Why Wire Diameter Matters?

When a surge occurs, the connecting conductors serve as the path for discharging lightning current into the ground. Insufficient conductor gauge can lead to wire burnout, SPD failure, or even fire; conversely, a properly sized conductor ensures that surge current is rapidly and safely diverted to the ground. Conductor sizing is subject to specific requirements under national and industry standards and must not be determined arbitrarily.

Three Principles of SPD Selection

1. By protection level: Level 1 (main incoming line) > Level 2 (power distribution) > Level 3 (terminal) > Level 4 (precision equipment); the higher the level, the larger the conductor cross-section.

2. Based on discharge current: As the values of In, Imax, and Iimp increase, the wire gauge must be increased accordingly.

3.  By material and length: Prioritize copper-core conductors; arrange connecting wires to be short and straight, with a total length of ≤0.5 m and secure fastening.

Requirements for conductor diameters of various sizes (copper core)

1. GB 50343 "Technical Code for Protection of Building Electronic Information System against Lightning"

2. GB 50343-2012 Technical Code for Protection against Lightning of Electronic Information System in Buildings

 3. DL/T 5408-2009 Code for Configuration, Installation, and Acceptance of 220/380V Power Supply Surge Protection for Electronic Information Systems in Power Plants and Substations

Note: For combined SPDs, select the cross-sectional area based on the corresponding protection level.

Practical Points

1.The ground wire is one size larger than the phase wire: the cross-sectional area of the protective ground wire is equal to or greater than that of the phase wire, ensuring priority for current discharge.

2. Upgraded Wire Gauge for Extended Lengths: For every additional 0.5m of cable length, the wire gauge is stepped up by one size to compensate for impedance.

3. Standardized copper-core insulated wiring: The use of aluminum wire or mixed copper-aluminum connections is strictly prohibited to prevent oxidation and overheating.

4. Secure crimping: Terminals must be crimped or tinned to prevent localized overheating caused by poor connections.

Summary

The key to selecting SPD wire gauge lies in: matching the protection stage, choosing copper conductors, keeping connections short, and ensuring a thick ground wire. Simply adhere to national standards, match the technical parameters, and ensure proper installation; there is no need to blindly pursue the thickest possible wire.