Solving the "terminal block problem" where single-phase 100V and power 200V coexist at once

Published problem 4 is a slightly unique problem that is said to be ``difficulty level 4/5'' in the second class electrician skill examination. (Electric Shop Peko, 2023) (Electric Shop Peko)
The reason is very simple: "single-phase 100V circuit" and "power 200V circuit" appear at the same time, and "terminal block", "designation of electrical materials for joints", and "confirmation indicator light" are also involved. (Electricist Peco)

In this article, based on the explanations provided by HOZAN, Denkiya Peko, and Gamidenki Channel, we will organize the construction to a very detailed level so that even beginners can follow the construction steps on this page.

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Basic information

• Test time: 40 minutes (In the video, the installation is shown in about 10 minutes, but during the actual test, it is recommended that you take the test calmly and use the full 40 minutes.) (Deki-ya Peko, 2023) (Deki-ya Peko)
• What is the theme of this exam number?
  • Circuit configuration with a mix of single-phase 100V and power 200V circuits
  • Concept of expressing hardwired circuit breakers, earth leakage circuit breakers, and installation terminals together using a terminal block Gamidenki channel
  • Joint part where different connection parts (insertion type connector/ring sleeve) are specified for the left and right sides (Electric shop Peko)
  • Understanding how to connect the confirmation indicator light (pilot light)

If you can overcome this problem,
"Wiring similar to practical wiring that mixes single-phase and power"
"Terminal block look"
"Color-coding/switching wire size"
You will quickly acquire such applied skills.

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Tools needed for this exam

In addition to basic tools, there are many terminal blocks and ring sleeves, so it is important to ``peel the coating quickly in a certain length'' and ``imprint crimp marks accurately.''

• Crimping pliers (for ring sleeves: able to reliably crimp small and medium sizes)
• va stripper
  • It is advantageous to have a type that allows you to quickly peel off the VVF1.6/2.0 exterior and core wire coating to a fixed length. The video also strongly recommends the dedicated VA stripper (Denki-ya Peko, 2023)
• Phillips screwdriver (for terminal blocks, switches, and outlets)
• Nippers/pliers (terminal shaping/light bending/cutting)
• Measure or ruler (measuring cable length)
• Electrical knife (for fine sheath processing/fine adjustment)
• Passed multi-tool with integrated cable stripper (HOZAN)
  • Example: A type with a scale that allows you to peel off the sheath while measuring the length.
  • A type that can perform crimping, cutting, and stripping in one piece.

On the actual question paper, the ``distance between cores'' of each cable is indicated in dimensions such as 100 mm, 150 mm, and 200 mm. On the other hand, the idea is to cut the cable by adding the length that will fit inside the device or the length required for the joint (Electrical Shop Peko, 2023).

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Materials to be prepared for this exam

In the actual published problem 4, the "type" and "length" of cables are provided quite differently. (Electricist Peco)

In HOZAN's explanation, typical supplied cables are introduced as follows. Hozan 2adfdf85234680e38acfcaec1…

• VVF 1.6mm 2-core (black/white)…approx. 1.5m
• VVF 1.6mm 3 cores (black, white, red)…approx. 0.5m
• VVF 2.0mm 3 cores (black, red, green, etc.)…approx. 0.5m (used on the power 200V side)

Typical equipment and components include:

• Terminal block (6 terminals)
  • Used to collectively express hardwired circuit breakers, earth leakage circuit breakers, and installation terminals.
• Lamp receptacle (without cover)
• Hanging ceiling (square or round)
• Embedded tumbler switch
• Embedded continuous outlet (with installation pole)
• Embedded mounting frame (frame for attaching switches and outlets)
• Joint box (including parts extending to omitted parts)
• Ring sleeves (several pieces, mainly small ones)
• Plug-in connector (for 2 or 3 wires)

The construction conditions clearly specify the connection materials: a plug-in connector for the left joint and a ring sleeve for the right joint. (Electric Shop Peko, 2023)

If you make a mistake in this specification, you will be immediately disqualified, so be sure to draw a marker on the bold part of the construction conditions on the question paper. (Electric Shop Peko, 2023)

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Main flow

From here, we will organize the flow from the signal to start the exam to the confirmation of completion, keeping in mind "time allocation" and "when to use the HOZAN passing multi-tool."

