Introduction to the Functions of Primary Distribution Cabinet

The primary distribution cabinet on construction sites (referred to as "primary cabinet" for short), also known as the main distribution box, is the "heart" of the temporary electrical system at construction sites.

Functions and Roles

As the main entry point of the entire power distribution system at the construction site, the primary cabinet receives electrical energy directly from a transformer or an external power source, and is responsible for distributing and controlling it throughout the site. Its core functions can be summarized as follows:

Power Access and Master Control: Acting as the "main switch" for the construction site’s power supply, it connects to external high-voltage or low-voltage power sources and serves as the starting point for electricity use across the entire site.
Electrical Energy Distribution: Through internal busbars and outgoing switches, it distributes electrical energy reasonably to multiple downstream secondary distribution boxes (distribution boxes), providing independent power circuits for different areas and various large-scale equipment (such as tower cranes, construction elevators, and large processing yards).
Total Isolation and Total Protection: Equipped with a main isolation switch and a main circuit breaker, it facilitates the on-off operation of the entire site’s electrical circuits. In the event of serious faults (e.g., short circuits, severe overloads), it can quickly cut off the main power supply to prevent the escalation of accidents.
Metering and Monitoring: It is usually installed with electricity meters, voltmeters, ammeters, etc., which are used to monitor the total electricity consumption, voltage, and current conditions of the entire site, providing a basis for electricity management and cost accounting.
Primary Protection: It provides the most basic and critical leakage protection. In accordance with specifications, the leakage protector of the primary cabinet mainly functions as a fire prevention measure. It has a relatively large leakage action current (usually 150mA-300mA) and a slightly longer action time (e.g., 0.2s-0.3s). Its purpose is to prevent electrical fires caused by line insulation damage and form a hierarchical protection system with lower-level protection devices.

Advantages

Using standardized and qualified primary distribution cabinets brings significant benefits to construction sites:

High Safety

Enhanced operational safety: The main isolation switch ensures safe power cutoff for the entire area, facilitating maintenance and overhaul work. The cabinet itself also has a certain protection level, which can resist the impact of the external environment.
Centralized control: By controlling the site’s power supply through a single central point, it enables quick power cutoff in emergency situations, greatly improving emergency response capabilities.
Standardized wiring: With a clear internal structure and standardized wiring, it effectively reduces the risk of electric shock and short circuits caused by disorderly cable routing and connection.

Convenient Management

Easy metering: Centrally installed electricity meters make it convenient to count total electricity consumption and manage costs.
Easy maintenance: Its neat structure and clear labels facilitate daily inspections, maintenance, and troubleshooting by electricians.
Clear responsibility assignment: As the main power supply point, it clarifies management responsibilities, and its operation and maintenance are usually undertaken by full-time electricians.

High Reliability

Stable power supply: It adopts high-quality components such as circuit breakers and isolation switches, which can withstand large current impacts and ensure stable power supply to the entire site.
Strong adaptability: Its professional design allows it to adapt to harsh construction site environments (e.g., dust, temperature differences, vibrations) with a high protection level (e.g., IP54), providing dustproof and waterproof performance.

Compliance with Regulations

It is designed and installed in accordance with national standards such as Technical Specification for Temporary Electrical Safety at Construction Sites (JGJ46-2005), and is a necessary condition for construction sites to pass safety inspections and meet the standards for civilized construction.

Application Scenarios (Main Usage Occasions)

The primary distribution cabinet is an essential facility for all medium and large-scale construction sites, with clear application scenarios:

All construction sites: Whether it is housing construction, municipal engineering, road and bridge projects, or water conservancy projects, a primary distribution cabinet must be installed if temporary electricity is used.
As a main distribution center: Suitable for scenarios where power needs to be supplied simultaneously to multiple independent construction areas and multiple large-scale equipment.
It leads out independent power circuits to the living area, office area, steel processing area, tower cranes, construction elevators, concrete pump trucks, etc., respectively.
Used in conjunction with lower-level distribution boxes: The primary cabinet must never supply power directly to end-use electrical equipment (e.g., handheld power tools, lighting fixtures). Its downstream must be connected to secondary distribution boxes, which then distribute power to tertiary boxes (switch boxes) before finally connecting to the equipment.

In simple terms, the primary distribution cabinet on a construction site is the "first line of defense" for electrical safety and the "general headquarters" for energy management at the construction site. Its standardized installation and stable operation are the foundation for ensuring the smooth and safe progress of the entire project.

Widely used in various scenarios