Clamp Meter Usage

If you want to measure current, voltage, etc., you need specialized measuring equipment. Analog and digital multimeters are usually used to measure current, but the circuit must be cut off and the multimeter and the circuit connected in series in order to make the measurement. However, it is not uncommon that the circuit cannot be disconnected under certain circumstances. In addition, there is a danger of electric shock when the circuit is disconnected.

In this case the clamp meter will come in handy. In this article, we will introduce the use of clamp meter and precautions in detail.

■ Definition of Clamp Meter

A clamp meter is a measuring instrument, similar in shape to a clothespin, that measures current by holding an energized wire. The principle of measurement is to measure current by means of a sensor that captures the magnetic field that occurs from the current and converts it to current.

The advantage of a clamp meter is that, unlike a measuring instrument such as a multimeter, there is no need to disconnect the circuit to be measured when measuring current. Clamp meters can be broadly categorized into two types.

Load current measurement type

Leakage current measurement type

In addition to this, further details are categorized according to the differences in "whether DC and AC currents can be measured" and "whether the average or true RMS method is used when converting AC to RMS". For general AC circuit measurement, the load current measurement type should be used. In recent years, some clamp-on meters can measure both load current and leakage current.

■ Basic use of a clamp meter

In this article, we will briefly introduce the load current measurement type and leakage current measurement type.

・The common point load current measurement type and leakage current measurement type can be used in basically the same way. First of all, if the clamp meter has a DC-AC selectable type, set it according to the object to be measured. In addition, switch the measurement range according to the amount of current. Please keep in mind that when measuring DC current, zeroing is required first.

Wires are located in the center of the clamp meter	Wires off center of clamp meter

Wire at center of clamp meter Wire off center of clamp meter

When ready, open the jaws of the clamp meter and hold it over the wire to be measured. Placing the wire in the center of the clamp allows for more accurate measurements.

・How to use the load current measuring clamp meter When using the load current measuring clamp meter, only one wire must be clamped. Please note that if more than one wire is clamped at the same time, it will not be possible to measure correctly.

Leakage Current Measurement Type Clamp Meter

Care must be taken with leakage current measuring clamp meters. Only one ground wire can be clamped. Whereas AC wires need to be clamped all the way (2 single-phase, 3 three-phase). When measuring leakage current, 2 wires can be clamped at the same time. Leakage current is the current that flows to earth through the insulation resistance of a load, which is normally less than a few μA, but may reach tens of μA if a number of loads are connected.To measure leakage current with a clamp-on ammeter, clamp the two wires together and check the small difference between the two wires, which is measured as the leakage current.

■ Precautions for the use of clamp meters

Like analog and digital multimeters, clamp-on meters require care when used. If the jaws are left connected after use, there is a risk of malfunction in the event that too much current flows through the clamp sensor, so care needs to be taken.

In addition, for safety reasons, clamp-on meters must not be used to measure current on bare conductors, but only on insulated conductors, depending on the current sensor.

Clamp meters are safe because they do not require disconnection of the circuit, but should not be used to exceed the maximum rated voltage to ground. In addition, the guard of the clamp meter is used to indicate the safety limit; do not touch the jaw end of the front of the guard during use.

■ Methods of selecting a suitable clamp meter

As mentioned above, there are various types of clamp meters for different applications such as DC and AC. Therefore, it is necessary to select the appropriate clamp meter based on the object to be measured. For example, measurements of automotive and solar batteries and uninterruptible power supplies (such as UPS) require clamp meters capable of measuring DC currents.

On the other hand, an AC clamp meter is required for measuring load and leakage currents in AC power distribution circuits such as lights and wires in ordinary homes, buildings and factories. For normal measurements, a load current measuring type AC clamp meter is preferred, while for measuring leakage currents due to poor insulation or currents flowing in the grounding wires of electrical equipment, etc., a leakage current measuring type AC clamp meter is preferred.

■ Safe use of clamp meters

A clamp meter is a convenient measuring tool that can measure current and other parameters by simply clamping the wire under test without disconnecting the circuit. The basic use of a clamp meter is to measure by simply clamping the wire under test, making it both safe and convenient to use. However, it can also be dangerous if not used properly. Therefore, please refer to the usage, precautions, and selection of clamp meters described in this article to ensure safe use.