Standardize The Wiring Of Distribution Boxes

Wiring in distribution boxes involves a series of national standards and industry specifications. In actual construction, these national standards must be strictly followed to ensure the safety and reliability of electrical engineering.

I. Basic Wiring Requirements

1. Neat and Standardized Wiring

Wiring inside the box should be neat and free of twisted joints. Wire connections should be tight, without damaging the wire core or breaking strands. The cross-sectional area of ​​the wires pressed on both sides of the screw under the washer should be the same. No more than two wires should be connected to the same electrical component terminal. Anti-loosening washers and other parts should be complete.

Each electrical component connection point is allowed a maximum of two wires. Generally, two wires should not be connected to each terminal connection point. In special cases where two wires must be connected, the connection must be reliable.

2. No Joints in the Middle of Wires

There should be no joints in the middle of any connecting wires. Wire branch joints should not be bolted; they should be welded and insulated, with no exposed live parts.

3. Wire End Treatment

The stripped wire should not damage the wire core excessively. Wire crimping should be firm and reliable. Multi-strand wires should not be coiled and crimped; crimping terminals should be installed. If crimping with a set screw is necessary, multi-strand wires should be tinned before crimping; the number of strands must not be reduced.

4. Wire Color Marking

The color markings of wires within the distribution box must be strictly differentiated. Under no circumstances should color markings be mixed or substituted.

The insulation colors of all types of wires within the same building or structure should be consistent. In a single-phase 220V system, the live wire should preferably be red, the neutral wire blue, and the ground wire yellow-green. 

II. Wiring Procedure Specifications

1. N and PE Wire Configuration
The electrical mounting plate of the distribution box must have separate N and PE terminal blocks.

The N terminal block must be insulated from the metal electrical mounting plate, and the PE terminal block must be electrically connected to the metal electrical mounting plate.

The N wire in the incoming and outgoing lines must be connected through the N terminal block, and the PE wire must be connected through the PE terminal block.

Mixing of N and PE wires is strictly prohibited.

The N and PE wires must be routed out through separate busbars and must not be twisted together.

2. Different Circuits Must Not Share the Same Terminal
The N or PE wires of different circuits should not be connected to the same hole or terminal on the busbar. The same terminal on the busbar should not be connected to the N or PE wires of different circuits.

3. Wiring Point Requirements

The number of wiring points on the N-line terminal block and PE-line terminal block of the main distribution box (cabinet) should be n+1 (n-the number of circuits in the distribution box); the number of wiring points on the N-line terminal block and PE-line terminal block of the sub-distribution box should be at least two; the switch box should be equipped with N-line terminals and PE-line terminals.