The magnetic blowout coil produces a magnetic field between the breaking contacts that forces the arc up, increasing the length of the arc and causing it to dissipate faster. Which coil is this?

• A. Hold-in coil
• B. Blowout coil
• C. Shunt coil
• D. Booster coil

Answer: (B)

When a breaker opens, an arc forms between the breaking contacts. To quench it quickly, you want to lengthen and dissipate the arc. The blowout coil sits around the arc path and, with current flowing, creates a magnetic field between the contacts. This field pushes the arc upward and away from the contacts, making the arc longer. A longer arc has higher impedance and is cooled and de ionized more effectively, causing the arc to dissipate faster.

That specific action—driving the arc upward to elongate and extinguish it—is the function of the blowout coil. Hold-in coils are used to hold the contact closed, booster coils assist opening in a different way, and shunt coils serve other flux-control purposes, not the arc-blowout effect described.