Internal Structure of Distribution Box

The internal structure of the distribution box is designed to safely distribute power from the main power source to multiple branch circuits. It provides convenience for protection, control and maintenance. This article discusses the construction of the distribution box, its functional divisions, and selection tips. This article can help you better understand the internal structure of the distribution box, which benefits the safety, operational efficiency, and long-term lifespan of your system.

What Is a Distribution Box?

The distribution box can also be called a 배전반 or an electrical panel. It is a centralized electrical unit designed to house switches, protection and distribution components. Its internal structure guarantees controlled power distribution, overload and short-circuit protection, grounding, and the safe operation of electrical systems in residential, commercial and industrial applications.

The two key functions of the distribution box are power distribution and circuit protection. Power distribution involves safely distributing the main power to different circuits. This process mainly guarantees the safety and orderliness of your power system.

Besides, the distribution box also plays an important role in protecting your circuit system. Short circuit protection and overload protection are built-in protection mechanisms. These protection mechanisms can effectively prevent electrical faults that may damage the system or cause fires.

Internal Structure of a distribution box

Enclosure and Mounting Structure

The enclosure forms the shell of the distribution box. It can protect the internal components from mechanical damage, dust and accidental contact. Distribution boxes are usually made of metal or plastic.

Engineering plastics have good insulation, corrosion resistance and are lighter in weight, and are generally used as household distribution boxes. The metal enclosure(스테인리스 스틸 또는 아연 도금 강철) has high mechanical strength and good fire resistance. You can use metal distribution boxes in industrial, outdoor or heavy-duty environments.

Generally speaking, the enclosure also has a certain level of IP rating. You can choose a distribution box with a specific IP rating based on your installation environment to provide a protective, supporting and cooling environment for the internal components.

Busbars System

The bus bar is a conductive metal strip, usually made of copper or aluminum. It is used to distribute electricity from the main switch to multiple circuit breakers. Compared with traditional wiring methods, the busbar system has more reliable connections and lower contact resistance. It also reduces the messy wires inside the box and saves space in the distribution box. The bus bar also improves the efficiency of current distribution and reduces heat accumulation.

Circuit Protection Devices

The circuit protection devices in the distribution box mainly include 회로 차단기, residual current devices and fuses. The circuit breaker is a protective device that automatically cuts off the circuit when overload or short circuit occurs. Each outgoing circuit is usually equipped with an independent circuit breaker for independent protection. Common circuit breakers include miniature circuit breakers (MCB) and moulded case circuit breakers (MCCB).

Common residual current devices are RCD, RCCB, and RCOBO. They can prevent electric shocks and reduce the risk of fire. They detect residual current and cut off the circuit when the leakage current exceeds the safety limit.

The fuse works by using a metal fuse element to melt under excessive current, thereby providing circuit protection. Its breaking capacity is extremely high. You can use it in situations where there are extremely high requirements for short-circuit protection.

Main Switch and Incoming Terminals

The main switch can also be called the main isolator. It controls the entire power supply of the distribution box, which is the main point for electrical isolation. You can manually disconnect all outgoing circuits at once through the main switch to guarantee safety during maintenance or emergencies. The main switch is usually installed on the incoming side of the distribution box.

The isolator only provides physical isolation and does not provide overload or short circuit protection. It needs to be used in conjunction with the lower-level circuit breaker.

The incoming terminal block is the connection point where the external power cable enters the distribution box. These terminals are used to handle high currents. It can provide a safe and stable electrical connection between the power supply and the internal system.If the terminals are not properly connected, it may result in poor electrical performance of the distribution box and even cause electrical hazards.

Outgoing Circuits and Internal Wiring

Outgoing terminals connect internal wiring to external load circuits. They guarantee secure connections and help organize wiring for different electrical loads such as lighting, sockets, and equipment.

Internal wiring connects all components inside the distribution box. It must follow proper color coding, routing, and insulation requirements to guarantee safety, reliability, and easy maintenance.

Apart from the main components mentioned above, the distribution box for your application may also include surge protection devices (SPD), indicator lights, meters or monitoring devices, labels and identification tags.

Every component inside the distribution box plays a vital role in ensuring safe power distribution, fault protection, and system reliability. A well-designed internal structure can reduce the failure risk of the distribution box, improve its maintenance efficiency, and comply with electrical safety standards.

Functional Zoning Inside the Distribution Box

The internal space of the distribution box is divided into different areas according to the functions of the electrical appliances. This guarantees the safe flow of electricity, improves reliability, simplifies maintenance, and also helps to comply with electrical standards for the distribution system.

Power Input

The power input zone is mainly responsible for receiving, isolating and monitoring the electrical energy from the power grid or the upper-level distribution system. This area can safely connect and isolate the entire distribution system and serves as the starting point for internal power flow.

The main components in this area include incoming terminals, main switches or main circuit breakers, and surge protection devices. They are used to deal with the highest current level in the system. Most importantly, these components require strong insulation and secure connections. This zone is usually located at the top of the distribution box or near the cable entry points. It has relatively independent space, which is convenient for your operation and observation.

Protection and Control

The protection and control zone within the distribution box is mainly responsible for real-time monitoring, fault detection and line protection for all outgoing circuits.

This area can monitor the operating status of each branch circuit. In the event of overload, short circuit, leakage and other abnormalities, it can quickly and selectively cut off the faulty circuits to protect the safety of the lines and equipment, and minimize the scope of power outages to the greatest extent.

The main components of this area include circuit breakers, residual current protectors, timers, indicators and other auxiliary control devices. The protective device is usually installed in a modular way on the DIN rail, which is convenient for your identification and operation. Each protection device corresponds to a line circuit and is equipped with a clear label.

