Current Transformers

Current transformers (CT) are devices that are used to transform the current from a high current into a lower current so that the power can then be measured and controlled. The transformers consist of a core, a primary and a secondary winding. When an alternating current flows through the primary winding, a magnetic flux is created which then induces an alternating current in the secondary winding. This alternating current is proportional to the current in its primary. Current transformers are also known as a "step-down transformers". Once the current has been reduced it can be safely monitored and measured using an ammeter.


Current transformers can perform circuit control and perform roles for safety protection and current limiting.


Current transformers are found in:


  • Generating stations,

  • Electrical substations

  • Commercial electric power distribution.

Types of Current Transformers


Toroidal Current Transformer - These transformers are shaped like a doughnut they do not contain a primary winding. Instead, the line that carries the current flowing in the network is threaded through a window or hole in the toroidal transformer. Toroidal transformers offer high efficiency with minimal excess noise and little excess leakage inductance.


Wound Current Transformer - The transformers primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit. The magnitude of the secondary current is dependent on the turns ratio of the transformer.


Bar-type Current Transformer – This type of current transformer uses the actual cable or bus-bar of the main circuit as the primary winding, which is equivalent to a single turn. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device.


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Description Price Current Ratio Inner Diameter Transformer Type Overall Height Overall Width Overall Depth Input Current Output Current Minimum Temperature Maximum Temperature Dimensions For Use With Mounting Type Series
RS Stock No. 175-6220
Mfr. Part No.4NC5441-2DN21
BrandSiemens
TWD4,805.00
Each
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3000:5 - Window 84.1mm 112mm 127.5mm 3kA 5 A -30°C +55°C 112 x 127.5 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6214
Mfr. Part No.4NC5438-2CJ21
BrandSiemens
TWD3,434.00
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2000:5 - Window 84.1mm 112mm 127.5mm 2kA 5 A -30°C +55°C 112 x 127.5 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6160
Mfr. Part No.4NC5222-2CE21
BrandSiemens
TWD1,872.00
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200:5 - Window 67.6mm 60.6mm 78.4mm 200A 5 A -30°C +55°C 60.6 x 78.4 x 67.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6222
Mfr. Part No.4NC5923-5LT21
BrandSiemens
TWD112.00
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- - - - - - - - - - - 4NC51 Current Transformers H-Rail Mount Sentron
RS Stock No. 175-6130
Mfr. Part No.4NC5112-2CB21
BrandSiemens
TWD1,872.00
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50:5 - Window 65.6mm 60mm 75.3mm 50A 5 A -30°C +55°C 60 x 75.3 x 65.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6161
Mfr. Part No.4NC5222-2DE21
BrandSiemens
TWD2,166.00
Each
units
200:5 - Window 67.6mm 60.6mm 78.4mm 200A 5 A -30°C +55°C 60.6 x 78.4 x 67.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6156
Mfr. Part No.4NC5125-2FE21
BrandSiemens
TWD2,220.00
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300:5 - Window 65.6mm 60mm 75.3mm 300A 5 A -30°C +55°C 60 x 75.3 x 65.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6189
Mfr. Part No.4NC5327-2DE21
BrandSiemens
TWD2,195.00
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600:5 - Window 84.1mm 82.5mm 98mm 600A 5 A -30°C +55°C 82.5 x 98 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6122
Mfr. Part No.3UL2302-1A
BrandSiemens
TWD6,374.00
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- - Toroidal Ring 64mm 70mm 75.5mm 30 mA → 40 A 85 A -25°C +60°C 70 x 75.5 x 64 mm Fault Current Monitoring Chassis Mount, DIN Rail -
RS Stock No. 175-6215
Mfr. Part No.4NC5438-2DL21
BrandSiemens
TWD4,613.00
Each
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2000:5 - Window 84.1mm 112mm 127.5mm 2kA 5 A -30°C +55°C 112 x 127.5 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6184
Mfr. Part No.4NC5326-2CE21
BrandSiemens
TWD2,192.00
Each
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500:5 - Window 84.1mm 82.5mm 98mm 500A 5 A -30°C +55°C 82.5 x 98 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6223
Mfr. Part No.4NC5925-5LT21
BrandSiemens
TWD131.00
Each
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- - - - - - - - - - - 4NC52 Current Transformers H-Rail Mount Sentron
RS Stock No. 175-6170
Mfr. Part No.4NC5225-0CE21
BrandSiemens
TWD2,066.00
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400:1 - Window 67.6mm 60.6mm 78.4mm 400A 1 A -30°C +55°C 60.6 x 78.4 x 67.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6131
Mfr. Part No.4NC5113-0CB21
BrandSiemens
TWD2,217.00
Each
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60:1 - Window 65.6mm 60mm 75.3mm 60A 1 A -30°C +55°C 60 x 75.3 x 65.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6225
Mfr. Part No.4NC5940-5LT21
BrandSiemens
TWD160.00
Each
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- - - - - - - - - - - 4NC54 Current Transformers H-Rail Mount Sentron
RS Stock No. 175-6123
Mfr. Part No.3UL2303-1A
BrandSiemens
TWD6,808.00
Each
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- - Toroidal Ring 64mm 92mm 98mm 30 mA → 40 A 150 A -25°C +60°C 92 x 98 x 64 mm Fault Current Monitoring Chassis Mount, DIN Rail -
RS Stock No. 175-6173
Mfr. Part No.4NC5225-2DE21
BrandSiemens
TWD2,323.00
Each
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400:5 - Window 67.6mm 60.6mm 78.4mm 400A 5 A -30°C +55°C 60.6 x 78.4 x 67.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6211
Mfr. Part No.4NC5435-2DH21
BrandSiemens
TWD3,492.00
Each
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1500:5 - Window 84.1mm 112mm 127.5mm 1.5kA 5 A -30°C +55°C 112 x 127.5 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6150
Mfr. Part No.4NC5123-0CE21
BrandSiemens
TWD2,066.00
Each
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250:1 - Window 65.6mm 60mm 75.3mm 250A 1 A -30°C +55°C 60 x 75.3 x 65.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 175-6152
Mfr. Part No.4NC5123-2CE21
BrandSiemens
TWD1,872.00
Each
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250:5 - Window 65.6mm 60mm 75.3mm 250A 5 A -30°C +55°C 60 x 75.3 x 65.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron