A Clamp Meter (Clamp Meter) is a portable meter that measures the current in a circuit by measuring the magnetic field strength around a single conductor.
The clamp meter is used to measure current in a circuit with currents greater than 1A and in applications where it can be easily placed around one of the conductors. Voltage and resistance can also be measured with most clamps. To measure voltage and resistance, the test leads must be connected to the clamp and they must have a voltage and resistance measurement mode.
In addition to the basic measurement functions (current, voltage and resistance), some of these clamps also include functions such as a HOLD button to maintain the displayed measurement, a min / max button to record the minimum and maximum, measured values, and other special functions.
Current is a standard measurement parameter for troubleshooting purposes because an electrician can only use current measurement to determine how much a circuit is loaded (or running). Current measurements are different because the current can vary at different points in parallel or series-parallel circuits. The current in series circuits is constant throughout the circuit. When parallel loads are added to the circuit, the supply voltage remains the same, but the current must increase with each added load.
The highest amperage in the parallel circuit is at the point closest to the power source. The further away from the power source, the current decreases as the system distributes current to each of the parallel loads. On a separate branch of the series-parallel circuit, the current flowing to the load (motor, heating element or light bulb) is the same as the current in the return line from the load. A small difference in measurements (up to 10%) between the lines is possible when using a clamp meter due to the location of the meter or when measurements of low currents are performed with large ammeter ranges (measurement 2 A at a setting of 400 A). Any excessive deviations should be investigated as current measurement may indicate a partial short circuit on one of the lines when current flows to ground.
Ohm's Law states that the current (I) in a circuit is equal to the voltage (U) divided by the resistance (R). To calculate the current according to Ohm's law, apply the formula: I = U / R. For example, let's find the current in a wire with a resistance of 5750 Ohms and an applied voltage of 115 V. I = U / R = 115/5750 = 0.020 A = 20 mA.
When measuring current in a circuit supplying multiple loads, the current may not be the same on each line. When current measurements are taken from the main power panel or from the motor drive, the current in the hot and neutral conductors of a 115 V or 208 V single-phase circuit and in all three phases of circuit 3 (Ï•) should be substantially the same.
A clamp meter measures the current in a circuit by measuring the magnetic field strength around a single conductor. To prevent stray magnetic fields from being detected during testing with the clamp, electricians should separate the tested conductors from other wires as far as possible. When measurements can be influenced by stray magnetic fields, it is necessary to make several measurements along the conductor at different locations.
If you plan to measure AC or DC current with a clamp meter or the multimeter that the clamp meter is connected to, be sure to follow standard procedures. Before making any current measurements with a clamp meter, make sure the Meter is rated to measure on the circuit under test. Refer to the test setup instruction manual for all precautions, limitations, and measurement procedures. Always use the necessary personal protective equipment and follow all safety precautions when taking measurements. To measure current with a clamp meter, follow these procedures:
- Determine if the current in the measured circuit is DC or AC.
- Select an appropriate clamp meter for measuring circuit current (AC or DC). If both AC and DC current measurements are required, select a clamp that can measure both AC and DC currents.
- Make sure the current range of the clamp meter is high enough to measure the maximum current that exists in the circuit under test.
- Set the clamp meter function switch to the maximum current position (600A, 200A, 10A, or 400mA). Select a setting equal to or greater than the maximum possible loop current if there is more than one test position or if the loop current is unknown.
- Open the measuring jaw by pulling the trigger.
- Insert one wire into the center of the clamp. Make sure the clamp is fully closed before taking any current measurements.
- Read the current measurement displayed on the clamp meter.
- Remove clamp or other clamping devices from the chain.
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