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Custom Toroidal Transformers
At Bridgeport Magnetics Group, we help OEMs and engineers get exactly the toroidal transformer they need - fast, reliable, and built to their exact specifications. Our Custom Toroidal Transformers are designed and manufactured entirely in-house at our 45,000 sq ft vertically integrated facility in Shelton, Connecticut. From core winding and heat treatment all the way through testing of the final transformer, every step is controlled under one roof - delivering unmatched quality, shorter lead times, and complete customization that empowers you to meet the most demanding power requirements of your application.
Custom Toroidal Transformers Made in the USA
Since 1982, Bridgeport Magnetics has designed and manufactured high-performance toroidal transformers across a power range of 30 VA to 65,000 VA (65 kVA). Our toroidal designs are 40–50% lighter than traditional E-I laminated transformers of equivalent rating, with measurably lower electromagnetic interference, higher efficiency, and quieter operation. Whether you need a single prototype or production quantities of several thousand units, Bridgeport Magnetics offers full in-house design, winding, and testing under one roof.
We maintain total vertical control over our materials and manufacturing processes, delivering the quality, repeatability, and performance that few manufacturers can match.
Custom Toroidal Transformer Solutions
Enclosed single- and three-phase systems built on the Power Tower platform, which stacks multiple toroidal core-and-coil assemblies to deliver high power in a compact footprint.
Single-phase toroidal power and isolation transformers up to 70 kVA (350 kVA three-phase), in step-up, step-down, and isolation configurations with custom voltages and taps.
Compact toroidal O-core transformers providing galvanic isolation, with electrostatic (Faraday) shielding between windings to reduce coupled electrical noise.
Standard Current Transformers
Toroidal current transformers for accurate metering, protection, and monitoring across common ratios and accuracy classes.
Our Toroidal Transformer Product Lines
Standard Toroidal Power Transformers
Our toroidal power transformers cover the core of what most engineers need: single-phase step-up, step-down, and isolation configurations from 30VA to 65kVA.
Standard models ship with common voltage combinations (120V, 240V, 277V primaries with a range of secondary voltages), while custom designs accommodate any input/output voltage combination within our power range.
Standard features include Class B (130C) or Class F (155C) insulation, vacuum-impregnated windings for moisture resistance and vibration damping, and UL/CSA recognition. Lead configurations range from flying leads to terminal block mounting.
Toroidal Isolation Transformers
Custom isolation transformers provide galvanic separation between the primary and secondary circuits. Our isolation transformer designs include electrostatic (Faraday) shields between windings to reduce capacitive coupling and common-mode noise.
Key specifications include dielectric withstand ratings from 2,500V to 4,000V (higher on request), leakage current performance below 300 microamps (below 100 microamps for medical-grade units), and optional electrostatic shields. Isolation transformers are available in both single-phase and three-phase configurations.
Applications range from shore power protection on marine vessels to patient-contact medical equipment to industrial motor drive isolation.
3-Phase Toroidal Transformers
Three-phase toroidal transformers serve industrial and commercial applications requiring balanced three-phase power. Bridgeport Magnetics manufactures 3-phase toroidal configurations from 3kVA to 375kVA using three individual toroidal cores connected in delta, wye, or delta-wye arrangements.
The toroidal geometry offers a particular advantage in three-phase applications: three individual toroids mounted in a common enclosure weigh significantly less than a single three-phase E-I transformer of the same rating, while offering better thermal management because heat is distributed across three separate core-and-coil assemblies rather than concentrated in one stack.
High-Power Toroidal Transformers (up to 65kVA)
For applications demanding higher power, our Power Tower transformer platform delivers toroidal performance up to 65,000 VA (65 kVA). The Power Tower design stacks multiple toroidal core-and-coil assemblies in a vertical configuration, providing high-power output in a compact vertical footprint.
High-power toroidal transformers from Bridgeport Magnetics are engineered for demanding applications including large marine vessel shore power systems and marina dock-side distribution, industrial motor drives and automation, data centers and critical power infrastructure, energy storage and renewable energy systems, and commercial EV charging stations.
All units are custom-engineered to the application, with thermal management, mounting provisions, and enclosure options tailored to the installation environment. Whether you need a single unit or multiple transformers for a complete system, Bridgeport Magnetics offers full in-house design, winding, and testing under one roof in our Shelton, CT facility.
Toroidal Current Transformers
Toroidal current transformers (CTs) provide accurate current measurement for metering, protection, and monitoring systems. Our standard current transformers cover common ratios and accuracy classes, while custom CT designs support specialized ratios, extended frequency ranges, and application-specific accuracy requirements.
Toroidal geometry is particularly well-suited to current transformer applications because the closed magnetic path provides excellent linearity and low phase error across a wide current range. Bridgeport Magnetics manufactures CTs for utility revenue metering, industrial power monitoring, protective relay systems, and precision laboratory measurement.
Custom Toroidal Transformer Design
The majority of toroidal transformers we ship are custom designs. Bridgeport Magnetics has been engineering custom magnetic solutions since 1982. Our design process is built for efficiency, from your initial specification through prototype delivery and production ramp.
Design Capabilities
Our engineering team works with you from concept through production. Because we manufacture our own toroidal transformer cores and wind our own coils using flat magnet wire and round magnet wire, lead times are shorter and more predictable than shops that source cores and materials from third parties.
- Specification review. You provide electrical requirements (voltages, VA rating, frequency, isolation needs), physical constraints, and certification requirements. If you have a complete spec document, we can often return a preliminary design within 24-48 hours. If you have a rough concept, our engineers help refine the specification.
- Design and simulation. We model the transformer’s electrical, magnetic, and thermal performance to ensure the design meets your requirements across the full operating range, including worst-case conditions for temperature rise, regulation, and inrush current.
- Prototype build and test. First articles are built and tested in our Shelton, CT facility. Test data is provided for your review.
- Production. Approved designs move into production with full traceability. Our winding machines, core-cutting equipment, and testing stations handle runs from single units to thousands per month.
Specifications We Support
If your application falls outside these ranges or requires non-standard parameters, contact our engineering team to discuss feasibility.
| Parameter | Range |
|---|---|
| Power Rating | 30VA to 65kVA (375kVA for 3-phase) |
| Input Voltage | Any standard or non-standard voltage |
| Output Voltage | Single or multiple secondaries, any voltage |
| Frequency | 50Hz, 60Hz, 400Hz, and custom frequencies |
| Phases | Single-phase and three-phase |
| Insulation Class | Class A (105C) through Class H (180C) |
| Dielectric Withstand | 2,500V to 4,000V standard; higher on request |
| Leakage Current | Down to <100 microamps (medical-grade) |
| Mounting | Center bolt, bracket, chassis, PCB, encapsulated |
| Terminations | Flying leads, terminal blocks, connectors, custom |
Certifications: UL, ETL (Intertek), CSA, EN, IEC
Bridgeport Magnetics Group designs and manufactures transformers to meet the following safety standards:
UL
UL 506 (Specialty Transformers), UL 1585 (Class 2 and Class 3 Transformers), UL 5085 (Low-Voltage Transformers). UL recognition is required for most commercial and industrial products sold in the United States.
ETL
(Intertek)
ETL Listed to UL 506 , UL 1585 , and UL 5085. ETL certification is widely accepted for commercial and industrial products sold in the United States and Canada..
IEC
(International Electrotechnical Commission)
IEC 61558, IEC 60601-1 (medical electrical equipment), IEC 61010 (measurement/laboratory equipment).
CSA
(Canadian Standards Association)
Required for products entering the Canadian market. Bridgeport transformers carry dual UL/CSA recognition.
EN
(European Norm)
EN 61558 series for safety of power transformers, power supplies, reactors, and similar products.
If your product requires specific agency certification marks, specify this when you contact us for your custom design. Designing for certification from the start avoids costly redesigns and delays later in your product development cycle. Our engineering team understands the creepage, clearance, dielectric, and leakage requirements for each standard and designs accordingly.
Applications & Industries
Toroidal transformers from Bridgeport Magnetics serve a broad range of industries. The combination of compact size, low EMI, high efficiency, and quiet operation makes toroidal geometry the right choice for applications where performance matters as much as the cost.
Data Centers & Critical Power
The Benefits of Custom Toroidal Transformers
Toroidal transformers use a donut-shaped core wound from a continuous strip of grain-oriented silicon steel (GOSS). The windings are distributed evenly around the entire circumference of the core, creating a nearly closed magnetic circuit. This design produces four measurable advantages over conventional E-I laminated transformer designs.
40-50% Lighter and Smaller Than E-I Designs
A toroidal transformer is physically smaller and significantly lighter than an E-I transformer with the same VA rating. The weight reduction typically falls between 40% and 50%. This affects shipping costs, mounting requirements, and structural loading. In mobile and transportation applications, every pound counts.
Use Case Scenarios: A 5kVA E-I transformer might weigh 55-60 pounds and occupy a footprint of roughly 10" x 10" x 8". A toroidal transformer at the same 5kVA rating weighs approximately 28-32 pounds and can fit within a 9" diameter by 4" height envelope. When space is limited, every inch counts: marine engine rooms, medical equipment housings, rack-mounted industrial systems, and wall-mounted utility panels.
Lower Electromagnetic Interference (EMI)
In a toroidal design, the toroidal winding covers the full circumference of the core, so the magnetic field is largely self-contained. Stray magnetic flux (the primary source of radiated EMI from power transformers) is reduced by up to 90% compared to E-I designs. In many cases, a toroidal transformer eliminates the need for additional magnetic shielding, reducing total system cost and complexity.
