Troubleshoot ground loops with clamp multimeter

A normal way to troubleshoot ground loops problems in audio systems is to listen to the audio signal at the mixer with headphones. If the buzz exists at the mixer then do the following: One by one, disconnect the inputs and outputs to and from the mixer and note if the buzz decreases. This same connecting and disconnecting wires method can be used on other components of audio and video systems.

Disconnecting and then reconnecting the cables take a lot of work. This caused that ground loops are frustrating to troubleshoot in large systems where there are lots of cables.

I have found that a clamp type multimeter can help to troubleshoot ground loop problems. The ground loop noise is normally caused by the extra noise current flowing on the shields and ground wires of the cables. That noise current is normally mains voltage frequency (50 Hz / 60Hz) or it’s harmonics. Normally the signal cables should not carry any (or very little) mains frequency current in them, so by measuring this kind of current flowing on the cable it is possible to determine where the noise current flows. A clamp type multimeter is a very good tool for doing the measurements, because you can easily measure the noise current flowing on the cable with it without need to disconnect the cable or disturb the signal inside the cable. This means that you can troubleshoot a live system with clamp multimeter in AC range.

The wires which have considerable current on them are part of ground loop. The wires with most current on them are pushing most noise current to the whole system. So first locate the wires that have highest or otherwise very high current flowing in them. Then you can try to disconnect them and test if that stops the noise. Usually there is one or few cables that cause all or most ground loop current on the system. That noise current gets typically flowing around in different cables on the system, causing more or less noise problem here and there around the system. Then the real noise source or sources are disconnected, suddenly the whole system becomes noise free. When you have found out the problem source then just add suitable cure to that connection (typically signal isolation transformer or similar device).

Clamp on multimeter allows you to easily measure the current on cables. Just clamp the meter over the audio cable and get the AC current reading. If you want you can clamp several audio/video cables inside the clamp and get the reading of the sum of their noise currents (remember that there is possibility that if there are two cables with exactly same noise signal but different direction you get zero reading). Clamping the meter around a number of signal cables speeds up the troubleshooting process where there are lots of cables, for example near audio mixer. If the group of cables you measured with clamp meter shows a considerable noise current, then measure the cables individually to see which one has the most current flowing. If there was no considerable current on the cable group, continue measuring next cable group. Besides audio cables you can do the measurement with video cables, mains power cables and other signal cables.

There are few things to consider the selection of the clamp type multimeter. First the multimeter needs to measure the AC currents with the clamp. You don’t need the DC current measuring capability, although getting a clamp meter with also DC capability can make the meter more useful for other applications (usually the DC capable clamp meters are more expensive than AC only). The second thing to consider is the resolution of the meter. The ground loop currents you normally want to measure are in few mA to 1A range (in some severe case the current can be considerably more). It is preferred to have a clamp meter that can measure currents down to few mA. Unfortunately many meters with this good resolution are usually quite expensive.

Usually the cheap clamp type multimeters have 10 mA or 100 mA resolution, meaning that they can’t detect anything lower than 10 mA or 100 mA. A multimeter with 100 mA resolution is practically useless in ground loop problem solving, because over 100 mA ground loop current are not seen often. A multimeter with 10 mA resolution is already useful to troubleshoot ground loop problems, but it will not reveal you all the details in most cases. Usually 100 mA-1A current on cable means very serious noise problem on audio and video systems, currents in 10-100 mA range cause some noise problems. Usually when the current is well below 10 mA there are no considerable noise problems.

I have used a clamp meter with 10 mA successfully for troubleshooting ground loop problems, but when used that I wished I had a meter that can show even lower currents down to 1 mA or less. So if you are buying a clamp meter, consider trying to get as good resolution as possible with the money you are willing to spend it. When looking for multimeter for this application the actual measuring accuracy (measurement error percents promised) is not important, we are merely making checks if there is current flowing or not and approximately how much (just some approximation around how much current is enough).


