Korean Electrician Public Problem 1 — Full Wiring Walkthrough

Last updated: 2026-10-05 · 7 min read

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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 junction box specified for this example.
• 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-yellow. (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 NO contact is open at rest, so substituting it in the series stop position can prevent starting. Trace the complete path.
• 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-yellow, 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.

Open the practical project list →

Check your understanding

Question: If only automatic mode fails, should you replace the MC first?

Answer: When the manual path works, trace the selector automatic path and FLS conditions separately before blaming the output device.

Practice path and references

The practical project list may require sign-in. Create a project, choose a task and place the relevant components, then compare the contact/wiring paths explained here. The link does not preload a specific completed circuit.

Reference: Q-Net public-problem notice, 2025-08-04 edition, problem 14 pages 11-1 to 11-4 (work/wiring instructions) and 11-9 (component diagrams). Read the original for each task and any amendments. Site examples are distinct from general installation design requirements.

Check the operating modes separately

In automatic mode, inspect the M1 path with SS=A and the level-detection condition. In manual mode, start with SS=M and PB1, then compare M1/M2 before and after the timer. Check stopping when changing modes or pressing PB0 separately. Read the alternating YL/BZ overload alarm independently of normal running indicators.

Reference: problem 1, pages 11-7 to 11-9 in the Q-Net package linked above (circuit, operation and component diagrams). Problem 14 is not the source for problem 1 operation.