Power Distribution/Output

The power distribution zone inside the distribution box is mainly responsible for efficiently and reliably distributing electrical energy to various protection and control devices, and ultimately delivering it to the load. The collection and distribution of power is mainly achieved through the establishment of low-resistance and highly reliable internal conductive pathways.

The main components include the busbar, neutral busbar and ground(earth) busbar. They are mainly used for efficient current distribution. It can also reduce the complexity of wiring, but you need to leave sufficient spacing between the components and keep their insulation.

Safety and Maintenance Consideration

Grounding and safety zone can provide grounding and fault current paths to guarantee electrical safety. It can safely discharge fault current and enable the protection device to operate correctly to protect personnel and equipment. The main components include earth busbar, protective earth conductors, and bonding connections.

Heat dissipation and clearance zone manage the heat and keep a safe electrical clearance within the electrical distribution box. The main components in this area include ventilation openings and heat-resistant materials. They prevent overheating to support the stable and long-term operation of the distribution box and the load equipment. In the long run, good heat management can also extend the lifespan of the components.

Common Internal Structure Configuration

The internal structure configuration of a distribution box varies depending on power supply type, application environment, load capacity, and safety requirements. Understanding these configurations helps you in selecting, installing, and maintaining the correct distribution box for different use cases.

Single-phase Distribution Box

The internal configuration of the single-phase distribution box consists of one phase(L), one neutral(N), one earth(PE) wire, and a single-phase busbar system. It also has the main switch  and multiple MCBs for branch circuits, as well as for leakage protection with RCD or RCBO. The internal layout of the single-phase distribution box is compact, with fewer protective devices and a simple wiring path.

However, the installation and maintenance of single-phase distribution boxes are simpler. It has obvious cost-effectiveness for low-load applications. You can apply single-phase distribution boxes in residential buildings, small offices, stores, and light commercial systems.

Three-phase Distribution Box

The internal configuration of the three-phase distribution box includes three conductors(L1,L2,L3), neutral, and earth, as well as a three-phase busbar system. Besides, there is an MCCB or a high-capacity MCB serving as the main switch.

The cabinet size of the three-phase distribution box is larger, and the wiring and bus arrangement is more complex. The current rating components of the three-phase distribution box are also higher.

However, the three-phase distribution box supports heavy loads and also improves efficiency and system stability. Therefore, you can use it in industrial facilities, commercial buildings, and high-load systems.

Residential Distribution Box

The interior of a residential distribution box usually features single-phase or small three-phase inputs, used for RCBOs for individual circuits, and clear circuit labels. The design of residential distribution boxes pays more attention to the safety and convenience of use, with minimum access and maintenance. And it also needs to comply with residential electrical standards.

Industrial Distribution Box

Most industrial distribution boxes are applied in factories and plants, as well as heavy machinery environments. Therefore, the interior of industrial distribution boxes is equipped with a large number of MCCBs, heavy copper busbars, advanced grounding systems, and integrated control equipment. These devices all demonstrate the high fault-tolerance and mechanical strength characteristics of industrial distribution boxes. They are more suitable for long-term continuous operation.

Modular Distribution Box

The modular design of the distribution box is equipped with modular DIN rail installation components and adjustable busbar and wiring layouts. You can easily add and replace circuits in the modular electrical distribution box. The modular electrical distribution box supports customization, has high flexibility, and reduces downtime during upgrades.

Outdoor Distribution Box

Outdoor distribution boxes are usually equipped with rainproof enclosures to adapt to outdoor and harsh environments. Besides, the insulation and sealing of outdoor fiber distribution boxes need to be strengthened and equipped with corrosion-resistant components. For safety, outdoor distribution boxes also require additional grounding protection. You can easily tell that outdoor distribution boxes pay more attention to environmental protection, long-term durability, and safety under extreme conditions.

Factors to consider When you choosing distribution box

Consider Phase Type and Installation Environment

First, you need to consider the type of distribution box you choose according to your installation environment. Single-phase distribution boxes (220V) are suitable for the majority of residences and small shops. Three-phase distribution boxes are more suitable for larger-load factories and commercial premises. These are the parameters you need to confirm first.

Second, if it is used as a residential  distribution box, you need more attention to the personal safety, beautiful, operation convenience. For commercial distribution boxes, you need to focus on their system reliability, continuous operation, scalability, etc. For outdoor environments, you need to consider the protection level and the material’s anti-corrosion ability.

Size, Durability and Compliance

You need to determine the size and number of circuits for the distribution box based on the current number of electrical circuits, and reserve space for future expansion. Besides, the material of the distribution box should be selected according to the environment. Choosing a plastic distribution box or metal distribution box?

Similarly, the IP등급 of the distribution box is determined by the installation environment. Outdoor environments usually require IP65 or higher. Your installation method, whether it is open or concealed, needs to be determined in advance. You also need to verify whether the distribution box complies with local or international standards and regulations such as IEC, CE, and UL.

Besides the above factors, you also need to consider whether the distribution box has an independent and reliable protective grounding terminal. If you are concerned about maintainability and scalability, you can choose a modular distribution box and reserve sufficient space. If necessary, you can also choose a smart distribution box, which can provide you with more efficient management.

자주 묻는 질문

How is Internal Wiring Organized Inside a Distribution Box?

Internal wiring is arranged using structured routing, cable ties, wire ducts, and clear separation of phase, neutral, and earth conductors to prevent interference and improve safety.

What Safety Features are Included in the Internal Structure of a Distribution Box?

Safety features include insulation barriers, proper clearance distances, grounding systems, protective devices, flame-retardant materials, and secure fixing of internal components.

Will the Internal Spacing and Gaps Affect the Safety of the Distribution Box?

Yes. A well-designed internal structure guarantees stable power distribution, minimizes faults, improves heat management, and extends the service life of the system.

Final Thought

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