How to Determine Amperage Clamp
Electrical engineers and technicians use amperage clamps (or current clamps) to measure the current from a cable without having to disconnect the cable. This is valuable, given that it may not be practical to disconnect a cable. The clamp has two jaws that open to clamp around the cable, achieving 360-degree coverage. As current flows through the cable, it produces a radiated signature, which the clamp picks up and records. You choose or determine which type of clamp to use based on the type and amplitude of the current.
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Instructions
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1
Determine whether the current you want to measure is alternating current (AC) or direct current (DC). Refer to circuit diagrams or schematics. In general, if your system is powered directly from the utility company via a wall outlet or distribution box with no other power supply that alternates circuitry (such as a rectifier bridge), then you are measuring AC current. However, if the schematic shows a rectifier bridge or diode bridge connected to the main power source, then the AC is converted to DC, and you will be measuring DC current.
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2
Find the current rating for the circuit. Refer to circuit schematics or the design requirements of the circuit. If you can't find the current rating but you find the power rating in Kilowatts (KW) and the voltage rating, you can calculate the current rating using the formula I = (KW * 1000)/V where I is current, KW is power and V is voltage. For example, if KW is 200 watts and V is 480 volts:
I = (200 * 1000)/480 = 416 amps.
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3
Choose and purchase a current clamp based on the information from Step 1 and Step 2. For example, most current clamps work better with an AC current level of 1,000 amps or more. If you have DC current or low AC current levels, as in milliamperes, these currents are hard to measure. Therefore, in these cases, ensure you find a clamp that can measure under these conditions.
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