A suitable surge protector (SPD) is an important technical task that directly relates to the safety of electrical equipment. Its core is to follow the principle of graded protection and match the key indicators based on installation location, protection requirements, and system parameters.
Below, I will use a table to outline the core steps and key parameters for selecting the surge protectors, and then explain in detail how to apply them.
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Selection Dimensionality |
Core parameters and selection criteria |
Application tips and common configurations |
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Determine the protection level (Type) |
Type 1 (T1, Level 1): To deal with direct lightning strikes, release huge energy, and the impact current (Iimp) is key. -Type 2 (T2, Level 2): Limiting induced lightning and operating overvoltage, nominal discharge current (In) is critical. -Type 3 (T3, Level 3): protects sensitive equipment ports and further reduces the residual voltage, which is usually installed in the front end of device.
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Graded configuration: Type 1 for the main incoming cabinet, Type 2 for the distribution box, and Type 3 for the front end of precision equipment. For the ordinary residential or low-risk scenarios, Type 2 is ok. |
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2. Key electrical parameters |
Maximum continuous operating voltage (Uc): It must be higher than the maximum normal operating voltage that the line may experience, taking into account factors such as harmonics. -Voltage protection level (Up): The residual voltage appearing at both ends of the equipment after the PD action must be lower than the withstand voltage value of the protected equipment. -Current carrying capacity(Iimp/In/Imax): reflects the ability of SPD to discharge surge current, which needs to be selected according to the installation location and lightning risk |
Uc: In 220/380V systems, Uc ≥ 275V (single-phase) or Uc ≥ 385V (three-phase) is usually selected based on installation location and lightning risk. -Up: Following the principle of gradual decrease, the Up of the end device should be ≤ 1.0 kV. - Current capacity: Iimp for Type 1 is recommended to be ≥ 12.5 kA; In for Type 2 is recommended to be ≥ 20 kA. |
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3.System matching and installation |
protection mode and pole number: select according to the power supply system (such as TN-S, TT, IT) and phase number (single-phase/three-phase). -Backup protection: to prevent short circuit in case of SPD failure, a dedicated backup protector (SCB) or matching fuse/circuit breaker must be equipped. -Installation and grounding: the grounding wire should be as short as possible (recommended ≤ 0.5 meters) to reduce induced voltage |
Pole number: TN-S three-phase system commonly adopts the 4P products; TT system recommends to choose the products with N-PE protection module. -Backup protection: the specific rated current should refer to the recommended value of the SPD manufacturer. |
Select according to the application scenario
The protection focus varies in different places, and you can refer to the following suggestions for preliminary judgment:
·Building power supply and distribution system
·Main distribution cabinet: Install Type 1 SPD, recommended impulse current Iimp ≥ 12.5 kA~25 kA, Uc=385V.
·Floor distribution electrical box: Install Type 2 SPD, recommended nominal discharge current In ≥ 20 kA, Up ≤ 1.5 kV~2.0 kV.
·Precision equipment/computer room: in servers PLC, Install Type 3 SPD on the front-end of medical equipment and other devices, with a requirement of Up ≤ 1.0 kV.
·Industrial automation
·In addition to power protection at all levels, dedicated signal surge protectors must be used for signal and data lines (such as RS485, Ethernet). Its Uc and Up need to match the signal level.
·Photovoltaic and other new energy systems
·DC side (such as combiner box, inverter DC end): DC SPD must be selected, and its Uc needs to adapt to higher DC operating voltages (such as 1000V or 1500V).
·Communication side: The protection principles are the same as those of conventional AC distribution systems.
Key points for installation and maintenance
Proper installation and maintenance are key to ensuring the effective operation of SPD.
·Equipotential connection: All SPD grounding terminals must be reliably equipotential connected to the building's lightning protection grounding system.
·Wire specifications: The wires (phase wire, neutral wire, ground wire) connecting SPD should have sufficient cross-sectional area. Generally, it is recommended that the main wire be ≥ 10mm ² and the ground wire be ≥ 16mm ².
·Status monitoring: Select SPDs with status indicator windows (green/red) or remote signaling alarm interfaces for daily inspection and timely replacement of faulty modules. It is recommended to conduct an inspection before the thunderstorm season every year.
Summary and Reminder
In general, when selecting a surge protector, please remember the following steps:
1. Clarify the location and level: First, determine where the SPD should be installed in the system (main distribution box, distribution box, or equipment front end), and then decide whether to choose Type 1, Type 2, or Type 3.
2. Check the parameters for matching: Focus on Uc, Up, and current carrying capacity to ensure that they match the power grid conditions and equipment withstand voltage level.
3. System adaptation ensures safety: Select the correct protection mode and number of poles according to the power supply system, and be sure to configure appropriate backup protection devices for it.
4. Standardized installation is the foundation: strictly follow the specifications for construction, especially the grounding wire should be short and thick.