Split-core current transformer with high accuracy and low phase shift.

ATO - Split-core current transformers

The ATO current sensors are split-core current transformers characterized by high accuracy and low phase shift. 

They are precisely designed for the electronic measurement of AC waveform current, ensuring galvanic separation between the primary circuit (power) and the secondary circuit (measurement). Covering a range from 0 A to 125 A, these current transformers are primarily intended for mounting on the primary circuit.

ATO split-core current transformers are versatile, offering both current and voltage outputs. With compact dimensions, self-powered functionality, and apertures ranging from 10 mm to 16 mm in diameter, they are well-suited for various applications. Additionally, these transformers feature a 1-meter-long cable output.

Utilizing air-core technology, the ATO current transformers are particularly suitable for new Smart-Grid applications, meeting stringent standards such as IEC 61869 for ratio error and phase displacement.

ATO – Features and benefits

ATO Series


  • Split-core current transformer
  • Application up to 600 V CAT III PD2, basic insulation
  • Accuracy class 1 (IEC 61869-2) and class 3 (IEC 61869-2)
  • Current or Voltage output
  • ⌀ 10 mm to 16 mm sensing aperture
  • 1 m output cable
  • Very low-cost solution
  • Compact
  • Self-powered
  • Slot for attaching the current transformer on the primary with plastic tie
  • DIN rail adapter (optional)


  • No interruption of electricity during installation on insulated conductors
  • Quick, non-intrusive and easy setup
  • Provide a calibrate output

Typical applications

The ATO sensor family is well-suited for various applications in the smart grid, such as:

  • Hybrid inverter (Home Energy Storage)
  • Power metering: current measurement for active power calculation
  • Building sub-metering: energy efficiency monitoring, consumption analysis and cost allocation
  • Power quality monitoring: electrical loads and distribution system equipment
  • Distributed measurement systems
  • Condition monitoring (e.g. Motor loads such as conveyers, pumps)

LEM ATO – Download & Technical Characteristic

Product Document Primary nominal
RMS voltage
Secondary Nominal
Supply Voltage range Op. Temperature
ATO-5-B420-D10/SP4 - 4m cable output


5 A Current 20 to 28 -10 to 55 °C
ATO-10-B225-D10/SP3 ATO XDK


10 A Voltage Self-Powered -10 to 55 °C
ATO-75-B1I-D10 Datasheet 75 A Voltage Self-Powered -10 to 55 °C
ATO-75-B333-D10 Datasheet 75 A Current Self-Powered -20 to 70 °C
ATO-100-B333-D16 Datasheet 100 A Voltage Self-Powered -10 to 55 °C
ATO-125-B1I-D16 Datasheet
125 A Current Self-Powered -20 to 70 °C
ATO-125-B225-D16 Datasheet 125 A Voltage Self-Powered -10 to 55 °C


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