This picture shows the cheapest I know well working clamp multimeter that can measure currents AC down to few mA currents. The meter has 1 mA resolution at 2A measurement range (the display started showing current higher than 2 mA). You can get this 1.3″ LCD Clamp Style Digital Multimeter with Pouch from Dealextreme for around 20 US dollars.


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  26. Tomi Engdahl says:

    Leakage-current clamps reduce downtime

    The Fluke 368 FC and 369 FC leakage-current clamps help technicians identify, document, record, and compare readings over time to prevent problems before they happen. These rugged meters have large diameter jaws—40 mm for the 368 FC and 61 mm for the 369 FC—and capture leakage-current signals as low as 10 µA. The clamp’s jaw is fully shielded to minimize external electromagnetic interference.

    Fluke 368 FC Leakage Current Clamp Meter

    The Fluke 368 FC true-rms leakage current clamp meter helps you measure small problems before they become large problems, all without taking equipment off line.

  27. Tomi Engdahl says:

    Measuring ground loop resistance without stakes

    Normal earth ground measurement involves disconnecting parallel grounding rods, “planting” several auxiliary grounding stakes, and using a earth ground tester to calculate the resistance of grounding system electrodes. Sometimes, though, there isn’t anywhere to plant the grounding stakes—such as inside a building, at a cell phone substation, or on power pylons. What then?

    With the Stakeless testing method, earth ground stakes aren’t necessary. Place an earth ground clamp like the Fluke 1630 around the earth ground rod or the connecting cable. One half of the clamp will induce a known voltage while the other half measures current. The tester automatically determines the ground loop resistance at this grounding connection. You can also conduct continuity testing, leakage current measurement, and lighting protection system inspections much the same way, also without breaking the circuit.

    The Fluke 1630 measures ground resistance from 0.025 to 1500 ohms and true-rms current flow from 0.02 to 35 A

  28. Tomi Engdahl says:

    Is NOISE getting to you?

    Don’t let it slow you down. The Megger DET14C/24C clamp-on ground testers help identify noise problems that CATV companies have when introducing DOCSIS3.1. Let us show you how to use the unit to mitigate noise troubles caused by increased bandwidth.

    DET14C and DET24C Digital Earth Clamps

    Elliptical clamp shape improves access to earth cables and straps up to 50 mm

    ■Low maintenance flat jaw interface
    ■Measures ground resistance from 0.05 Ω to 1500 Ω
    ■Measures true RMS ground leakage current from 0.5 mA rms to 35 A rms
    ■CAT IV 600 V safety rating
    ■Backlit LCD display

    The earth resistance clamp meters are particularly suitable for
    measuring earth resistance in various installations such as buildings,
    pylons and RF transmitter sites without system disconnection. In
    addition, they can be used for the inspection and verification of
    lightning protection systems and virtually any installation where a
    current loop can be generated

  29. Tomi Engdahl says:

    DET24C clamp-on ground tester

    Megger’s DET24C clamp-on ground tester helps identify noise problems that CATV companies have when introducing DOCSIS3.1.

    • It allows easy measurement of grounds.

    • It can measure the resistance of each “loop” to
    determine the degreeto which they’re balanced.

    • It measures resistance down to 1/100 of an Ohm,
    making it possible tomeasure the balance of the
    loops very precisely.

    Clamp-on Ground Resistance Testers

  30. Tomi Engdahl says:

    New Earth Ground Clamp measures ground loop resistance without stakes

    Fluke 1630 Earth Ground Clamp, a rugged clamp meter with a wide 35 mm jaw opening that offers time-saving ‘stakeless’ earth ground loop resistance and non-intrusive ground leakage current measurement for electrical contractors, field service, industrial maintenance and utility technicians.

    The new Fluke 1630 measures ground resistance from 0.025ohms to 1500ohms and leakage current from 0.2mA to 1000mA

    The Fluke 1630 Earth Ground Clamp is placed around the earth ground rod or the connecting cable. A known voltage is induced by one half of the clamp and the current is measured by the other half. The tester automatically determines the ground loop resistance at this grounding connection.

