Electronic devices can be influenced or can influence each other by electromagnetic fields. This interference should be reduced to a tolerable level. This is the topic of Electromagnetic compatibility. (EMC)
Along with a suitable EMC design magnetic components such as current compensated chokes can help to meet EMC requirements. They often are called common mode chokes (CMC) because differential mode currents can pass, and common mode currents are suppressed.
And important parameter is the insertion loss.
High permeability toroidal ferrites can be used for a low-cost standard component. To achieve high inductance values with compact dimensions nanocrystalline tape wound are often a better choice.
Single-phase current compensated chokes have 2 windings, while for three-phase systems 3 or 4 (with neutral) windings are required.
The windings must be insulated for operating voltages and provide necessary clearances and creepage distances.
Mechanical construction can either use through hole pinning or surface mount technology SMT.