Clamp-on Ampmeters

(Scroll down to see different brands compared)

 

Clampmeters are helpful  electrician's tools, with an inductive current clamp built-in.

 If you measure AC and/or DC currents often, a clamp-on meter

• simplifies current measurement, 
• increases  safety,  
• and is tailored for electrical and HVAC work. 

The semi-circular head of a clamp-on amp meter contains either a coil of wires (AC-only clamps) or an electronic sensor (most AC/DC clamps) that pick up the magnetic field generated around a wire when electricity is flowing:  

AC Current Clampmeters jaws clamp around one wire of a two-wire circuit, inductively coupling the magnetic field into the tester's clamp. AC (alternating) current creates a strong magnetic field that reverses between positive and negative.

At 60 cycles per second in North America  (60Hz), the magnetic field reverses 120 times a second: once at the beginning of changing from one cycle to the next, and again in the middle of a cycle. This alternating magnetic field generates a voltage and current in a coil placed around the wire, just like an electrical transformer. 

DC  Current Clampmeters typically use an electronic, Hall-Effect sensor to pick up the weaker, non-alternating magnetic field generated by Direct Current flowing in a wire. 

DC does not alternate between positive and negative peaks, so a more sensitive electronic sensor is used for higher resolution, more accurate and repeatable measurements. 

DC current sensors are sensitive and susceptible to other magnetic fields in the area. For best results, hold the clamp head next the the wire to be measured, and adjust the "zero" control until the display reads "0000" before clamping the jaw around the wire and taking a measurement. 

Clampmeter sensors are placed around only one wire in a circuit

 

 

When the current clamp sensor head is closed  around both wires in a circuit, the two magnetic fields running in opposite directions cancel each other out, and we get "0000" reading on the meter. 

 

 

When the current clamp sensor is closed around one wire, only one magnetic field, in one direction, is used for the measurement, giving us the correct reading. 

A smaller loop around a wire will pickup more of the magnetic field than a larger loop. 

A tighter fit around the wire produces a more accurate, more repeatable measurement. 

"Repeatable" means the value does not change much from one reading to the next. This can be a bigger problem than you would think,  especially with lower quality  testers. 

To get the best reading, the current clamp sensor should either be tight against the wire, or the wire placed in the center of the loop. Most current clamps have target markings on the edges to show where to position the wire. 

This is a trade off when selecting an instrument: being able to measure different size wires verses how accurate the measurement is. For most electrical work,  measuring larger wires in power distribution cabinets is more important than a small difference in readings. Inductive measurements produce less accurate measurements than the in-line method anyway, and the dramatic increase in safety is worth the compromise. 

Some clampmeters include a smaller "amp tip" area on the current clamp sensor to overcome the trade-off  between versatility across different wire sizes and measuring current on small wires.  The amp tip area has higher sensitivity for lower currents.

This can be a  useful feature for electrical, industrial and electronic applications: having one tester instead of two or three current clamps with different size jaws. 

Inductive or Hall-effect sensor measurements of electrical current (flow in amps) are important safety and ease-of-use factor for these testers.

 Why use a Clamp-on Ampmeter or Accessory instead of a regular meter?

Because ClampMeters can measure 10's, 100's, and even 1000's of amps easily and safely.

Digital Multimeters can only measure up to about 10 amps directly, and can be a safety hazard in this mode if not safety rated. 

Electrical current flow is dependent on resistance,

• So the tester measuring  the current should not add any resistance into the circuit being tested.

In-line current measurement with multimeters minimizes resistance introduced into the circuit by the meter through special, fused  jacks with close to zero resistance (.3 ohms).

• Another description for zero resistance is a  "short circuit".
• A meter wired in series with the leads in the current input jacks is a short circuit,
  • which is why fused current inputs are important, to reduce risk if voltage is measured accidentally with the leads in the current inputs. 

​Please see the Electrical Measurement Safety Seminar Overview page found Here for more information on this.

 

Quick Links to Application Notes for Clamp-On Ampmeters (aka Clampmeters)

Safety considerations: 

ABC's of Electrical Measurement Safety app note : Are you working in a CAT III or CAT IV safety rating environment?

Fluke Application Notes: 

Clampmeter ABC's: What is a clampmeter and what can it do? 

Proper use of a clampmeter in commercial and residential settings

Why True-RMS is important with today's more electronic loads

Making accurate inrush current measurements (motor starting currents can be  5-10 times running current

Clampmeter solutions: Solving an overload trip on a motor

Troubleshooting 4-20mA HVAC control systems with a milliamp clampmeter

Better ways to troubleshoot automation and process control loops with milliamp clampmeters: no breaking the loop.

 

Digital Multimeter verses Clampmeter 

 

There are tons of different clampmeters out there. 

200 Amp to 400 Amp General Purpose Clampmeters

There are many brands of  Current Clampmeter test tools. 

Below are examples from the leading brands I have used in training classes, plus other manufacturers that have good reputations. 

