AC Current Switches and Sensors

Aim Dynamics is a well known current transformer supplier. We offer a wide variety of AC current sensors (also called current transformers or simply CTs).

To help you find what you’re looking for, we’ve broken down our products into six categories:

  • AC Amp Input -> AC 5 Amp Output    These "true" current transformers output up to 5 Amps AC at the rated current you select. These are all passive devices except for the 5A Rogowski coil kits, which require external power. This type of AC current sensor comes in various forms including solid an split core current transformer styles.
  • AC Amp Input -> AC 1 Amp Output   These current transformers output up to 1 Amp AC at the rated current you choose. These are all passive devices. This type of AC current sensor is offered in a couple styles including solid and split core current sensor styles.
  • ​​​​​​AC Amp Input -> 4-20mA  Output   These current sensors output a 20 mA signal at the rated current and 4 mA at zero. The split-core current sensors are passive but the 4-20 mA Rogowski coil kits require either an external power source, or 9-36 Vdc power from the 4-20 mA loop, depending on the model.
  • AC Amp Input -> DC Voltage Output   These current transducers output a DC voltage on the secondary corresponding to the current detected on the primary. These exist as both split-core and Rogowski coil kit options.
  • AC Current Switch   These AC current switches turn on an electronic switch (connecting the secondary wires) at the threshold AC current (detected on the primary conductor). The thresholds range from 0.015A to 5A, depending on the model.  Some thresholds are configurable on the unit itself.

Aim Dynamics carries AC current sensor devices from a range of manufacturers including:

    Things to consider when selecting AC current sensors:
    Input Rating
    & Output Signal

    There are two critical things to get right when ordering a current sensor:

    1 - The input rating.
    2 - The output type.

    Input Rating
    CTs have input ratings.  For example, the SCT-0750-100 has a 100A rating, and the manufacturer has specified that it will operate from 10% to 130% of the rated current with a specified accuracy.  IEC
    61869-2 states the accuracy from 5% to 120%.  Therefore, the SCT-0750-100 would be suitable for a circuit where the current doesn't drop below 10A often, and that doesn't exceed 130A.

    Output Type
    CTs can output AC current, AC voltage, DC voltage, 4-20mA signals, and more.  Therefore, it is critical to understand what input your measuring device (e.g. meter) expects.  Getting this wrong can result in device failure, incorrect results, and more.

    If you are unsure, contact your meter manufacturer to determine the input signal required.
    Solid-Core vs. Split-Core
    Solid-core current transformers offer a cost-effective and accurate solution for designing power meters dedicated to new equipment and buildings. They are not suitable, however, for the numerous applications involving power monitoring of existing machines and facilities, where it would be necessary to shut down power and disconnect cables before retrofitting the solid core sensors in all the places where they might be used. Installing power metering systems is generally not possible, prohibitively expensive or even dangerous if it requires a service interruption, even for a short while (e.g. stopping a production line, a telecom or datacenter power supply, some nuclear plant equipment, etc).

    Split-core current transformers can simply snap over a conductor, without the need to screw or weld on complex brackets, making installation and maintenance simple. They can be installed in electrical control panels – thus avoiding complex wiring – to remotely monitor devices that sometimes operate in inaccessible or harsh environments. The beauty of the split core transformers is that they can be retrofitted into a live installation without disturbing it, which often make them the unique choice for engineers designing power meters.

    But these advantages have a price, making the split core current transformers more expensive and less accurate than the solid core transformers. It is thus very important to understand the difference between the various technologies available, and make a choice according to specific application constraints.

    Core Material
    Ferrite vs. Nickel vs. Silicon Steel
    Current sensors can be manufactured with many different types of core materials.  The most commonly used materials are:

    Ferrite: The ferrite qualities are available at low cost, which puts high performance split core current transformers on the market at a very attractive price.  Ferrites are ceramic compounds of various transition metals with oxygen, which are ferrimagnetic but nonconductive.  Ferrite ceramics are a class of ceramic compounds made from iron oxide, and one or multiple metallic elements. The magnetic cores made from ferrite ceramics are used in high-frequency applications. The ceramic materials are produced in different specifications to meet diverse electrical requirements. These ceramic materials serve as efficient insulators, and help decrease eddy currents.

    ​​​​​​​Nickel: Nickel offers high accuracy ratings with low phase shifts, but it cannot tolerate high frequencies as well as ferrite, nor does it perform as well in over-current situations.  It is often used with low current measurement CTs.  This metal is glassy or non-crystalline, making it useful for high performance transformers due to low conductivity.

    Silicon Steel: Silicon steel has high electrical resistivity and long-term performance stability.  Silicon steel offers high saturation flux density. Silicon steel works well with CTs that have a higher current rating.
    Frequently Asked Questions
    Here are some of the FAQs we get asked about AC Current Sensors and Switches:
    How can I select the best size of sensor for my project?
    Current transformers come in many shapes and sizes. The size of the sensor increases with higher currents because these conductors use a thicker gauge of wire, or a busbar with a greater cross-section.  Generally speaking, the more current you need to measure, the larger the current transformer will be. 

    If two sizes of sensor can fit around the conductor you wish to monitor, it is generally better to use the smaller CT.  Doing so will save you money (larger CTs are usually more expensive) and the larger CTs won't offer increased accuracy, as a general rule.

    Do I need special care when installing a current transformer?
    Low voltage CTs are safer to install than those CTs with a current output.  If you are installing a 5A or 1A CT, you will need to either install the CTs on a "cold" line or use a terminal block to short the leads until they become part of the circuit.

    It is important to remember that current transformers are directional. When you look at a current transformer (or its spec sheet), there will be a label indicating which side should point toward the source/load of your conductor. If you install a current transformer backwards, your meter readings will be incorrect.
    How can I decide if a split-core sensor or Rogowski coil would be best for my project?
    Similar to a split core sensor, a Rogowski Coil can be opened for easy retrofit installation. Also because a coil rope is so thin, it will provide a much larger window to fit wires through and it’s extremely flexible. When you are working in tight spaces, it’s a lot easier to work with a Rogowski Coil than a rigid split core current transformer.

    It is also important to remember that a Rogowski Coil does have a greater cost so it will depend on what your budget is for the project and how much current you will be measuring.

    Lastly, if the meter you are using doesn't support Rogowski coils natively, you will need an integrator to use a Rogowksi coil, which implies higher cost and this requires active power.  In those situations you should use a Rogowski coil as plan B - only to be used in cases where traditional CTs won't fit.

    You may also want to watch this recent video of General Manager, Victor Fehlberg, discussing Magnelab's current transformers.
    What add-on items will I need when planning my power metering use of current sensors?
    If the CT or Rogowski coil solution you are purchasing requires active power, you should have the option to add a compatible power supply when adding the item to your shopping cart.

    Certain meters may require a special connector - we can often install those for you.  See if you meter's connector type is listed as an additional option when adding the product to your cart.

    Lastly, many CTs can be configured with a different lead length.  Ordering longer leads usually requires a longer lead time, but it may be more convenient in the end (as opposed to splicing in the field).