Donut Current Transformers RCT Series

The RCT Series Donut Current Transformers (CTs) are indoor-type, toroidal (ring-shaped) transformers designed for safe and accurate current measurement, power monitoring, and relay protection in low-voltage AC circuits. With a compact, lightweight design and easy panel-mounting, they are ideal for energy management systems, electrical panels, and industrial applications.

Key Features & Benefits

• Compact & Lightweight: Donut (toroidal) shape allows for easy installation around conductors without disconnecting them.
• Accurate Measurement: Provides precise current transformation for metering and monitoring applications.
• Wide Current Range: Available in multiple current ratios from 75/5A to 1800/5A to suit various load requirements.
• Low Power Consumption: Minimal burden (2.5VA to 10VA) ensures efficient operation without affecting circuit performance.
• Robust Construction: Designed for durability and long-term reliability in indoor environments.
• Easy Installation: Panel-mountable design simplifies integration into existing electrical systems.
• Customizable: Can be customized based on specific requirements for window size, current ratio, and accuracy class.

Technical Specifications

Operating & Installation Environment

• Installation: Indoor use only
• Ambient Temperature: -5°C to +40°C
• Relative Humidity: ≤ 60%
• Altitude: ≤ 2000m
• Atmospheric Conditions: No severe pollution, corrosive gases, or explosive hazards.

Applications

• Energy management and power monitoring systems
• Electrical submetering in commercial and industrial facilities
• Protective relay circuits in switchgear and control panels
• Integration with power analyzers, meters, and data loggers
• Load profiling and power quality analysis

How to Select the Right Donut CT?

Choosing the correct current transformer is crucial for accurate measurements. Consider these factors:

• Primary Current: Select a CT with a primary current rating equal to or higher than the maximum current in the circuit.
• Burden (VA): Ensure the CT's burden rating matches or exceeds the total burden of connected meters and relays.
• Accuracy Class: For billing or precision measurement, choose Class 1 or better. For protection, Class 5P or 10P may be suitable.
• Window Size: The conductor must pass through the CT's central opening. Measure the cable or bus bar diameter to ensure a proper fit.

Installation Guidelines

• Ensure the power is off before installation, or use insulated tools for live-line mounting (if designed for it).
• Mount the CT securely on a panel or DIN rail, keeping it away from strong magnetic fields or heat sources.
• Pass the primary conductor through the center of the donut hole. For best accuracy, center the conductor and avoid bending it near the CT.
• Connect the secondary terminals to the measurement or protection device using appropriate gauge wires. Never open-circuit the secondary while the primary is energized.
• For safety, always ground the CT's metal case (if applicable) according to local electrical codes.

Ordering Information

When ordering, please specify:

• Model (e.g., RCT-GS or RCT-GI)
• Current ratio (e.g., 100/5A)
• Accuracy class (e.g., Class 1)
• Window aperture size (if custom)
• Any special requirements (custom labeling, lead length, etc.)

Frequently Asked Questions (FAQ)

What is the difference between ring CT and wound CT?

A ring CT (donut CT) has a toroidal core with a hole for the conductor to pass through. It's non-invasive and easy to install. A wound CT has primary windings physically wrapped around the core, offering higher accuracy but requiring circuit disconnection for installation.

Is there a DC current transformer?

Yes, DC current transformers exist but use different technologies (like Hall-effect sensors or fluxgate sensors) because traditional CTs only work with AC currents. They measure DC by converting it to a proportional AC signal or using magnetic modulation.

What is the difference between CTs and VTs?

Current Transformers (CTs) step down high current to a safe, measurable level (e.g., 5A). Voltage Transformers (VTs) step down high voltage to a safe, measurable level (e.g., 110V). Both isolate measurement devices from high-energy circuits.

What is the working principle of DC CT?

DC CTs typically use a magnetic core with a Hall-effect sensor. The DC current creates a magnetic field, which the Hall sensor detects and converts into a proportional voltage signal. This allows accurate DC measurement without physical contact.