Split-core current transformers for measuring AC current

AT, TT - Smart Grid and Automation Current transformers

The AT and TT family comprises split-core sensors designed for the electronic measurement of AC waveform currents while ensuring galvanic isolation between the primary circuit and the secondary circuit.

AT current transformers are known for their versatility in output types. They are available with either a current or voltage output, with options including 4-20 mA, 0-5 V, or 0-10 V. In addition, they feature a Terminal output and a 16 mm diameter aperture. These AT sensors also provide a RMS (average) output.

On the other hand, TT current sensors are offered with either an 8 mm or 16 mm diameter aperture and come with a 1-meter cable output for added flexibility in installation.

Both product series, AT and TT, are primarily tailored for use in the energy, smart grid, and automation domains, where accurate current measurements are crucial.

AT and TT split-core transducers rely on the current transformer technology, which is based on air-core technology.

AT, TT – Features and benefits

AT TT smart grid automation current sensors

Main characteristics

  • Split-core type
  • ⌀ 16 mm sensing aperture for non-contact measurement (TT components are also available with a ⌀ 8 mm aperture)
  • Insulating plastic case recognized according to UL 94-V0 
  • Terminal output for the AT Series
  • Cable output (1m) for the TT Series


  • High total error and low phase shift (TT)
  • High insulation between primary and secondary circuits
  • Compact case
  • Cost-effective solution
  • Easy installation

Typical applications

AT and TT products are purposefully manufactured for applications within the energy and automation domains. These split-core current sensors find utility in a wide variety of applications, including:

  • Automation and Supervision: Current measurement for process regulation by distributed PLCs or remote control (e.g. SCADA software)
  • Safety and Condition Monitoring: Load monitoring for protection systems and predictive maintenance (e.g. conveyers, pumps or HVAC motors) 

In addition, TT transducers can extend their use to the following applications:

  • Power meter: Current measurement for active power calculation
  • Energy sub-meters: For energy efficiency monitoring, consumption analysis and costs allocation
  • Power quality monitoring
  • Distributed measurement systems

LEM AT, TT – Download & Technical Characteristic

AT Series

Product Document Primary nominal RMS voltage Output Type Secondary Nominal Signal Value Op. Temperature
AT 5 B420L


5 A Current 4-20mA -20 to 60°C
AT 5 B5


5 A Voltage 0-5V -20 to 60°C
AT 5 B10 Datasheet 5 A Voltage 0-10V -20 to 60°C
AT 10 B420L Datasheet 10 A Current 4-20mA -20 to 60°C
AT 10 B5 Datasheet 10 A Voltage 0-5V -20 to 60°C
AT 10 B10 Datasheet 10 A Voltage 0-10V -20 to 60°C
AT 20 B420L Datasheet 20 A Current 4-20mA -20 to 60°C
AT 20 B5 Datasheet 20 A Voltage 0-5V -20 to 60°C
AT 20 B10 Datasheet 20 A Voltage 0-10V -20 to 60°C
AT 50 B420L Datasheet 50 A Current 4-20mA -20 to 60°C
AT 50 B5 Datasheet 50 A Voltage 0-5V -20 to 60°C
AT 50 B10 Datasheet 50 A Voltage 0-10V -20 to 60°C
AT 100 B420L Datasheet 100 A Current 4-20mA -20 to 60°C
AT 100 B5 Datasheet 100 A Voltage 0-5V -20 to 60°C
AT 100 B10 Datasheet 100 A Voltage 0-10V -20 to 60°C
AT 150 B420L Datasheet 150 A Current 4-20mA -20 to 60°C
AT 150 B10 Datasheet 150 A Voltage 0-10V -20 to 60°C


TT Series


Product Document Primary nominal RMS voltage Secondary Nominal Signal Supply Voltage range Op. Temperature
TT 50-SD


50 A Current 16.66 mA -25 to 70°C
TT 100-SD


100 A Current 33.33 mA -25 to 70°C


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