Use Case Scenarios: This makes toroidal transformers the preferred choice for systems with sensitive electronics nearby: medical diagnostic instruments, audio recording equipment, precision measurement devices, and communication systems.
Higher Efficiency and Reduced Core Losses
A toroidal core is made up of continuous grain-oriented steel, providing a low-reluctance magnetic path. Core losses (aka iron losses) in toroidal designs run approximately 50-70% lower than in equivalent E-I transformers.
Total operating efficiency for toroidal transformers falls between 97%-99%, depending on the specific design and operating conditions. No-load losses, the power consumed when the transformer is energized but not delivering load current, are particularly low.
Use Case Scenarios: Reduced core losses and higher efficiency matter for transformers that remain powered around the clock, such as standby power supplies, medical equipment, and building distribution systems, where cumulative energy waste adds up over years of operation.
Quieter Operation (Lower Audible Hum)
E-I laminated transformers are known for the characteristic 60Hz (or 50Hz) hum caused by magnetostriction. This is the slight physical vibration of loosely stacked laminations in an alternating magnetic field. This hum can reach 40-50 dB in standard E-I designs.
Toroidal transformers, wound from a single continuous strip of steel with no air gaps in the magnetic path, produce significantly less audible noise, typically below 30 dB, and often below the ambient noise floor.
Use Case Scenarios: For audio systems, recording studios, medical environments, residential installations, and any application where acoustic performance matters, quiet operation is not a luxury. It is a specification requirement.
Request a Quote for Your Custom Toroidal Transformer
Bridgeport Magnetics engineers custom toroidal transformers from 30VA to 65,000VA, precision-engineered in Shelton, CT with full in-house design, winding, and testing. Whether you need a single prototype or ongoing production quantities, our engineering team is ready to review your specification and provide a detailed quote.
For custom toroidal transformers, please include:
- Primary and secondary voltages
- VA rating
- Operating frequency
- Certification requirements (UL, CSA, IEC, EN)
- Physical size constraints (if applicable)
- Application Details
- Quantity and timeline
Preliminary quotes are typically returned within 24-48 hours. All design and manufacturing takes place in our Shelton, Connecticut facility. There is no outsourcing, no import delays, and no surprises.
Custom toroidal power. Built in the USA.
Toroidal transformers engineered, wound, and tested in Shelton, Connecticut since 1982 — trusted by OEMs and engineers across North America.
Frequently Asked Questions
What is a toroidal transformer?
A toroidal transformer is a power transformer built on a donut-shaped (toroidal) core, typically wound from a continuous strip of grain-oriented silicon steel. The primary and secondary windings are wound uniformly around the full circumference of the core. This geometry creates a nearly ideal magnetic circuit with minimal flux leakage, resulting in a transformer that is smaller, lighter, more efficient, and quieter than traditional E-I laminated transformer designs of the same power rating.
What are the advantages of toroidal transformers?
Toroidal transformers offer four primary advantages over E-I laminated designs. They are 40-50% lighter and smaller at the same VA rating, making them easier to mount and fit into tight enclosures. They also produce up to 90% less stray electromagnetic field, reducing interference with nearby sensitive electronics. Toroidal transformers operate at higher efficiency (95-99%) with significantly lower core losses, saving energy over the transformer’s operating life. Lastly, they produce far less audible noise — typically below 30 dB — because the single-strip wound core eliminates the magnetostriction-driven hum common in stacked lamination designs.
What sizes of toroidal transformers does Bridgeport Magnetics make?
Bridgeport Magnetics designs and manufactures toroidal transformers from 30VA to 65,000VA (65kVA). This range covers everything from small signal and instrumentation transformers to high-power industrial and marine shore power units. Both single-phase and three-phase configurations are available. Custom designs are engineered to your exact electrical and mechanical specifications.
How do I request a custom toroidal transformer quote?
To request a quote, provide your basic electrical specifications: primary voltage, secondary voltage(s), VA rating, operating frequency, and any certification requirements. Physical size constraints, mounting preferences, and environmental conditions (ambient temperature, indoor/outdoor use) are also helpful. You can submit this information through our request a quote page or call our engineering team directly at (203) 954-0050. Preliminary design quotes are typically returned within 24-48 hours.
What certifications do your toroidal transformers carry?
Bridgeport Magnetics designs and manufactures transformers to UL, ETL, CSA, EN, and IEC standards. This includes UL 506, UL 1585, UL 5085, EN 61558, IEC 61558, and IEC 60601-1 for medical applications. Specific certification marks are applied based on the requirements of your end product and target market. We recommend specifying certification requirements at the quoting stage so the design incorporates all necessary creepage, clearance, and testing requirements from the start.