Surge Protection Devices (SPD) in Custom Engineered Panel

The correct SPD type depends on the panel location and exposure. Type 1 SPDs are used at the service entrance when the installation is exposed to direct lightning current or has an external lightning protection system. Type 2 SPDs are the standard choice for distribution and sub-distribution panels under IEC 61643-11, especially in IEC 61439-2 assemblies feeding motors, VFDs, PLCs, and general power circuits. Type 3 SPDs are installed close to sensitive loads such as automation panels, servers, or instruments. In a custom engineered panel, a cascaded coordination approach is usually preferred: Type 1 at the incomer, Type 2 downstream, and Type 3 at the point of use. Correct energy coordination and lead-length control are critical to achieve the intended protective level and avoid overstressing downstream electronics.

SPD coordination in IEC 61439 panels is based on the SPD manufacturer’s backup protection data and the panel’s verified short-circuit design. The upstream device may be an ACB, MCCB, or gG/aM fuse, but it must be selected to clear fault conditions without disconnecting healthy circuits unnecessarily. The SPD typically requires a dedicated backup fuse or MCCB with the specified maximum rating to ensure safe disconnection at end-of-life or during severe surge stress. Selectivity, short-circuit withstand, and cable cross-section must be checked together. In custom panels, panel builders also verify that the SPD connection method does not reduce the assembly’s declared Icw or Icc values and that the protective device coordination supports the required service continuity.

The panel assembly is governed primarily by IEC 61439-1 and IEC 61439-2, which cover low-voltage switchgear and controlgear assemblies and verified performance. The SPD itself is normally evaluated to IEC 61643-11 for low-voltage surge protective devices connected to AC power systems. If the installation is in a hazardous area, IEC 60079 series requirements may also apply. For arc fault containment and internal fault behavior, IEC/TR 61641 may be relevant to the enclosure design. In practice, the panel builder must ensure the SPD’s voltage rating, backup protection, thermal performance, and installation method are compatible with the assembly’s verified design approach under IEC 61439.

Sizing starts with the system voltage, earthing arrangement, and exposure level. For 400/230 V systems, the SPD’s Uc must match the network configuration, such as TN-S or TT, and the voltage protection level Up must remain low enough to protect downstream equipment. For 690 V industrial panels, the SPD must be specifically rated for the higher operating voltage and installed with suitable backup protection. Key parameters include nominal discharge current In, maximum discharge current Imax, impulse current Iimp for Type 1 devices, and the ability to withstand temporary overvoltages. In a Custom Engineered Panel, the selection must also account for the panel’s fault level, conductor length, ambient temperature, and the presence of sensitive electronics such as VFDs, PLCs, and protection relays.

Yes. Many modern SPDs for Custom Engineered Panels include dry contact signaling, plug-in cartridge status indication, and communication-capable modules that can be integrated into SCADA or BMS architectures. This is valuable for critical facilities because it allows maintenance teams to detect loss of protection before the next surge event occurs. In engineered panels, the remote alarm output is typically wired to a PLC digital input, BMS controller, or annunciator. For higher asset reliability, the panel specification may include pre-failure warning, phase status, and replaceable module indicators. This improves maintainability and supports preventive maintenance strategies in compliance with the operational intent of IEC 61439 assemblies.

The most important rule is to keep the SPD connection leads as short and direct as possible. Excessive conductor length adds inductance, which increases residual voltage and reduces protection effectiveness. In IEC 61439 Custom Engineered Panels, the SPD should be mounted close to the incomer or protected busbar, with clean routing to phase and protective earth terminals. The connection to PE should be especially short and low impedance. Cross-sectional area, torque, segregation from power wiring, and enclosure layout also matter. Where practical, use coordinated busbar tapping or dedicated surge terminals. This design discipline is essential for protecting VFDs, PLCs, soft starters, and communication equipment from fast transient impulses.

SPDs contribute to heat rise because MOV-based devices have leakage current and may dissipate energy during transient suppression. In IEC 61439-2 panels, this must be considered in the verified thermal design of the assembly. The panel builder may need to provide spacing, ventilation, heat-resistant compartment placement, or derating for high ambient conditions. This is especially important in compact custom engineered panels with MCCBs, contactors, VFDs, and control power supplies already contributing to internal heat. If the SPD is installed near sensitive electronics, thermal and electromagnetic separation should both be checked. The final arrangement must preserve the panel’s declared temperature-rise limits while maintaining the SPD’s protective performance.

A common configuration is a Type 1+2 SPD at the main incomer, followed by Type 2 SPDs in feeder sections and Type 3 devices near sensitive loads. In industrial switchboards, this may be combined with ACB incomers, MCCB feeders, motor starters, VFDs, soft starters, and protection relays. The SPD modules usually include pluggable cartridges, visual status indicators, and remote alarm contacts. The design is coordinated with the busbar rating, panel fault level, and backup protection devices to keep the assembly compliant with IEC 61439-1/2 and the SPD itself aligned with IEC 61643-11. This layered approach is widely used in manufacturing plants, water facilities, commercial buildings, and critical infrastructure to maximize uptime and equipment protection.