Selection of copper bar for power distribution cabinet

In communication and power cabinets, the selection and calculation of DC and AC grounding copper bars and busbars are crucial. These components are essential for ensuring system safety, reliability, and optimal equipment performance. This article provides a detailed guide on how to calculate and choose the appropriate grounding copper bars and busbars.

I. Importance of Grounding Copper Bars

Grounding copper bars are used to connect the electrical components of equipment to the ground, preventing damage due to unstable voltage or external interference. A good grounding design can effectively prevent electric shock accidents and ensure the normal operation of equipment. In communication and power cabinets, grounding copper bars form the foundation for electrical safety.

II. Importance of Busbars

Busbars are used to consolidate the currents from multiple circuits for centralized management and distribution of electrical load. They are commonly used in DC distribution systems and power transmission systems to ensure that current is safely and effectively transmitted to various devices.

III. Selection of DC and AC Grounding Copper Bars

1. Material Selection

Copper bars are typically made of high-conductivity copper, which has low resistivity and can effectively reduce power loss. For harsh environments, tinned copper bars should be considered for their improved corrosion resistance.

2. Cross-sectional Area Calculation

The cross-sectional area of a grounding copper bar determines its current-carrying capacity and is usually calculated using the following formula:

• A is the cross-sectional area of the copper bar in square millimeters (mm²).
• I is the maximum current flowing through the copper bar in amperes (A).
• J is the allowable current density in amperes per square millimeter (A/mm²), typically ranging from 1.6 to 2.5 A/mm².

For example, if the maximum current in a DC system is 500A and the allowable current density is chosen to be 2A/mm², then the cross-sectional area of the copper bar should be at least 250mm².

3. Temperature Rise Coefficient

When selecting a copper bar, the temperature rise coefficient must also be considered. This coefficient indicates how much the temperature of the copper bar will increase due to the heat generated when current passes through it. The temperature rise coefficient is usually provided by the manufacturer, and the copper bar should be chosen based on the operating environment and temperature requirements.

IV. Selection of Busbars

1. Load Calculation

Busbars must carry the total current load from multiple circuits, so the calculation must consider the sum of the maximum load currents of all circuits. The busbar size should satisfy:

• ∑I is the total current of all circuits in amperes (A).
• J is the allowable current density.

If the busbar needs to carry a total current of 1000A, and the current density is 2A/mm², then the cross-sectional area should be at least 500mm².

2. Mechanical Strength

In addition to electrical performance, the busbar must have sufficient mechanical strength to support its installation and withstand mechanical stress over time. Choosing a busbar with a thicker and adequately wide design will provide better mechanical stability.

3. Thermal Design

In high-current scenarios, busbars generate significant heat. Therefore, thermal design is critical. Consider increasing the surface area of the busbar or adopting a design that enhances heat dissipation to ensure that the busbar does not overheat during high load operations.

V. Layout of Grounding and Busbars

The layout of copper bars is also important. Grounding copper bars should be positioned as close to the bottom of the cabinet as possible to quickly direct current to the ground. Busbars should be located near the power input of the equipment to facilitate current distribution and management.

VI. Comprehensive Selection Recommendations

In practical applications, the selection of grounding and busbars should be based on specific current loads, equipment power, ambient temperature, and other relevant factors. Regular inspections and maintenance of copper bars are recommended to ensure good contact, and to check for corrosion or loosening.