1. Loading construction conditions (2 to 3 minutes)
2. Confirmation of supplied materials (2-3 minutes)
3. Equipment placement and joint box preparation (5 minutes)
4. Measuring and cutting cable length (8-10 minutes)
5. Wiring to terminal blocks, switches, outlets, and lighting equipment (15 to 18 minutes)
6. Connecting the joint (plug-in connector/ring sleeve) (5 minutes)
7. Final shaping and defect checking (all remaining time)

1. Loading construction conditions

• Handling the terminal block
  At the bottom of the wiring diagram, an overview of the molded circuit breaker, earth leakage circuit breaker, and installed terminals is shown as the "internal configuration of the terminal block." (Hozan, Explanation of Publication Question 4)
  First, understand which terminal is R/S/T (or 100V L/N) and which terminal is installation.
• How to connect the confirmation indicator light
  Construction condition number 3 tells you which phase and which line to use to light up. (Electric Shop Peko, 2023)
• Specification of joint parts
  Left joint: Plug-in connector
  Right joint part: ring sleeve
  Be sure to check the specification. (Electric Shop Peko, 2023)

If you roughly draw in your mind "which cable is on the 100V side," "which cable is on the 200V side," and "where it extends from the terminal block," it will be easier to draw the double-line diagram later.

2. Confirmation of supplied materials

• Does the number and length of cables match the drawing?
• Number of terminal blocks, switches, outlets, mounting frames, ring sleeves, and plug-in connectors

If the quantity is insufficient, please inform the examiner at this time. (Electric Shop Peko, 2023)

If you roughly measure the length of the cable using a HOZAN certified multi-tool scale with memory, it will be easier to decide which cable to use for which section.

3. Placement of equipment and preparation of joint box

• Arrange the equipment on the board according to the wiring diagram. (Gamidenki, commentary on public issues)
• Attach the mounting frame to the outlet (or the appliance specified in the installation conditions) with the "Top" indication facing upward.
• If you have a joint box, also install the rubber bushing at this stage. Gamidenki channel

Now take a deep breath and decide where to start pulling the cable. It's up to you whether you start with 200V or 100V of power first, but Gamidenki Channel recommends ``wiring from the power supply section first''. Gamidenki channel

4. Measuring and cutting cable length (HOZAN multi-tool useful point)

This is where the HOZAN certified multi-tool comes into play.

• Cut the cable while measuring the distance between the devices + extra length (approximately 5 to 10 cm) using the scale engraved on the multitool.
• Stripping the sheath of the cable that goes into the terminal block by about 5 cm, and stripping the core wire by about 12 to 15 mm, will make it easier to securely tighten the terminal screws. (Gamidenki, terminal block explanation)

If your multi-tool has a VA stripper function, you can switch the dial between 1.6 and 2.0 to quickly peel off a certain length, which will save you a lot of time.

5. Connection to terminal block/equipment

200V (power) side

The Gamidenki channel introduces an example of starting construction from the 200V side.

• Cable used: VVF2.0mm 3-core (black, red, green)
• The bottom of the terminal block is the installation terminal, so insert the green wire there.
• Since the top two are 200V phases, add black and red optionally (refer to construction conditions for R/S assignment)

HOZAN's explanation introduces an example where the construction conditions specify that "R phase = red, S phase = white, T phase = black" for 200V three-phase R, S, and T.
The color scheme may be slightly different in Published Question 4, but "color-coding by phase" is always written in the conditions, so be sure to match it accordingly.

