Current Transformers (CT) | Current Measurement for Metering & Protection

What Are Current Transformers (CT)?

Current Transformers (CT) are instrument transformers designed to reduce high primary current to a safe, measurable secondary current for meters, protective relays, and monitoring equipment. By providing accurate current representation and electrical isolation, CTs enable safe system diagnostics and protection without directly connecting sensitive devices to energized conductors.

How Are Current Transformers Used?

CTs deliver a scaled current signal to instrumentation and control systems, supporting real-time monitoring and automated protection. They are commonly installed on feeders, mains, and branch circuits to help operators measure load, verify performance, and detect fault conditions quickly and accurately.

Common Applications

Utility and industrial substations
Metal-clad and metal-enclosed switchgear
Medium-voltage and low-voltage distribution systems
Protective relaying and fault detection
Energy monitoring and power metering
SCADA and facility power monitoring systems
Critical facilities and data center infrastructure

Types of Current Transformers

Type	Description	Typical Use
Solid-Core CT	Fixed core design offering high accuracy and stability	New installs and switchgear integration
Split-Core CT	Hinged core design for install without disconnecting conductors	Retrofits and upgrades
Window / Donut CT	Conductor passes through CT window for measurement	Switchgear and feeder monitoring
Bar-Type CT	Integrated primary bar for compact installation	Panelboards and high-current systems

Key Specifications to Consider

CT Ratio: Primary-to-secondary current ratio (example: 600:5 or 2000:5)
Secondary Rating: Common secondary outputs are 5A or 1A
Accuracy Class: Select metering class or protection class based on application
Burden Rating: Load the CT can support without accuracy loss
Thermal & Short-Time Rating: Withstand capability under fault conditions
Mounting & Window Size: Ensure fit for conductor size and installation environment

Why Current Transformers Matter

Accurate current measurement is essential for load monitoring, energy management, and fault protection. CTs supply critical current signals to protective relays for overcurrent detection, ground fault monitoring, and system coordination. Proper selection helps prevent nuisance trips, supports selective coordination, and strengthens the reliability of distribution systems.

Why Choose Larson Electronics?

Larson Electronics supplies current transformers selected for accuracy, durability, and long-term reliability in demanding power environments. Our CT solutions support utility, industrial, and mission-critical applications where dependable current measurement and protection are essential. Backed by responsive technical support and fast quoting, Larson Electronics helps customers maintain safe, efficient, and well-monitored electrical systems.

For more information or assistance selecting the right current transformer for your application, contact Larson Electronics. Larson Electronics – Building Trust Since 1973.