- Home
- Product
- Fuse
- Electrical Protection
- Fuse Holder and Fuse Base
- Copper Busbar
- PV System
- Busbar System
- Electric Meter Box
- Power Distribution Box
- Blog
- Projects
- Resource
- Solutions
- About Us
- Contact Us
- VR Visit
Before choosing an SPD, identify the source of potential surges and the equipment that needs protection. Transient overvoltages may result from lightning-related events, switching operations, or disturbances entering through connected power and signal lines.
A low-voltage distribution system may require protection at more than one point. The main distribution board, downstream distribution panels, and sensitive equipment may have different protection requirements.
For example, an SPD installed at the incoming distribution board helps limit surges entering the installation. Additional protection closer to sensitive equipment may be necessary when the installation design and equipment requirements justify it.
Surge protection devices are commonly classified by their intended application and the tests they are designed to meet. The appropriate type depends on the installation, not simply on which product has the largest numerical rating.
| SPD Type | Typical Application | Selection Consideration |
|---|---|---|
| Type 1 | Installations where partial lightning current may enter the electrical system | Check whether the installation requires a lightning-current-tested SPD and the applicable impulse-current rating. |
| Type 2 | Distribution boards providing protection against induced lightning surges and switching overvoltages | Evaluate nominal discharge current, maximum discharge current where applicable, and voltage protection level. |
| Type 3 | Additional protection close to sensitive equipment | Check the required coordination with upstream SPDs and the equipment’s withstand characteristics. |
Some products combine multiple protection functions. Always verify the manufacturer’s declared classification, test requirements, and installation instructions instead of assuming that all SPDs of a particular appearance provide the same protection.
Uc is the maximum voltage that can be continuously applied to the SPD under the conditions specified by its manufacturer. It must be selected according to the system’s nominal voltage, voltage tolerance, earthing arrangement, and the connection mode used by the SPD.
Choosing Uc too low may cause unwanted operation or premature degradation. Choosing it without considering the system configuration may also leave the installation with an unsuitable protection arrangement.
Up indicates the declared voltage protection level of the SPD under specified test conditions. A lower Up can be beneficial, but it does not automatically guarantee better protection in every installation.
The actual voltage appearing at the protected equipment can also be influenced by connecting-lead inductance, wiring layout, and the distance between the SPD and the equipment.
Different SPD classifications use different current ratings and test waveforms. For example, Type 1 selection commonly involves the impulse current rating, while Type 2 selection includes nominal discharge current and may also specify maximum discharge current.
These values are not interchangeable. Compare the ratings using the applicable product standard and test conditions rather than choosing an SPD solely because it has the highest advertised current value.
The required SPD configuration depends on whether the installation uses a TN, TT, or IT earthing system and on how the SPD is connected between line, neutral, and protective earth.
The maximum continuous operating voltage and protection mode must be appropriate for the voltage that can occur across each connected SPD element under normal and fault conditions.
Before selecting a device, confirm:
For IT systems and other installations with unusual operating conditions, selection requires particular attention to the voltage that may appear between conductors during a first earth fault or another abnormal condition.
An SPD is not a substitute for the installation’s ordinary overcurrent protection. Depending on its design and the manufacturer’s instructions, an SPD may require a specified backup fuse or circuit breaker to protect fault or end-of-life conditions.
When reviewing backup protection, check the manufacturer’s maximum permitted backup protection rating, the prospective short-circuit current at the installation point, and the required coordination with the upstream protective device.
Do not select a backup fuse or circuit breaker using its rated current alone. Its breaking capacity and compatibility with the SPD must also be verified against the actual installation conditions.
Correct surge protection installation is essential to achieving the intended protection level. Even a correctly selected SPD can provide less effective protection if its connecting conductors are unnecessarily long or its wiring arrangement introduces excessive inductance.
During installation planning, consider:
The installation method should follow the applicable electrical regulations and the SPD manufacturer’s documentation. Requirements vary with the installation type, system configuration, and governing standard.
| Common Mistake | Why It Matters | What to Check |
|---|---|---|
| Selecting by discharge current alone | Current rating alone does not establish compatibility with the system or adequate protection for the equipment. | SPD type, Uc, Up, connection mode, and applicable test ratings. |
| Ignoring the earthing arrangement | The voltage across SPD elements can differ between system configurations. | System topology and the manufacturer’s permitted connection arrangements. |
| Using long connecting leads | Additional inductive voltage can reduce the effective protection achieved at the equipment. | Lead length, routing, and the installation instructions. |
| Overlooking backup protection | An SPD may not be adequately protected against fault current or end-of-life failure. | Manufacturer requirements, prospective fault current, and coordination. |
| Installing only one SPD without assessing the whole system | Downstream equipment may need coordinated additional protection. | System layout, cable distances, and equipment withstand requirements. |
Before finalizing a surge protection device for a low-voltage distribution system, confirm the following information:
A well-selected SPD is part of a coordinated protection design rather than an isolated component. Confirming these factors early helps engineers choose a suitable device and reduces the risk of incorrect ratings or ineffective installation.
For industrial projects, the final selection should be verified against the system design, applicable standards, and the manufacturer’s technical documentation.
Optimized by Seraphinite Accelerator
