FLEX-CORE® maintains a large in-stock inventory of Current Transformers to meet your needs.

Discover our range of 1-5A and 0.333-1V current transformers to find the perfect fit for your specific application. Our inventory includes Split-Core, Solid-Core, Low Voltage, Medium Voltage, Clamp-On, and Rogowski Coils tailored for various common applications.

For pricing and availability on one of our current transformers, please contact us at (614) 889-6152 or request a quote. Alternatively, you can engage in a live chat conversation with one of our knowledgeable sales representatives; simply click on the live chat tool located in the lower right corner of any page.

We offer same-day shipping for most current transformers when orders are placed before 1:00 PM Eastern time, ensuring prompt delivery for your requirements.

  • Wire Size Calculator

    The Flex-Core Wire Size Calculator is used to determine the proper gauge of wire for your application.

  • CT Burden Chart

    Use our CT Burden Chart to help select the appropriate current transformer to ensure your CT can handle the load without exceeding its accuracy limit.

  • How to Wire a Current Transformer

    Learn how to properly wire your current transformer to your power source and meter.

Find Your Current Transformers by Type

FCL-Split-Core Current Transformer

Split-Core Current Transformers

Designed for easy installation over existing bus or wire conductors without interrupting the circuit.

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2RL Solid-Core Current Transformers


The preferred choice for new installations when there is no concern of disrupting the circuit.

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615 Split-Core Current Transformers

Low Voltage

Rated for applications requiring a primary current up to 600V (ANSI/IEEE) or 720V (IEC).

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CTWH3-60-T50 Solid-Core Medium Voltage Current Transformer

Medium Voltage

Rated for applications requiring a primary current ranging from 600V up to 34.5KV.

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143-Solid-Core Zero Sequence Current Transformer

Zero Sequence

Zero sequence current is monitored using a core balance approach, where all three phases of a three-phase system are passed through a single current transformer.

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RCT-1800 Rogowski Coil CT

Rogowski Coils

Less power loss compared to traditional CTs, provides greater energy savings, and reduces lifecycle costs.

View all Rogowski Coil models >>

Clamp-On Current Transformers

Designed for single-handed operation and typically used for short-term energy readings.

View all clamp-on models >>

Current Transformers - Frequently Asked Questions

Current transformers are an electrical device that safely and accurately measures electrical current in power systems and circuits. It operates on the principle of electromagnetic induction, reducing high primary currents to proportional, lower secondary currents. CTs provide:

  • Electrical isolation between the primary (high-current) and secondary (low-current) circuits.
  • Making them essential for tasks like metering energy consumption.
  • Protective relaying.
  • Monitoring current in industrial processes.

They ensure equipment and personnel safety while delivering precise current measurements, serving as a fundamental tool in electrical engineering and power distribution.

Current Transformers work based on the principle of electromagnetic induction. Current transformers consist of a primary winding, typically a single turn or a few turns of a conductor, and a secondary winding, with many more turns, wound around a magnetic core.

When an alternating current (AC) flows through the primary winding, it generates a magnetic field in the core. This magnetic field induces a proportional voltage in the secondary winding, which can be measured using instruments or protective relays. The fundamental principle is that the CT steps down the current, making it safe and convenient to measure while maintaining a proportional relationship between the primary and secondary currents, allowing for precise current measurements and protective actions in electrical systems.

No, standard current transformers (CTs) designed for measuring alternating current (AC) cannot be used for direct current (DC) measurements. CTs operate based on the principle of electromagnetic induction, which relies on the changing magnetic field produced by AC currents to induce voltage in the secondary winding. In contrast, DC currents generate a constant magnetic field that does not change in direction or magnitude. As a result, a standard AC CT cannot accurately measure DC currents since there is no changing magnetic field to induce voltage in the secondary winding. To measure DC currents accurately, specialized DC current transducers (DCCTs) are used, designed with different core materials and construction to work effectively with constant DC currents.

In a current transformer (CT), the primary current flows through the primary circuit, typically a conductor or power line passed through the CT's core. The primary current is the current that needs to be measured or monitored. CTs are designed to step down this primary current to a proportional, reduced secondary current. The secondary current is the output of the CT, and its magnitude is directly proportional to the primary current, as determined by the CT's transformation ratio. This step-down process ensures that the secondary current is safe and manageable for measurement or use in various applications, such as metering, protective relaying, and control systems.

The specific choice of current transformers depends on the application's requirements, including current magnitude, accuracy, installation constraints, and environmental conditions. Selecting the correct type of CT is crucial to ensure accurate, current measurement and protection in electrical systems.

  1. Wound Current Transformers: These are the most common type of CTs. They consist of a primary winding, a secondary winding, and a magnetic core. The primary winding is connected in series with the circuit carrying the primary current to be measured. Wound Current Transformers are versatile and widely used in various applications, including metering and protective relaying.
  2. Bar-Type Current Transformers: Bar-type CTs consist of a solid metal bar, usually made of copper or aluminum, with a secondary winding wrapped around it. They are often used in high-current applications and are known for their robust construction and reliability.
  3. Bushings or Window-Type Current Transformers: These CTs are designed to be installed on high-voltage equipment, such as transformers and circuit breakers. They have a hole or window through which the primary conductor is passed. This design makes them suitable for retrofitting existing equipment without interrupting power flow.
  4. Resin-Cast Current Transformers: Resin-cast CTs have their windings encapsulated in epoxy resin, protecting against environmental factors like moisture and dust. They are commonly used in outdoor and high-voltage applications where durability and reliability are crucial.
  5. Low-VA (Volt-Ampere) CTs: These current transformers are designed for applications where a low burden (connected load) is required, such as protection relays. They have a high turn ratio to provide a small secondary current, reducing the burden on the measuring device.
  6. Split-Core Current Transformers: Split-core current transformers have a hinged design, allowing them to be easily installed around existing conductors without disconnecting the circuit. They are commonly used in retrofit and maintenance applications.
  7. Zero-Sequence Current Transformers: Also known as ground CTs, these are used to measure zero-sequence currents in three-phase power systems. They are crucial for ground fault protection and detecting imbalances in the system.
  8. Summation CTs: These CTs are used to sum the currents from multiple primary conductors into a single secondary winding. They are often used in applications where the total current of several parallel conductors needs to be measured accurately.
  9. Protection CTs: Designed for protecting relaying applications, where fast and precise detection of overcurrent and fault conditions is essential. These current transformers meet strict accuracy and performance standards.
  10. High-Frequency Current Transformers: Designed to accurately measure high-frequency currents, often encountered in power electronics and high-frequency applications.