ABB OTM_C21D Compact Automatic Transfer Switch

The ABB OTM_C21D Compact Automatic Transfer Switch is designed for seamless switching between two power sources, compatible with both single-phase and three-phase power supplies. Packed with features, the OTM_C21D offers functionalities such as voltage loss detection, phase loss detection, over- and under-voltage monitoring, adjustable conversion delay, generator start and stop capabilities, on-site and remote testing, and more.

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The controller for the OTM_C21D Compact ATS provides versatile operation options, including manual conversion, button-based conversion, and automatic conversion. The automatic conversion modes comprise self-injection with self-recovery, mutual backup with self-injection, and no self-recovery. Within the automatic mode, various operating methods can be selected, including Line 1 priority, no-line priority, and manual back-switching mode.

Additionally, the OTM_C21D can be equipped with communication capabilities by incorporating the optional external Modbus RTU module. This enhances its functionality by allowing communication in line with industry standards.

introduction of OTM-C21D Compact ATS ABB construction

Features of OTM_C21D Compact ATS ABB

  • Reasonable structure, small volume, nice appearance, provided with protective shield, safer and more reliable power supply.
  • Complete protective functions, including short circuit, overload, open phase, and loss-of-voltage protection.
  • Noiseless, energy saving, simple installation, easy operation, reliable and stable performance.

Specification of OTM_C21D ATS

OTM_C21D ATS Parameters
Rated operational voltage Ue[V] Single-phase (2P)

Three-phase (3P/4P)


220~240 V AC 50~60 Hz


Frequency 50Hz/60 Hz
Operating voltage range 0.7~1.3 Ue
Measuring accuracy ±3%
Operating angle 90° ( O-I, I-O, O-II, II-O)

180° ( I-O-II, II-O-I)

OFF time 0,6 – 0,7 s
Total transfer time 2.5 s
Output relay utilization category 3A, AC1, 250V
Electromagnetic compatibility Class B
Ingress Protection Rating IP20, front panel
Rated impulse withstand voltage Uimp 8 kV (6 kV for the control circuit, disconnect the power line of the control circuit before carrying out the dielectric voltage withstand test)
Operating temperature -25~55oC
Transportation and storage temperature -40~70oC
Altitude Max. 2000 m

Applications of OTM_C21D ATS

ABB Compact ATS OTM_C21D is particularly suitable for applications that require high reliability of continuous power supply and where sudden power outages may cause serious problems, such as operating rooms, airports, hotels, banks, communication systems, and production lines, etc.

Dimensions of OTM_C21D Compact ATS

Dimensions of ABB Compact ATS OTM_C21D