Resistance – Resistance is measured in ohms (Ω). Resistance values can vary widely, from a few milliohms (mΩ) in the case of resistance between contacts, to trillions of ohms in the case of insulators. Most current clamps measure down to 0.1 Ω. When the measured resistance is higher than the upper limit of the instrument, or the circuit is open, “OL” is shown on the display. Resistance measurements must be made with the circuit not energized, otherwise the circuit or the clamp itself may be damaged. Some clamps provide ohm mode protection in the event of accidental contact with voltages.
Continuity – For continuity, a quick walk / close test of the resistance is performed that distinguishes between an open and closed circuit. A current clamp with an acoustic continuity signal allows you to complete numerous continuity tests easily and quickly. The multimeter emits a sound when it detects a closed circuit, with this the user does not have to see the equipment while taking measurements. The level of resistance required to activate the sound varies between different meters. The typical resistance setting to activate the acoustic signal is a reading below the 20-40-ohm range.
Measurement of current – One of the most basic measurements of a clamp meter is current. Current clamp meters can measure both AC and DC current. Typical current measurements are made in various branch circuits of an electrical distribution system. Determining how much current flows in the various branch circuits is a very common electrician task.
Voltage Measurement – Current clamp meters can measure both AC and DC voltage. AC voltage is typically created by a generator and then distributed through an electrical distribution system. An electrician’s job is to be able to take measurements through the system to isolate and troubleshoot electrical problems.
The ability of a clamp meter to measure AC voltage can be affected by the frequency of the signal. Most clamp meters can accurately measure AC voltages with frequencies from 50 Hz to 500 Hz, but the AC measurement bandwidth of a DMM could be 100 kHz or higher. For this reason, reading the same voltage with a clamp meter and a digital multimeter can provide different results. The DMM distributes most of the high-frequency voltage across the measurement circuits, while the clamp meter filters some of the voltage contained in the signal above the multimeter’s bandwidth.
How to choose the ideal team
When purchasing a clamp meter, not only do you need to look at the specifications, but you should also look at the features, functions, and overall design value of the instrument, as well as the quality and reputation of the brand. Measurements made with these tools can be highly dangerous if you work with equipment of dubious quality.
User safety is the most important when choosing a clamp meter or any other instrument. Few brands, testers are independently tested and certified by recognized labs like CSA, TÜV, etc. Only with these approvals can you be sure that your tools meet the latest safety standards.
After verifying the reliability of the tool brand, it must be identified that it is to be measured with it. This will give you the values you need to measure and also the resolution. In the market there are clamps of many prices and these differ in many features, one of the most important is resolution. The accuracy of a clamp meter is normally expressed as a percentage of the reading. An accuracy of 3% in the reading means that at a reading of 100 amps, the actual value of the current can be between 97 and 103 amps.
One of the limitations of clamp meters is usually voltage. There are 600V and 1000V depending on the quality of it. It is important to know if we are going to work with voltages higher than 80% of what it can measure, that is, if we are going to work with 480V in three-phase, we need a clamp that is CAT II 750V or 1000V for an accurate reading. If the voltage is too high, the clamp will not be able to give an accurate reading.
For electricians working with motors, the ability to capture the amount of current a motor draws at start-up can be an excellent indicator of motor condition and load. The 374FC, 375FC, 376FC clamp meters incorporate starting current measurement as part of their feature set. After placing the clamps (or the flexible current probe) on one of the motor inputs cables, activate the start current mode. Then start the engine.