It's quite common for certain regulations to be overlooked during the installation of electrical wiring, and many misunderstandings exist around these rules. Since the specifications don't always clarify every detail, I’ll share some real-world experiences from my own projects to help clarify the situation.
1. The color of phase lines should be yellow, green, and red. For example, in a three-phase building, when power is introduced into a three-phase meter box, the phase wires must be yellow, green, and red. When a single-phase power source is used, the same colors are still required. However, the three-core cable that connects the single-phase meter box to the household distribution box doesn’t necessarily need to match the incoming line’s color. This only applies if the user is using a three-phase meter box. In such cases, the outgoing wires should match the incoming ones. For buildings with 2–4 rooms, the phase wire can be any of yellow, green, or red. GB50258-96 requires that multi-phase wires be clearly distinguishable. For instance, if a 2-room unit has a red phase wire on its single-phase meter, an electrician can easily check if the red line is live using a voltage tester.
2. The neutral line should be light blue. This means that when possible, light blue should be the preferred color. In some countries, white is used instead. If the building uses white for all neutral lines, then all neutrals should be white. If dark blue is used for the neutral wire, the phase wires shouldn’t be green, as it’s hard to tell the difference in low light. For single-phase systems, the phase wire should be either red or yellow.
3. The protective earth (PE) wire must be yellow-green. This means that under normal circumstances, you must use yellow-green insulated cables for grounding. This helps ensure clear identification and safety.
4. When ordering cables or sheathed wires, the color must be specified. In practice, we often find that the actual color doesn’t match the requirement. For example, some projects use the same color for all three phase wires in a three-phase lighting cable, or use yellow, green, and red in a single-phase three-core cable—both of which are not allowed. Also, wrapping ribbons around wires is not a valid solution. Therefore, when ordering cables or sheathed wires, it's important to specify both the cross-section and the color, in addition to the model number.
By following these guidelines, you can avoid common mistakes and ensure safe, compliant electrical installations. Always double-check the color codes and specifications before proceeding with any project.
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