Current Tips on Current Clamps

If you ever need to measure electrical current without shutting down your power system, you can appreciate the useful utility of a current clamp or “clamp meter.” These indispensable tools combine current and voltage measurements with an integral digital display in a handy and easy-to-use piece of test equipment.

Clamp meters meet a specific set of requirements. They are fast and easy to detect AC and DC electrical problems where it is often difficult, or impossible, to turn off the system. To use a clamp meter, you simply clamp the jaws around the conductors of a circuit and the built-in digital display will read the appropriate values. There is no need to turn off the circuit, alter the operation or remove any insulation. It’s that simple.

Basic Types
There are two kinds of clamp meters now commonly available: “average responding” and “true-RMS” sensing. The difference between the two is simple. While the average responding units are widely used and are usually lower in cost, they give correct readings for linear electrical loads — such as residential electrical systems with standard induction motors, resistance heaters, and incandescent lights. But when the loads are nonlinear, containing semiconductors — as with personal computers, photocopiers, energy efficient lighting, commercial air conditioning units or with adjustable frequency drives — the average responding meters typically read low — perhaps as much as 40 percent in error.

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