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In low-voltage power distribution design, the labeling and representation of surge protectors (SPD) and their dedicated protection devices are now quite standardized and uniform. Have you come across situations where it was required to specify the specifications of the surge protector connection wires? In other words, is it the designer’s responsibility to clearly specify the specifications of the connection wires for various surge protectors? Let’s provide a brief analysis on this matter. Specifications for surge protector connection wires: yunrun.com.cn/tech/3716.html. The \"Technical Code for Lightning Protection of Electronic Information Systems in Buildings\" GB50343-2012 stipulates as follows: 6.5.1 The installation of surge protectors on power supply lines shall comply with the following requirements: ① Surge protectors at various levels of the power supply lines should be installed at the points where the lines enter the building, at the boundary of the lightning protection area, and near the equipment that needs protection. The connection wires of surge protectors at all levels should be short and straight, with a length not exceeding 0.5 m, and they must be firmly fixed. The grounding terminal of the surge protector should be connected, over the shortest distance possible, to the equipotential grounding terminal board in the area affected by lightning. The protective earth wire (PE) of the distribution box shall be directly connected to the equipotential grounding terminal block. ②Surge protectors for power lines with terminals should be crimped ； Surge protectors equipped with terminals should preferably be connected using terminal blocks and terminals. ③The minimum cross-sectional area of the connection wires for surge protectors should comply with the requirements specified in Table 6.5.1. http://yunrun.com.cn/upload/202104/24/202104241544315152.png specifies the minimum cross-sectional area requirements for SPD connection wires, with the grounding wire requiring a larger gauge than the upper lead wire. According to the provisions of the Code for Design of Lightning Protection of Buildings GB 50057-2010: 5.1.2 The minimum cross-sectional area of each connection component in the lightning protection equipotential bonding system shall comply with the requirements specified in Table 5.1.2. The minimum cross-sectional area of a single conductor connecting one or more Class I rated experimental equipment or D1 type surge protectors shall be calculated using the following formula: Smin ≥ Iimp/8, where Smin represents the minimum cross-sectional area of the single conductor in mm2 ； Iimp is the lightning current (kA) flowing into that conductor. According to the table above, the minimum cross-sectional area for SPD connection wires is also specified; note that this is a minimum requirement, and it is lower than the minimum requirement set out in GB50343. Therefore, it should also be calculated according to Equation 5.1.2, based on the lightning current flowing into the SPD connection wires. And what is the actual lightning current flowing into a particular SPD? According to the analysis and calculations based on various standards and literature, this is closely related to factors such as the installation location of surge protectors (SPDs), the shunt coefficient at that location, as well as the number of conductors leading from the building and various connection pipes. If the calculation is inaccurate, it is recommended to select according to the accompanying manual: (6) The cross-sectional area of the connection wires and grounding wires for surge protectors. The upper lead wires and grounding wires of surge protectors are generally made of multi-strand copper wires. The minimum cross-sectional area of these connection conductors has been appropriately modified in GB50057-2010 with respect to the minimum area recommended by IEC standards. The requirements for the minimum cross-sectional area of the SPD connection conductors per phase, depending on whether they are connected to electrical or electronic systems and depending on the different test categories, are shown in Table 13.9.2. When connecting one or more Class I classified test surge protectors or D1 type surge protectors (such as the connection wires and grounding wires of the SPDs connected between the N-PE conductors in a “3+1” wiring configuration), the minimum cross-sectional area of each individual connection conductor shall be estimated using Equation (13.9-1), and the standard cross-sectional area closest to this calculated value shall be selected. Note: Given that various domestic and international technical standards impose different requirements on the cross-sectional area of the connection wires and grounding wires for surge protectors, and in the interest of safety as well as considering the low usage volume of such connection wires, it is advisable to choose a larger cross-sectional area for the wires ； The manual recommends referring to Table 13.11-19 for determination. The sections in Tables 13.11–15 are fairly safe, after all, the peak value of the lightning current for Category II lightning protection buildings is only 150 kA, provided that the parameters of each SPD surge protector are selected correctly. So, in the design drawings, is it necessary to indicate the specifications of the SPD surge protector connection wires? If it isn’t specified, does the manufacturer resolve this issue accurately on their own? Source: Changhui Instrument Network Author: Design Mentorship