  31. Tomi Engdahl says:

    Clamp Meter Teardown (Voltcraft VC-330 = UNI-T UT210E)

    a teardown of my new Voltcraft VC-330 clamp meter. It turned out to be UNI-T UT210E with just a different brand name on it and a different color! I reverse engineered the schematic of the input section of it with the protections. It seems to be a nice clamp meter

  32. Tomi Engdahl says:

    Finding The Source of Stray Current on Grounding System

    Tracking down stray voltage in an electrical system can be a challenge! Here we go through the process of trying to find a faulty device, circuit, or appliance that may be malfunctioning and causing a partial fault or leak to the earth grounding system. I demonstrate the usage of a clamp style ammeter and by using the process of elimination we are able to find the source of the stray voltage and or current that was leaking into the grounding electrode system.

  33. Tomi Engdahl says:

    Finding The Source of Stray Current on Grounding System

  34. Marian says:

    Thank you for a useful information. This blog is what I am looking for. I’m using Fluke clamp multimeter. I’ll take note all of this information. If someone looking for a Fluke brand, please kindly check this link:

  35. Tomi Engdahl says:

    Another type of clamp meter that gives information on ground loops:

    Fluke 1630 Earth Ground Clamp Meter

    Dock Lifeguard – Checking Ground Rod Impedance

    Video showing how to test the impedance of the ground rod that is bonded to the dock. NEC states it should be 25 Ohms or less.

  36. Tomi Engdahl says:


    stake-less method for earth resistance measurement.

    Amazing. First clamper that i ever seen to measure the resistance.

  37. Tomi Engdahl says:

    Ground Rod Resistance

    The ground rod is an effective grounding component if used properly. Watch this video to learn more.

    Ground Resistance Measurement 250.53(A)(2) (26min:27sec)

    This real world test will be conducted by Nationally recognized Code Expert Mike Holt and electrical utility professional Joe Symmes using a 3 pole fault potential method, a clamp on meter to check the ground, an Amp meter to measure the current flow in the event of a ground fault and a volt meter and also test the test potential.

    Mike is nationally recognized as one of America’s most knowledgeable Code Experts and electrical trainers.

  38. Tomi Engdahl says:

    Measure loop leakage current and resistance at the same time:

    FR2000C+ 0.01Ω-1200Ω Clamp Ground Resistance Tester Loop Resistance Tester 0.00mA-20A Leakage Current Test 300 Sets of Data Storage


    Model: FR2000C+
    Resistance range: 0.01Ω-1200Ω
    Type: Multifunctional
    Resistance resolution: 0.001Ω
    Current range: 0.00mA-20A
    Current resolution: 0.01mA

    FR2000A+ Clamp Ground Resistance Tester 0.01Ω-200Ω Loop Resistance Tester 300 Sets of Data Storage

    ★Resistance range: 0-1200Ω
    ★Current range: 0-20A
    ★New black screen design, high-end luxury
    ★Ω + A same screen display
    ★Quick self-check function, no need to wait
    ★Using fast filtering technology, strong anti-interference ability
    ★New design, long life of clamp head
    ★300 groups of storage


    Model: FR2000A+
    Resistance range: 0.01Ω-200Ω
    Type: Practical
    Resistance resolution: 0.001Ω
    Current range: none
    Current resolution: none

    Function: ground resistance test, loop resistance test, leakage current test
    Accuracy: Ground resistance accuracy: ±1%±0.01Ω, current accuracy: ±2%±1mA

  39. Tomi Engdahl says:

    The basic principle of the ground resistance measurement of the
    clamp-type grounding resistance meter is to measure the
    loop resistance. See below. The jaw section of the clamp
    meter consists of a voltage coil and a current coil. The
    voltage coil provides the excitation signal and induces a
    potential V on the circuit under test. Under the action of the
    potential V, a current I will be generated in the circuit under
    test. The clamp meter measures V and I and uses the
    following formula to obtain the measured resistance R.