As with any category of tester, the ability to take reliable, repeatably accurate measurements all day, every day, over many years is a feature of the units compared here. This requires high quality engineering, parts, and manufacturing processes. 

 

 

Fluke 323 True RMS AC Amps: 0-400A DC Amps: N/A AC Volts: 0-600V AC DC Volts: 0-600V DC Resistance: 0-4000 Ohms Audible Continuity Display Counts: 6000 Jaw Capacity: 1.1 in (28mm) Max Wire: 600 MCM Safety: CAT III 600V, CATIV 300V Base unit for 32X series   View/Buy on Amazon.com	Fluke 324 True RMS AC Amps: 0-400A DC Amps: N/A AC Volts: 0-600V AC DC Volts: 0-600V DC Resistance: 0-4000 Ohms Audible Continuity Display Counts: 6000 Jaw Capacity: 1.1 in (28mm) Max Wire: 600 MCM Safety: CAT III 600V, CATIV 300V Adds to Fluke 323:  Temperature: -14F to 752F Capacitance: 1,000 uFd Backlit DIsplay   View/Buy on Amazon.com	Fluke 325 True RMS AC Amps: 0-400A DC Amps: 0-400 A DC (adds to 324) AC Volts: 0-600V AC DC Volts: 0-600V DC Resistance: 0-4000 Ohms Audible Continuity Display Counts: 6000 Jaw Capacity: 1.1 in (28mm) Max Wire: 600 MCM Safety: CAT III 600V, CATIV 300V Adds to Fluke 323:  Temperature: -14F to 752F Capacitance: 1,000 uFd Backlit DIsplay Frequency: to 500Hz Min/Max Capture DC Amps View/Buy on Amazon.com     .

 

600 Amp General Purpose Clamp-on Current Multimeters

 

The " middle ground " for clamp-on ampmeters, with dozens of manufacturers, each producing a variety of models that can be confusing.

I've focused on the leading brands, products I personally used and trained electricians how to use, plus other manufacturers  that have good reputations.

As with any category of tester, the ability to take reliable, repeatably accurate measurements all day, every day over many years is a expected feature of the units compared here. This requires high quality engineering, parts, and manufacturing processes.

Many off-brand products are produced in the same contract-manufacturing factory in different colors, compared to companies like Fluke, Amprobe, AEMC and others who do their own designing, engineering, manufacturing and testing.   

Electric Motor / HVAC Focused Clamp-on Current Multimeters

The following is a sampling of clampmeters with functions specially designed for working on electrical motors and HVAC equipment.

These testers include all the capabilities of general purpose clampmeters, then

• add special functions to help test and troubleshoot motors and HVAC equipment,
• functions normally found on more expensive testers 

Special function examples include:

• Three-phase voltage rotation and measurement,
• Micro-amps for flame sensors,
• Higher capacitance ranges for larger motor starting capacitors. 

More manufacturers' examples being added as this site gets upgraded

Amprobe AMP-310 True RMS AC Amps: 0-600A DC Amps: N/A AC Volts: 0-600V AC DC Volts: 0-600V DC Resistance: 0-60,000 Ohms Audible Continuity Display Counts: 6000 Jaw Capacity: 1.2 in (30 mm) Safety: CAT III 600V Inrush for motor starting currents Special Low Amps measurement tip Micro-Amps (uA) for flame sensors Temperature: -42F to 752F Frequency to 999.9 Hz Capacitance to 2500 uFd (2.5mFd) Low Pass Filter for Motor Drives L1-L2-L3 Phase Rotation Testing Inputs View/Buy on Amazon	Amprobe AMP-320 True RMS AC Amps: 0-600A DC Amps: 0-600A (adds to AMP-310) AC Volts: 0-600V AC DC Volts: 0-600V DC Resistance: 0-60,000 Ohms Audible Continuity Display Counts: 6000 Jaw Capacity: 1.4 in (36 mm) >AMP-310 Safety: CAT III 600V Inrush for motor starting currents Special Low Amps measurement tip Micro-Amps (uA) for flame sensors Temperature: -42F to 752F Frequency to 999.9 Hz Capacitance to 2500 uFd (2.5mFd) Low Pass Filter for Motor Drives L1-L2-L3 Phase Rotation Testing Inputs View/Buy on Amazon	Amprobe AMP-330 True RMS AC Amps: 0-1000A DC Amps: 0-1000A AC Volts: 0-1000V AC DC Volts: 0-1000V DC Resistance: 0-60,000 Ohms Audible Continuity Display Counts: 6000 Jaw Capacity: 2.0 in (51 mm) Safety: CAT III 1000V, CAT IV 600V Inrush for motor starting currents Special Low Amps measurement tip Micro-Amps (uA) for flame sensors Temperature: -42F to 752F Frequency to 999.9 Hz Capacitance to 2500 uFd (2.5mFd) Low Pass Filter for Motor Drives L1-L2-L3 Phase Rotation Testing Inputs Adds to 310,320: Peak Hold View/Buy on Amazon