Korean Electrician Public Problem 1 — Full Wiring Walkthrough

Last updated: 2026-06-18 · 5 min read

Public Problem 1 of the Korean Electrician practical exam runs two motors, chosen by a selector switch (manual / auto); in auto, it is controlled by a water tank's level (a floatless relay), and a flicker relay flashes a lamp and buzzer as an alarm. Don't let the part count scare you — the backbone is a single self-holding circuit, and everything else just sits on top of it. Let's follow it through with three drawings.

At a glance — what builds what

1. Device layout — what goes where

• The control box (400×420) is central; operator devices live in control boxes *outside* the panel.
• Conduit is specified in three kinds — ① PE conduit, ② flexible conduit, ③ cable. The number *is* the conduit type, so follow the ①②③ on the drawing exactly.
• Where conduits split or join, you place an octagonal junction box (J) — the only legal branch point on a conduit run.
• TB1–TB4 are field terminal blocks outside the panel; they tie the motors, supply, and operator devices back to the panel.

2. Panel interior — the parts inside the box

The inside is simple. Two terminal-block rows top and bottom (TB5·TB6), with two rows of parts between them.

• Upper row: F · EOCR · MCCB · X · FR
• Lower row: T · FLS · MC1 · MC2

Every wire inside the box reaches the outside world (operator devices, motors) *through* these two terminal blocks. Parts don't run wires straight out of the box.

3. The main circuit — from supply to motor

Trace the main circuit as one trunk:

1. TB1 (L1·L2·L3·PE) brings in 3-phase 220 V.
2. MCCB switches all three phases at once.
3. EOCR watches the current — on overload it trips and cuts the control circuit.
4. The supply splits to MC1·MC2, and each contactor feeds its motor, M1·M2.

Wire colors follow the main-circuit rule — L1 brown · L2 black · L3 gray, with earth (PE) green. (The control circuit is yellow.) For the full color rule, see Wire color & terminal rules.

4. The control circuit — self-hold is the backbone

The control circuit on the right looks busy, but its center is a single self-hold latch. Press PB1 to start, and relay X holds itself in through its own a-contact; press PB0 to release it (see self-holding circuits). Every other part just adds a condition to that latch.

• SS (selector) — picks manual (M) / auto (A). Manual runs from buttons; auto runs from the water level.
• PB1 (green) · PB0 (red) — start / stop. Stop is always a b-contact (NC) in series.
• X (8-pin relay) — the aux relay that takes the start signal, self-holds, and drives the contactors.
• FLS + electrodes E1·E2·E3 — three electrodes in the tank sense the water level and switch the motor on/off in auto.
• T (timer) — used for time-delayed action.
• RL·GL — not run/stop lamps, but each lit by an MC aux a-contact: RL follows MC1, GL follows MC2. They tell you which motor is running, not a generic run-vs-stop state.
• FR (flicker relay) + YL·BZ — idle in normal operation. When the EOCR trips, that trip signal drives FR, which flashes YL (alarm lamp) and BZ (buzzer) alternately. So FR isn't an always-on alarm — it's an alarm branch that fires only on an overload fault.
• EOCR — on overload two things happen at once: its b-contact opens, dropping the run circuit (coil supply) to protect the motors, and its trip a-contact (pin 5) closes, firing the FR alarm above.

5. Wiring order — the fast way through

1. Main circuit first — MCCB → EOCR → MC → motor. Keep the colors (brown/black/gray) and run the heavy trunk first.
2. Control power → self-hold — tap control power off F and complete the start / self-hold / stop line on relay X.
3. Add conditions — splice SS, FLS, and T into the self-hold line.
4. Add results — drive the MCs, FR → YL·BZ, and the RL·GL indicators.
5. Field wiring — bring everything out through TB5·TB6 to the operator devices and motors, with conduit ①②③ and the octagonal box per the drawing.

Common mistakes — what fails you

• Wiring stop (PB0) as an a-contact → stop must be a b-contact (NC) in series. An a-contact won't stop the motor.
• Three wires on one terminal → instant fail. Two wires max per terminal; route the third via a pass-through (경유) terminal. → Terminal wiring rules
• Mixing wire colors → main L1·L2·L3 are brown/black/gray, earth is green, control is yellow. Mixing colors loses points.
• Ignoring conduit numbers → ①②③ specify the conduit *type*. Don't swap a cable run for conduit.
• Skipping the octagonal box → wherever conduit branches, it must pass through the octagonal junction box.

Next

Once the panel wiring is done, the last job is the conduit out to the field — Conduit finishing: pipe, saddles, and pulling wires. It covers how to do step 5 above (field wiring) to spec.

Try it yourself

A drawing alone feels abstract; wiring it one conductor at a time is how the circuit sticks.

Wire Public Problem 1 in the simulator →