  40. Tomi Engdahl says:

    Clamp Ground Resistance Tester (Multifunctional)
    ★ Resistance Range: 0.01Ω-1200Ω
    ★ Current Range: 0.00mA-20.0A
    ★ New black screen design, luxury
    ★ Ω+A same screen display
    ★ Real-time clock function

    User manual

  41. Tomi Engdahl says:

    Energy and Power / Testing and Commissioning
    The easiest way to measure ground resistance using clamp meter, but be carefull!
    By Edvard

    The ground clamp meter / tester is an effective and time-saving tool when used correctly because the user does not have to disconnect the ground system to make a measurement or place probes in the ground.

    The clamp method requires a to measure. The operator has no probes and therefore cannot set up the desired test circuit. The operator must be certain that earth is included in the return loop. The clamp tester measures the complete resistance of the path (loop) that the signal is taking. All elements of the loop are measured in series.

    The method assumes that only the resistance of the ground electrode under test contributes significantly. Based on the math behind the method (to be reviewed below), the more returns, the smaller the contribution of extraneous elements to the reading and, therefore, the greater the accuracy.

    In addition, it includes the bonding and overall connection resistance. Good grounding must be complemented by “”, having a continuous low-impedance path to ground. Fall of potential measures only the ground electrode, not the bonding (leads must be shifted to make a bonding test).

    Because the clamp uses the grounding conductor as part of the return, an “open” or high resistance bond will show up in the reading.

    The clamp ground tester also allows the operator to measure the leakage current flowing through the system. If an electrode has to be disconnected, the instrument will show whether current is flowing to indicate whether it is safe to proceed.

    Unfortunately, the clamp ground tester is often misused in applications where it will not give an effective reading. The clamp method is effective only in situations where there are multiple grounds in parallel. It cannot be used on isolated grounds as there is no return path.

    Unlike with , there is no way of proofing the result, meaning the results must be taken on “faith.” The clamp ground tester does fill a role as one tool that the technician could have in his “bag”, but not the only tool.

    The head of a clamp ground tester includes two cores (see figure 5). One core induces a test current and the other measures how much was induced. The input or primary voltage of the test current inducing core is kept constant, so the current actually induced into the test circuit is directly proportional to the loop resistance.

    The important thing to remember with clamp testing is that clamp ground testers effectively make loop resistance measurements. Clamp measurements are loop measurements. For the clamp method to work there must be a series- parallel resistance path (and the lower the better).

    The measurement of the loop resistance is relatively close to the resistance of the ground electrode being tested.

    In summary, remember that a clamp ground tester measurement is a measurement of the resistance of the entire loop. There must be a loop resistance to measure. If there isn’t a loop to measure the operator can create one with a temporary jumper lead. The greater the number of parallel paths, the closer the measured value will be to the actual earth resistance of the electrode under test.

    Remember that the earth path must be in the circuit to measure ground resistance. This caveat sounds obvious, but if you have metal structures involved there may be a connection through that, rather than the earth mass.

  42. Tomi Engdahl says:

    Review and Teardown of a Kaiweets HT208D Inrush Clamp Meter

    In this video, I did a review and teardown of a Kaiweets HT208D 6000 counts inrush clamp meter. Despite some minor annoyances, the overall quality of the meter is in general quite good.

  43. Tomi Engdahl says:

    Cheap earth leakage meter review video

  44. tomi says:

    Maybe some day I open a twitter account.
    The constant hacking problems on twitter has made me to wonder would using that service be good at all…

  45. tomi says:

    You can’t download this theme anywhere. It is custom made for this site.

  46. tomi says:

    You are using similar design on your site, but not exactly the same.
    The blog on this site used to run earlier a bit slowly, but moving the site to more powerful server did wonders.
    Earlier the poor MySQL performance was the slowing factor, now the database server is powerful enough so things run smoothly.


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