Shading coils are used with AC relays to prevent:

• A. They protect against overload
• B. They increase coil heating
• C. They reduce arc distance
• D. They are used to prevent contact chatter and hum

Answer: (D)

Shaded coils provide a small, delayed magnetic pull to keep the relay’s armature attracted as the AC current swings through zero. The copper shading ring around part of the pole piece gets an induced current that lags behind the main magnetic field. This lagging flux keeps the contacts engaged a fraction of a cycle, smoothing the make-and-break action. The result is less contact chatter and reduce audible hum. This feature is not about protecting against overload, increasing coil heating, or altering arc distance—the primary purpose is to stabilize the contact operation on AC.