🔍 Key Concepts

• Differences between magnetic trip and thermal trip elements in circuit breaker symbols • How a combined thermal-magnetic trip unit is usually shown in schematic form • Function of the circle/coil symbol vs. the zig‑zag/bimetal symbol in protection diagrams

💭 Think About

• Look closely at figure 3 and identify how many different types of trip elements are drawn in each pole path. What does the circle represent, and what does the zig‑zag element represent? • Compare figure 3 with figures 1 and 2 below it. Which one shows only instantaneous (short‑circuit) protection, and which shows only overload (time‑delay) protection? Then decide what protection figure 3 must provide. • Think about what kind of trip element arrangement you would expect on a general‑purpose molded‑case breaker used for both overload and short‑circuit protection.

✅ Before You Answer

• Verify which symbol in the drawing corresponds to a magnetic (instantaneous) trip element (usually a coil/solenoid symbol). • Verify which symbol corresponds to a thermal (overload/time‑delay) trip element (usually a bimetal/zig‑zag resistor‑like symbol). • Before choosing, confirm whether figure 3 shows one type of element only or both types in series in each phase. That will narrow the choices significantly.