100V side

• Uses VVF1.6mm 2-core (black/white)
• Black = non-grounded side (L), white = grounded side (N)
• Always follow the rule of putting white on the N side (W terminal) of lamps, outlets, and switches. (Electrical shop Peko, explanation of published questions 1 and 2)

If you connect the black wire from the power supply (or the black crossover wire from another device) to the switch's No. 0 terminal, the entire circuit will be unified and it will be easier to check later. (Gamidenki channel)

Confirmation indicator light (pilot light)

• The construction conditions will specify whether the lighting is a combination of 200V single-phase and 100V neutral wires, or lighting only on the 100V side. (Electrical shop Peko, Published problem 4 explanation)
• When drawing a double-line diagram, it is important to organize in advance "which phase to start with and which line to return to."

6. Connection of joint part

• Left joint: Plug-in connector
  • Construction conditions specify that plug-in connectors should be used in places where there are four IV wires, etc. (Electricist Peko, Explanation of Published Problems 4 and 5)
• Right joint part: ring sleeve
  • Crimp the parts where 2 to 3 wires are connected using a ring sleeve.

Crimping pliers have markings such as "small" and "medium", and the markings change depending on the thickness and number of wires used.
If you have small ring sleeves + 3 VVF1.6 pieces, you will be able to get used to the construction conditions and practice, such as stamping "○", so you won't get confused during the actual installation.

Here again, if you have a HOZAN-approved multi-tool with a crimping function, you will reduce the number of times you have to change pliers and save time.

7. Final shaping and defect checking

• Have you forgotten to tighten the terminal screws?
• Is the sheath removed too much? (Does the sheath remain at least inside the joint box?)
• Is the copper of the core wire too exposed (within 2 to 3 mm as a guide)?
• Will the switch/outlet fall off from the mounting frame? (Gamidenki channel)
• Is the ground wire (green) properly connected to the ground terminal of the terminal block or outlet?

If you can spend more than 5 minutes on this final check, your passing rate will increase considerably.

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How to draw wiring diagrams and things to be careful about

The trick to thinking about double-line diagrams is to separate "single-phase 100V" and "power 200V".

Step 1: Take a picture of the equipment and power source

On the Gamidenki channel, we start by drawing the equipment according to the wiring diagram. '(Gamidenki channel)

• Power supply section (terminal block)
• switch
• outlet
• Lighting (lamp receptacle/hook ceiling)
• joint box

Copy it down, keeping in mind the positional relationship.

Step 2: Tie the N side (ground side) first

• Connect the N side (white) of the 100V circuit to the N terminal of the lamp, outlet, etc. all at once.
• Since there is no neutral wire on the 200V side, we will consider it separately as a "200V block".

Step 3: Write the power 200V block

In HOZAN's double line diagram explanation, the color coding for 200V three-phase R/S/T is specified.

• R phase: red
• S phase: white (or specified color)
• T phase: black

In published problem 4, configure 200V with VVF2.0-3 cores (black, red, green), and connect the green wire to the bottom of the terminal block as an installation wire. (Gamidenki, commentary on the 4th series of published questions)

On the double line diagram,
"Draw in color between R/S/T or L1/L2 of the terminal block and the power load (motor or indicator light)"
Organizing it with images makes it easier to see.

Step 4: Specify the wiring of the confirmation indicator light

Make a note of the construction condition, ``The confirmation indicator light must display the status of 〇〇'' next to the double-track diagram. (Electric Shop Peko, 2023)

• Example: "Displays that voltage is coming to the power circuit"
  → Connect the lamp between one phase on the 200V side and the common line (neutral line or other phase)

Mistakes can be reduced by using visual techniques, such as making only the confirmation indicator light a thick line on a double-track diagram.

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How to proceed with practical skills and take a breather

Publication Question 4 contains a large amount of information, so it is extremely important to know where to take a breather and review the whole thing.

