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Standard Current Transformers
Standard and custom toroidal current-sensing (instrument) transformers for accurate measurement and protection.
Toroidal Current-Sensing Transformers (CTs)
Since 1982, Bridgeport Magnetics has designed and manufactured high-precision toroidal current-sensing transformers for accurate current measurement in power lines and bus bars. These compact instrument transformers deliver excellent linearity, low VA burden, and reliable performance in space-constrained environments, with options for voltage-generating configurations used in electronic power monitoring systems.
Our toroidal CTs are available in both standard and fully custom designs. They can be supplied with protective insulation via taping, resin dipping, or epoxy potting, and are also offered fully cast and encapsulated in epoxy as individual units or multi-phase assemblies. Voltage-generating types with high turns ratios can be mounted directly onto PC boards with flying leads or pinned carriers.
These transformers are ideal for data center power monitoring, PDUs, branch circuit monitoring, industrial switchgear, load management systems, and tight panel applications where accurate current measurement and minimal EMI are essential. Every unit is built to your exact specifications in our Shelton, Connecticut facility, with scalable U.S. capacity and full engineering support.
Why Choose Bridgeport Toroidal Current-Sensing Transformers
Toroidal current-sensing transformers offer significant advantages over traditional designs thanks to their closed magnetic path and zero air gaps. This construction provides a uniform magnetic field that delivers superior accuracy, excellent linearity, and extremely low VA burden starting at just 1.0 VA – making them especially effective for monitoring and protection in modern electrical systems.
For data centers, industrial facilities, and OEMs working with space-constrained or performance-sensitive applications, the benefits include:
- Ultra-compact size with the smallest footprint in the industry, as small as 2.50″ OD × 1.00″ HT for maximum space savings in tight panels, PDUs, and equipment
- Superior accuracy and linearity from the uniform magnetic field and closed-loop toroidal construction
- Extremely low VA burden for better metering performance and longer secondary cable runs in monitoring systems
- Minimal electromagnetic interference (EMI) and stray fields due to the closed magnetic path
- Flexible finishing options including tape, resin dip, epoxy potting, or full epoxy casting for single or multi-phase assemblies
- Broad standard line plus fully custom designs built exactly to your specifications
- Made in the USA with consistent quality, Buy-American eligibility, and direct engineering support
Every Bridgeport toroidal current-sensing transformer is engineered and manufactured to your exact requirements in our Shelton, Connecticut facility, with full testing and scalable U.S. production capacity.
Current-Sensing Transformer Specifications
| P/N | Current Ratio | VA Burden (Examples) | Percent Accuracy | Finished Dimensions (OD x HT) |
|---|---|---|---|---|
| 0050-CTR | 50:5 | 1.0 | 2 | 2.50 x 1.00 in |
| 0075-CTR | 75:5 | 1.0 | 2 | 2.50 x 1.00 in |
| 0100-CTR | 100:5 | 2.0 | 2 | 2.50 x 1.00 in |
| 0200-CTR | 200:5 | 5.0 | 1 | 3.65 x 1.15 in |
| 0300-CTR | 300:5 | 12.5 | 1 | 3.65 x 1.15 in |
| 0400-CTR | 400:5 | 12.5 | 1 | 3.65 x 1.15 in |
| 0500-CTR | 500:5 | 25.0 | 1 | 4.10 x 1.25 in |
Toroidal current-sensing transformers shine in compact, high-accuracy, low-burden current measurement applications.
Data Centers & AI Infrastructure
Compact toroidal current transformers for data center PDUs, branch circuit monitoring, UPS systems, and load management
Industrial Manufacturing Facilities
High-performance low-burden toroidal CTs for industrial load monitoring, switchgear protection, and energy management systems
Commercial Buildings & Campuses
Space-saving toroidal current sensors for commercial switchgear, energy management, and power distribution monitoring
Switchgear & Electrical Distribution OEMs
Ultra-compact current transformers for OEM switchgear, distribution panels, protection relays, and monitoring applications
OEM Equipment & Control Panels
Small-footprint toroidal CTs for tight control panels, multi-phase assemblies, and custom OEM equipment integration
Let's build yours to spec.
Custom magnetics engineered and manufactured in the USA. Tell us your requirements and our engineers will help.
Frequently Asked Questions
What is a toroidal current-sensing transformer?
A toroidal current-sensing transformer (also called an instrument transformer) is a compact device that accurately measures current flowing through power lines and bus bars. The closed toroidal core design provides excellent linearity, low magnetizing current, and minimal electromagnetic interference, making it ideal for monitoring, protection, and energy management systems.
What are the advantages of toroidal current-sensing transformers?
Toroidal CTs offer several key advantages over traditional laminated designs, including a smaller footprint, superior accuracy and linearity, extremely low VA burden (starting at 1.0 VA), reduced EMI, and better performance in tight spaces. These benefits make them especially effective for data center monitoring, industrial load management, and OEM equipment.
What sizes of toroidal current transformers does Bridgeport manufacture?
Bridgeport produces ultra-compact toroidal current-sensing transformers as small as 2.50″ OD × 1.00″ HT. We offer a broad range of standard sizes plus fully custom dimensions to fit tight panels, PDUs, switchgear, and other space-constrained applications.
Why is low VA burden important in current transformers?
Low VA burden (starting at just 1.0 VA) allows the CT to deliver more accurate signals over longer secondary cable runs and reduces the load on connected meters, relays, and monitoring equipment. This is especially valuable in data centers, commercial buildings, and industrial facilities with distributed monitoring systems.
Can toroidal current-sensing transformers be used in data centers?
Yes. Compact toroidal CTs are well-suited for data center applications including PDU monitoring, branch circuit measurement, UPS input/output monitoring, and overall load management. Their small size, low EMI, and reliable performance make them a strong choice for space-limited environments.
What finishing and encapsulation options are available?
Bridgeport toroidal current-sensing transformers can be supplied with tape insulation, resin dipping, epoxy potting, or full epoxy casting. They are also available as fully encapsulated multi-phase assemblies for maximum durability in demanding industrial and commercial environments.
What is the difference between current-sensing and voltage-generating toroidal transformers?
Current-sensing transformers are designed to accurately measure current with low burden. Voltage-generating types use a higher turns ratio (typically 1000–2000) plus a load resistor to produce a voltage signal for electronic monitoring equipment. Both can be supplied with PC board mounting options.
Are Bridgeport toroidal CTs suitable for multi-phase applications?
Yes. We offer both individual units and fully encapsulated multi-phase toroidal current-sensing transformer assemblies, making them ideal for three-phase monitoring in switchgear, PDUs, and industrial distribution equipment.
