Korean Electrician Glossary — MCCB, MC, EOCR, TB Explained
Last updated: 2026-06-28 · 4 min read
The Korean Electrician (전기기능사) practical schematics are full of part abbreviations like MCCB, MC, EOCR and wiring terms like self-hold, interlock, pass-through wiring. This page collects the ones people mix up most, defines each in a line, and links straight to the guide that covers it in full. Look a term up here first when one trips you up.
The main parts you meet on the Korean Electrician practical, at a glance.
Power & protection
Term
Meaning
MCCB (molded-case circuit breaker)
Switches the main circuit on/off at the panel entry and trips on overcurrent or a short. → MCCB & fuse
Fuse
Overcurrent protection for the control circuit. Wire colour switches from the main circuit to the control circuit (yellow) at this point. → MCCB & fuse
EOCR (electronic overload relay)
Watches the motor current and breaks the circuit through its trip contacts when an overload occurs. → EOCR overload relay
PE (protective earth)
The green earth conductor. Normally carries no current, but on a leak it routes current to ground to prevent shock. → Sequence control & contacts
Switching & control parts
Term
Meaning
MC (magnetic contactor)
A large relay whose mains contacts close when the coil energises, feeding 3-phase to the motor. Its aux contacts handle self-hold and interlock. → Magnetic contactor (MC)
Relay (8-pin relay)
A control switch where the coil (2·7) drives two contact sets (1-3-4 / 8-6-5) at once. → 8-pin relay
Timer (T, time-delay relay)
A relay whose contacts change only after a set delay. On-delay (TON) action. → Timer relay
FR (flicker relay)
Cycles its contacts on/off at a fixed interval to make a lamp blink. → Problem 1 analysis
FLS (floatless switch)
A liquid-level relay that starts and stops a pump based on water level. → Problem 1 analysis
LS (limit switch)
A detection switch that trips when an object reaches an end stop; used for end detection in forward/reverse, with an SPDT structure. → Problem 14 control circuit
SS (selector switch)
A turn-knob switch for choosing the run mode — manual, auto, and so on. → Problem 1 analysis
PB (push button)
A self-returning contact that acts only while pressed. Red = stop, green = start. → Sequence control & contacts
Wiring a relay/MC a-contact in parallel with the start button so the action holds after you release it. → The self-hold circuit
Interlock
Using each MC's b-contact to stop the two from ever closing together. Omit it in forward/reverse and you fail on a 3-phase short. → Problem 14 control circuit