First half (~20 minutes): Time to make the shape

• Equipment arrangement
• cable cut
• Connection to terminal block/equipment

At this stage, the emphasis is on speed, and the shape is created all at once.
However, be careful with the terminal block and joints as they are difficult to redo later.

Middle part (20-30 minutes): Organizing joints and wiring

• Be careful not to confuse the "plug-in type connector" with the "ring sleeve" at the left and right joints (point to the diagram for installation conditions). (Electricist Peco)
• Double-check that the crimping marks (○, small, etc.) are correct by looking at the stamp on the HOZAN-approved multi-tool or crimping pliers.

At this point, I put down my tools, take a deep breath, and compare the double-track diagram with the real thing, visually checking to see if the number of lines, colors, and destinations match.

Second half (30-40 minutes): Defect finding mode

• Is the correct wire connected to the switch number 0 terminal? Gamidenki channel
• Is there a white line on the W side of the outlet?
• Is there a green wire in the terminal block installation terminal?
• Is the ring sleeve inside the joint box securely crimped?

If you allocate your time with the mindset that ``I won't do any new wiring for the last 10 minutes, and I'll just use it for checking,'' you can review things calmly.

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Items to check for defects and oversights

Finally, we will summarize the flaws that are said to be particularly common in Publication Question 4.

1. Incorrect phase sequence and installed terminals on the terminal block
   • The green wire is connected to a place other than the installation terminal.
   • The phase order of the 200V circuit is not assigned according to the construction conditions (violation of using red, white, and black) Hozan
2. Mixing up electrical materials in the joint part
   • In the left joint part, the original ring sleeve is replaced with a plug-in connector, or vice versa.
   • This is a mistake that is clearly stated in the construction conditions as ``immediate disqualification.''
3. Cable size mix-up
   • The 200V side uses 1.6mm even though 2.0mm is specified.
   • This can be prevented by first checking the thickness and length of the provided cable. Hozan
4. Incorrect wiring of confirmation indicator light
   • The lamp that originally monitors 200V is connected to 100V.
   • Conversely, even though the lamp has a 100V circuit, 200V is applied to it.
     → Make a large note of ``which voltage is displayed'' on the double-line diagram. (Electric Shop Peko, 2023)
5. Excessive stripping of sheath/coating, exposed copper wire
   • Copper wire protrudes more than 5 mm from the threaded part of an outlet or switch
   • Inside the joint box, there is almost no sheath left and the core wire is exposed.
     → As a general guideline, it is safe to leave 2 to 3 mm of exposed copper at device terminals and 5 to 10 mm of sheath at joints inside the box.
6. Falling of the mounting frame/equipment
   • The orientation of the mounting frame is reversed (the "top" display is below).
   • The outlet is not properly fixed to the frame and comes off when pulled.
7. Forgetting to wire the parts that were omitted during construction.
   • The Gamidenki channel also introduces ``forgetting to connect parts that were omitted during construction'' as a typical mistake. Gamidenki channel

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Summary and references

Publication question 4 is

• Mixed single phase 100V and power 200V
• Handling the terminal block
• Electrical material specification for joint parts
• Confirmation indicator light

This is a problem packed with practical elements.

It may seem difficult at first, but
"Organize the double line diagram by dividing it into 100V blocks and 200V blocks"
“Standardize the length and stripping with a HOZAN-approved multi-tool”
"The last 10 minutes are focused on finding defects."
If you keep these three things in mind, you can easily complete the process within 40 minutes.

Finally, I would like to list the videos and materials I used as reference for this content.

• Electrician Peko “Class 2 Electrician Skills Exam Publication Question 4 Explanation Video” (2023 Candidate Question 4)
• HOZAN “Class 2 Electrician Skills Exam Publication Question 4 Explanation Video” (Explanation of terminal block and cable supply conditions)
• Gamidenki Channel “Class 2 Electrician Publication Problem Series” (Concept of terminal blocks and how to draw double-line diagrams)