A distribution box is assembled according to specific electrical wiring standards. It includes switchgear, measuring instruments, protective devices, and auxiliary equipment installed in a closed or semi-closed metal cabinet or on a panel, forming a low-voltage power distribution system. During normal operation, the circuit can be manually or automatically switched on or off. In case of malfunction or abnormal conditions, the protective device will cut off the circuit or trigger an alarm. The measuring instruments monitor various operational parameters and can also adjust certain electrical values to indicate or signal when the system deviates from its normal state.
During the installation of electrical systems, wires need to be connected to equipment, control switches, and distribution boxes. Depending on the cross-sectional size of the wire, smaller gauge wires are typically single-core, such as BV-3*2.5 (copper core with plastic insulation, consisting of three single-core wires). When these wires are connected to a distribution box, their insulation can be stripped and directly crimped into the box without the need for a terminal, often referred to as "terminalless external wiring." However, for smaller gauge multi-strand wires like flexible cables (BVR), which consist of multiple thin copper strands, it is common to use a metal sleeve—known as a "wire nose" or terminal—to secure the connection. This is called "terminal external wiring."
For larger cross-sectional wires, which are usually multi-stranded, terminals must be made. These terminals come in copper or aluminum types, depending on the wire material. The terminal material should match that of the wire—copper for copper conductors and aluminum for aluminum ones. This process is commonly referred to as "welding (or pressure) terminal blocks" in budget terms.
Based on the current budget quota subheadings, we can summarize the following rules:
1. For single-core conductors with a cross-sectional area less than 6 mm², terminalless external wiring is applied. If the cross-section exceeds 6 mm², it is considered large, and welding (or pressure) terminals are used instead.
2. For multi-core wires with a cross-section under 6 mm², terminal external wiring is applied. When the cross-section exceeds 6 mm², it is classified as large, and welding (or pressure) terminals are required.
3. The terminal material must always match the wire material—copper terminals for copper wires, and aluminum terminals for aluminum wires.
4. Once welding (or pressure) terminals are accounted for in the budget, the cost for terminal external wiring should not be included again.
These guidelines help ensure accurate and efficient electrical installations while maintaining compliance with standard practices and budgeting requirements.
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