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Current Transformers (CTs)

Custom Designs

There are 2 main applications for Current Transformers (CTs); measuring power/current and for control or protective purposes.  

Toroid Corporation specializes in custom designed Current Transformers for both of these applications with an emphasis on the control and protective uses.

Traditionally, current transformers have been designed with a standard secondary current of 5 Amps which is used with conventional analog instruments and meters. Many control designs still utilize this standard concept which in many cases necessitates a mechanically larger unit than needed when hooked up to an op-amp or similar electronic circuits.

Toroid Corporation designs and manufactures current transformers of various types measuring currents from microamps up to thousands of amperes, and an internal diameter (window) that can range from 5 mm to 250 mm or larger. We design according to the specific needs of each customer with regard to the dimensions and electrical characteristics. Toroid Corporation offers different types encapsulation such as mylar, epoxy resin, lace & varnish or plastic enclosure with isolation up to 7.5 kV.

Please contact us and give us your requirements and we will work with you to get the minimum sized design and most cost-effective solution.

Electrical Parameters

The current transformer (or CT) detects or measures the electrical current flowing in a cable or power strip, converting it into a smaller current to be used in a measuring instrument or electronic circuit. The use of a CT is advantageous compared to designing instruments and electronic circuits to operate at high currents which is impractical and costly.

The CT used in electrical circuits measures the current under normal conditions, spikes and power outages, providing greater control over the system.  CT’s also have another big advantage which is the insulation between the meter and the circuit being measured. 


Standard Designs

Toroid Corporation offers two low cost standard design current transformers. Both are used in applications where you want to detect or measure AC-currents with no need for tight tolerances. Typical applications include power limiting controllers for air conditioning equipment, electrical heating systems, electrical furnaces, and motor drives.

The Current Transformers are designed using a core of tape wound, grain-oriented, silicon steel. 
• The -S versions are encased in a sturdy plastic housing and have mounting ears and 15” leads.
• The -PC versions are potted into plastic housings and are PC mountable.
• The TR 12525 versions are potted into sturdy plastic housings and come with 15” leads.


The listed designs are also available without encapsulation and multi-stranded leads. Please call our Customer Service Department for prices and availability. Other secondary turns and sizes are available upon request.


15” Leads PC Mount Turns Current range Max Sec Voltage
TR 3025-S TR-3025-PC 1:300 0-90 A 4.5 V
TR 5025-S TR-5025-PC 1:500 0-90 A 8.0 V
TR 10025-S TR-10025-PC 1:1000 0-90 A 16 V
TR 20025-S TR-20025-PC 1:2000 0-90 A 32 V
TR 30025-S TR-30025-PC 1:3000 0-90 A 48 V
TR 12525 N/A 1:1250 0-375 A 45 V

Please contact the company directly to purchase Part Numbers without a "Buy" icon next to it.

Need custom specifications for your transformer? Click here.


Part No. 1-9 Pieces 10-24 Pieces 25-99 Pieces
TR 3025-S $19.21 $16.40 $14.99
TR 10025-S $21.13 $18.05 $16.48
TR 12525 $28.85 $27.70 $25.82
 TR 3025-PC
 $19.21 $16.40 $14.99  
For larger quantity prices, please contact our factory sales department
Mechanical Dimensions:
P/N TR 3025-S P/N TR 12525

Terms and Conditions

  • For larger quantity prices, please contact the factory directly.
  • Prices and data subject to change without prior notice
  • Delivery: Small quantities of standards are normally available from stock
  • 30-Day Return Policy of Undamaged Items - 15% Restocking Fee on Standard Transformers
  • 36 Month Product Warranty
  • Terms and Conditions