MCCB and Fuse — the Panel's Two Protectors
From here you're in the main-circuit (주회로) parts block. We'll trace the path electricity takes from the panel inlet down to the motor, one part at a time. First up: the two protectors guarding the panel entrance — the MCCB (molded-case circuit breaker) and the fuse. The L1 brown · L2 black · L3 gray · PE green conductors from Sequence control basics meet the MCCB the instant they enter the panel.
MCCB — the main breaker that protects the whole panel
- When a fault drives current above its rating, it trips internally and cuts the whole panel in one shot.
- Its killer feature is that it resets — fix the cause, throw the handle back up, and it's back in service. That's why it always sits at the panel inlet.
- Top three pins (1·2·3) = input (L1·L2·L3); bottom three (4·5·6) = output. They pair by column (1-4 · 2-5 · 3-6) — one circuit per phase.
Fuse — the single-use protector you replace once it blows
A fuse does the same job as an MCCB but with a different mechanism. Meet a current above its rating and the metal element inside melts open — and once blown, that fuse is dead. The operator swaps in a new cartridge.
So why fit both a breaker *and* a fuse? They protect different things.
- MCCB → main circuit (heavy current) — guards the motor-side path against major faults.
- Fuse → control circuit (light current) — protects small loads like relay coils, buttons, and lamps in their own branch.
And a blown fuse leaves a clear physical trace that *something went wrong*, forcing the operator to investigate before reapplying power.
Main circuit vs control circuit — the color changes at the fuse
The conductors entering the fuse are brown (L1) and gray (L3), but the ones leaving it are yellow. That's not a mistake — it's the rule. The fuse straddles the boundary: above it is the main circuit (heavy current); below it is the control circuit (signal).
The full color and terminal rules are in Wire color & terminal rules.
Next
The part below the breaker that actually switches the motor on and off is next — the MC (magnetic contactor). It's the 8-pin relay's "coil flips the contacts" principle, just sized up for motor current.
Try it yourself
Toggle the breaker in the Korean Electrician practical simulator →