Solutions for Every NeedA clamp meter is an electrical tester that combines a voltmeter with a clamp type current meter. Like the multimeter, the clamp meter has passed through the analog period and into the digital world of today. Created primarily as a single purpose test tool for electricians, today's models have incorporated more measurement functions, more accuracy, and in some instruments, some very special measurement features. Today's clamp meters have most of the basic functions of a Digital Multimeter (DMM), but with the added feature of a current transformer built into the product.
The ability of clamp meters to measure large ac currents is based on simple transformer action. When you clamp the instrument's "jaws" around a conductor carrying ac current, that current is coupled through the jaws, similar to the iron core of a power transformer, and into a secondary winding which is connected across the shunt of the meter's input. A much smaller current is delivered to the meter's input due to the ratio of the number of secondary windings vs. the number of primary windings wrapped around the core. Usually, the primary is represented by the one conductor around which the jaws are clamped. If the secondary has 1000 windings, then the secondary current is 1/1000 the current flowing in the primary, or in this case the conductor being measured. Thus, 1 amp of current in the conductor being measured would produce 0.001 amps or 1 milliamp of current at the input of the meter. With this technique, much larger currents can be easily measured by increasing the number of turns in the secondary.
Buying a clamp meter not only requires looking at specifications, but also looking at features, functions, and the overall value represented by a meter's design and the care taken in its production. There are many types of clamp meters. Choosing the one that best suits your applications is important. A brief overview follows, for a more in-depth look see 5 things to consider when buying a clamp.
- Use a basic clamp meter to ensure all three phases on your feeders are pulling the same current.
- An advanced clamp meter with some logging capability, will help you resolve intermittent breaker trips.
- You might need a specialized clamp meter that can accurately measure motor inrush current. You'll want a specialty clamp if you do motor maintenance on production conveyor motors, HVAC motors, and plant air compressors, knowing motor inrush current is crucial for keeping these systems running.