have to make physical contact with cables. This helps you read and measure the magnitudes of AC and DC and the waveform and current phase shift.
Clamp technology has several useful functions and features.
Before we explore these aspects, it’s important to know more about current clamps and clamp technology.
What Are Current Clamps?
Current clamps (also known as current meters or current probes) measure electrical current that passes through a conducting medium. They provide readings on voltage, resistance, continuity, capacitance, etc.
The measurement is read in amperes. They fall into two main categories: those designed to measure load current and those designed to measure leakage current.
The device is designed quite similarly to a regular clamp, or a clothespin, with a pair of jaws that can be opened to hold the cable/conducting medium, bus-bar, or wire securely while the readings are taken. The output is in analog form, and it can be read by oscilloscopes, voltmeters, power analyzers, or a data acquisition system (DAQ). There may be a display on the clamp or probe too.
The current clamp’s wide jaws help hold the conducting medium in place and analyze live conductor fields safely without disruption or interruption of the circuit.
Current probes and clamps use the Hall Effect to measure magnetic fields in a non-contact method.
You can use as many wires or cables as you want as long as they fit properly into the clamp. However, it does not differentiate between wires, and the reading will be a sum of all the wires that have been inserted into the clamp. If two wires with current flowing in opposite directions are inserted into the clamp, the reading will be the difference between the two.
A majority of clamps are in the range of one-inch aperture. They usually measure current between 10-100 amp, but clamps with larger apertures are also available to measure current between 250amp and 20-kilo amp.
There are several different types of current clamps:
Current transformer clamp: This is a passive transformer. It bypasses the traditional method that electricians used earlier by cutting a wire and inserting a probe to measure in-line current. The transformer clamp can only be used to measure AC or waveforms and is not considered perfectly accurate. It consists of a ferrite/soft iron split ring with a coil surrounding one or both parts. This becomes one half of the winding, while the other half of the winding makes up the other part. It can also be used to inject current into the conducting medium to insert interference current.
The flexible current probe or Rogowski Coil: is also used to measure AC only. This device uses lightweight measuring heads. It is based on the Rogowski Principle. The advantage of this clamp is that you can use it to get to hard-to-access areas. It creates a magnetic field and provides voltage readings proportional to the rate of change of current passing through the primary cable. You will need additional signal processing before the values can be displayed. It doesn’t require electrical/magnetic contact at the open end.
Open Loop Current Clamp: They usually measure both AC and DC up to 1000s Hz. This device is similar to the transformer clamp, but it has a magnetic core and a gap/slit cut into the core. The magnetic field generated by the conductor is concentrated across the gap.
Closed-Loop Current Clamp: is a current sensor with a fixed aperture so that it doesn’t open. They offer higher linearity, stability, and accuracy when compared to open-loop types.
Coreless Current Clamp: can be compared to the Rogowski Coil. It has a row of sensors that takes samples of the current passing through the conducting medium, calculates the field, and provides an output measurement. It works well in harsh environments and, being flexible, can be used to access difficult areas.
What Are Current Clamps Used For?
The main use of the clamp is in situations where it is not feasible or impossible to disconnect the live power supply to the conducting medium. Hence, the electrical device or appliance can continue to work even while the measurements are being taken.
Current clamps can be used in several fields such as residential, commercial, industrial, electrical, manufacturing, construction, etc.
Typical uses include:
- Measure electrical power and energy, AC and DC within a set range
- Restoration/Fixing electrical connections in existing electrical systems/devices without cutting power supply
- Swift and accurate reporting of malfunctions as well as potential problems
- Can be used in applications connected to industrial controls and equipment, commercial/residential electrical systems, HVAC
- Installation and trouble-shooting new or malfunctioning devices
- Supervision of general functioning of electrical circuits in regular maintenance and testing
- Estimation and calculation of leaks and current interference
- Measurement of current flow rate and capacity at distribution panels
- Perform/Execute maintenance procedures
- Manage devices that may be vulnerable to damage
- Aid beginner electricians during the fitting of electrical instruments
- Repairing accessible systems without interruption of power supply
Care of Current Clamp
Current clamps are expensive, and they are a long-term investment that can serve you well for years. However, it’s important to take care of them and maintain them in good condition to remain efficient and provide accurate results.
They should be stored safely and properly in a clean, dry place. This will ensure that the metal parts don’t rust. It is also important to keep them clean and free of dust, grease, and grime. Otherwise, you will not get correct readings.
Ensure that they are kept separately without placing weights on top of them. If the jaws of the clamp go out of alignment, they lose the magnetic circuitry. Most good models have self-aligning jaws, but it’s wiser to take precautions to store the device properly.
Never use the clamp in place of regular pliers or clamps. This can damage the device and its capacity to measure electromagnetic current.
