Non-Invasive Current Sensor - 30A

Replacement:SEN-11005. We are now carrying a current transformer from a different supplier. This page is for reference only.

This current clamp can be used to detect a current of up to 30A. Simply clip it around the current source that you wish to measure and it will produce a (very) small AC voltage proportional to the current. The cable is terminated on one end with a standard 3.5mm jack (like a headphone jack).

Use this to build your own energy monitor and keep your power usage down, or use it to to build an over-current protection device for an AC load. See the link below for an example project. Check out the datasheet for the pinout of the 3.5mm jack


Looking for answers to technical questions?

We welcome your comments and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.

  • There are 1800 turns on the coil inside. Just FYI.

  • n1ist / about 13 years ago / 2

    The last picture shows how a gfci works. It will measure the imbalance between hot and neutral (which is assumed to be leaking somewhere due to a fault)

  • Rude / about 13 years ago / 1

    I've checked the PDF, but for the life of me I cant determine how many turns are on this CT, or what the load resistor is that is built into it.
    Does anyone have any specific information about this 30A CT?

    • Rude / about 13 years ago / 1

      it looks like there are two resistors in there - one 24ohm, the other 29ohm in series.
      Anyone have any idea of how to estimate the number of turns on the transformer inside? :)

  • makeder / about 13 years ago / 1

    hi, i was looking at the example project and it seems they use a different sensor and use a dc jack to connect the current sensor to the board, is there a jack that works with this one? or can you just connect the output to positive?

  • Member #92825 / about 13 years ago / 1

    been over a month and a half since I order this...........

  • adrianTNT / about 13 years ago / 1

    Anyone knows if these can be used to monitor current going through car spark plugs?

    • irab88 / about 13 years ago / 1

      Probably not, as spark plugs pulse extremely fast with micro-amperes of current. You would need to have a very sensitive and accurate piece of equipment for that.

  • JayK / about 13 years ago / 1

    For an idea of what you can do with a current transformer, check out It's an open-source energy meter my buddy and I made.

  • pubdc / about 13 years ago / 1

    Great product, against all those asking for a higher rated version, can I ask for a smaller one : I would like to measure individual circuits (areas, appliances, lights) in the house. something like 2 amp, 5 amp, and 10 amp would be cool. Sign me up for 30pcs in total in that case.

  • Ted M / about 13 years ago / 1

    Regrettably, from past experience, this type of device isn't as simple as clamping it around your extension cord and reading the current. I believe you still have to remove one of the two wires in the extension cord. Oh, and it only works for AC.

    • PresidentOfAwesomeness / about 13 years ago / 1

      Yeah, but these should work with pulsed DC, too.
      It looks pretty interesting... I might want to get one of these myself.

    • Rawdust / about 13 years ago / 1

      That is correct. The first post points out an error in the photo. n1ist says you can use it on the whole cord for GFCI. I would not trust that set up for GFCI.

  • WetDogNose / about 13 years ago / 1

    When I saw this I thought "Ace I have been waiting for ages to replace the hacked whole house monitor I currently have" then I saw it is only for up to 30 amps! Any chance you can source a higher rated sensor with a similar setup to cover a whole house?

  • Rawdust / about 13 years ago / 1

    The data sheet says the output is Voltage/1V. I believe something got lost in translation. The CT clamps I've seen usually have the output be something like 1mv/A or 10mv/A.
    Also the example uses a burden resistor to get a voltage. The resistor is built into this sensor.

    • trl / about 13 years ago / 1

      Yeah, i questioned that too. Now i understand that Voltage/1V means that it is a voltage mode unit (has built-in current sense resistor to convert current into voltage) and 1V means that the full scale current of 30A would read 1V (apparently the burden resistor is 1v/30a = 33.33333333 milli-ohms). Could measure quite accurately using Vref = 1v with 10-bit ADC in the Arduino.

  • doobie / about 13 years ago / 1

    Any chances that the 100amp one will be available?

    • We can check into it. We'll have to see how popular this one is.

      • RVaughan2 / about 13 years ago / 1

        I would grab 2 right off the bat if you stocked the 100Amp sensors. Seeeduino has the 100Amps for a good price, I would just rather purchase from someone a little more 'local' and not have to worry about long shipping delays, lost orders or what have you.
        I have a feeling you'd run out of stock real quick. How about a pre-order/request submission for them to let us show you just how much we'd like to see you stock them :)

  • khearn / about 13 years ago / 1

    You might want to mention that this will only work for AC current.

  • doobie / about 13 years ago / 1

    Any idea what happens if I run this on a wire with > 30a? Will it burn out or just return 30a?

    • noworries / about 13 years ago / 1

      Two things may happen. The most likely is that the inductor will saturate and the output would indicate slightly higher than 30A, even with significant increases in the actual current flowing through the device.
      The second thing that could happen is that the shunt resistor inside the sensor could fail since it could be operated outside of its design parameters. If it should fail open, depending on the impedance of the circuit it is connected to a dangerous voltage potential may exist across the coil output.
      It is a very good idea to use these devices with this potential failure mode in mind, and to not exceed their current sensing limits.

  • 77521 / about 13 years ago / 1

    Nice product and reference to impressive project based on Atmel 465 code.
    How would a breakout board with an Atmel 465 (or a more recent verson of it) compare cost-wise to using an Arduino?
    How about a breakout board with a true RMS chip on it, such as an AD636, AD736 or BB4341?

    • Member #30843 / about 13 years ago / 1

      I have an in-progress project using this sensor with a LTC1966 true RMS chip. It should be a lot easier to build a multichannel current monitor if you can sample DC out the the true RMS chip rather than an AC waveform.
      I too would like lower current versions of the sensors.

  • Member #1340 / about 13 years ago / 1

    Nit pick warning!
    The last picture shows the hot and neutral lines passing through the hole in the sensor. The sensor will not be able to read the load current if both sides of the load are passed through the hole. Only the hot or the neutral should be passed through the hole to read the load current. In this configuration you would only see the ground current, hopefully there would be none to see.
    Nit pick off, thanks

    • You'd have worse problems than that if you try to pass 30A through those little bitty wires. Normally you'd clamp this puppy around a rather large conductor to measure the current going through it (that's why the hole is so big). If you want to measure the current going into your house, you could use a couple of CR3110's (75A) or CR3111's (100A) that are available from

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