Tuning reactors are connected with capacitors to tuned filter circuits with resonances in the audio frequency range for reducing, blocking or filtering harmonics or communications frequencies. The tuning reactors are connected either in a parallel configuration in the system, with system voltage applied across them, or in a series configuration with load current flowing through them.

With regard to installation, these devices may be identified as:

• Single phase or three phase
• Cast resin dry type, conventional dry type or oil immersed
• With or without magnetic shield
• For indoor or outdoor installation
• With or without enclosure
• With fixed or variable reactance