Split Core Current Transformer: How It Works, Key Specs & Installation Guide

What Is a Split Core Current Transformer?

A split core current transformer (also called a split-core CT, clamp-on CT or hinged current transformer) is a current transformer whose magnetic core can be opened and closed around a conductor, so it can be installed without disconnecting the cable or de-energizing the circuit. It is the preferred solution for retrofitting current monitoring, metering and protection to existing switchboards, feeders and machines where interrupting the supply is not acceptable.

How Does a Split Core Current Transformer Work?

Like a solid core CT, a split core CT works by electromagnetic induction: the primary conductor passes through the window, and the alternating current it carries creates an alternating flux in the core, which induces a proportional current in the secondary winding. The difference is mechanical — the core is manufactured in two halves, one fixed and one hinged or removable. When the two halves are closed around the conductor, the magnetic circuit is completed and the CT operates exactly like a solid-core unit.

Because the core has a physical air gap at the joint, the magnetizing current is slightly higher and the accuracy is generally a little lower than an equivalent solid-core CT of the same class. Modern CNC-machined mating surfaces keep this gap effect small, and high-permeability cores such as silicon steel or nanocrystalline material maintain good accuracy in the class 0.5 to 1 range.

Key Parameters of a Split Core Current Transformer

Accuracy class: typically class 0.5, 1 or 3 — class 0.5 suits energy metering, class 1 and 3 suit monitoring and protection.
Rated primary current and transformation ratio: e.g. 100/5 A, 250/5 A or 600/1 A, with the ratio defined by the secondary output needed.
Secondary output: commonly 5 A, 1 A or mV-level voltage output for electronic meters and data loggers.
Window / bore size: the diameter or dimensions of the opening, which must clear the cable plus insulation and bending radius.
Rated frequency and insulation level: 50/60 Hz standard; working voltage and insulation class must match the installation.
Mechanical design: hinge type, clamp mechanism, gasket sealing (for outdoor use) and mounting bracket options.

Split Core vs. Solid Core Current Transformer

A solid core CT is more accurate and lower cost, but it must be slipped over a conductor before the cable is terminated — which means installing it only during new construction or a planned outage. A split core CT trades a small amount of accuracy for the ability to clamp around a live conductor in minutes, which is why it dominates retrofit applications: energy management retrofits, panel upgrades, feeder monitoring and temporary surveys. For metering-grade billing accuracy, specify a split core CT with an appropriate class and verify linearity over the expected load range.

How to Choose the Right Split Core Current Transformer

Measure the conductor and clearance — the window must fit the cable, its insulation and any protective sleeve with room to spare.
Define the measurement purpose — billing and energy management need class 0.5; simple monitoring and overload detection can use class 1 or 3.
Select the ratio and output — match the full-load current and the input range of the meter, relay or logger (5 A, 1 A or mV).
Check the installation environment — indoor or outdoor, temperature range, humidity and whether a sealed or gasketed body is required.
Verify secondary burden — the CT must drive the connected burden (wire resistance plus instrument input impedance) without exceeding its rated output.

Applications of Split Core Current Transformers

Energy monitoring and submetering retrofits in commercial buildings and factories
Feeder and branch circuit monitoring in existing switchboards
Motor load and current monitoring without production stoppage
Smart meter and IoT power measurement installations
Photovoltaic and energy storage system monitoring
Temporary load surveys and power quality studies

Shaanxi SiRui Technology Co., Ltd Split Core Current Transformer Range

Shaanxi SiRui Technology Co., Ltd supplies split core current transformers for retrofit metering and monitoring, available in multiple window sizes, ratios and accuracy classes with flexible secondary outputs, hinges and sealing options, plus full OEM/ODM customization. Products are manufactured under ISO 9001:2015 with RoHS and REACH compliance.

FAQ

Can a split core CT be installed on a live cable?

Yes — that is the main advantage of a split core design. The core opens and clamps around the conductor without breaking the circuit. However, local safety rules, working at height and personal protective equipment still apply, and the secondary winding must never be left open while the primary is energized.

Is a split core CT as accurate as a solid core CT?

Close, but not identical. The removable joint introduces a small air gap that raises magnetizing current, so a split core CT is normally specified at class 0.5 to 1 rather than the 0.2 to 0.5 class achievable with high-grade solid core designs. For most monitoring and sub-metering applications this is fully sufficient.

Why must the secondary of a CT never be opened under load?

An open secondary removes the load that opposes the primary flux, so the core saturates and a very high voltage can appear across the secondary terminals, damaging insulation and endangering operators. Always short-circuit the secondary before disconnecting instruments.

Talk to Our Engineers

Need help selecting a split core current transformer for your retrofit project? Contact Shaanxi SiRui Technology Co., Ltd — our engineers will recommend the right part, provide samples and share detailed datasheets.