Surge Protection Devices (SPD)

In a main distribution board, the usual choice is a Type 1 or Type 1+2 SPD when the site has an external lightning protection system, overhead incoming lines, or high lightning exposure. Type 1 devices are designed for partial lightning current discharge, while Type 1+2 combines that capability with residual surge limitation in one module. Selection should be based on IEC 61643-11, with the installation approach aligned to IEC 60364-5-534 and the assembly rules of IEC 61439-1/2. The panel builder must confirm Uc, discharge current rating, voltage protection level, backup overcurrent protection, and coordination with the earthing system. In many MDBs, pluggable modules with remote indication are preferred for maintenance.

SPD coordination is staged so that the highest energy device is installed closest to the service entrance and finer protection is installed downstream near sensitive loads. A common architecture is Type 1 or Type 1+2 at the main incoming board, Type 2 in sub-distribution boards, and Type 3 near PLCs, drives, meters, or lighting controllers. Coordination must account for cable length, impedance, and the residual voltage passed from the upstream SPD. IEC 61643-11 and IEC 60364-5-534 provide the framework, but the manufacturer’s coordination tables are essential because devices from families such as DEHNguard, ABB OVR, Phoenix Contact VAL, or Schneider Acti9 are tested as systems. Good coordination reduces let-through voltage and prevents premature failure.

Yes, and it is often recommended because VFDs are highly sensitive to transient overvoltages on the supply side. In a variable-frequency-drive panel, a Type 2 SPD is commonly installed upstream of the drive feeder, with additional Type 3 protection used for control circuits, comms modules, and encoders where necessary. The selection must consider the VFD input voltage, system earthing, upstream breaker, and the need to avoid nuisance operation during switching events. For panels built to IEC 61439, the SPD must be coordinated with the enclosure thermal design and the feeder short-circuit rating. Brands such as Siemens SENTRON, ABB OVR, and Phoenix Contact VAL series are widely used in industrial drive panels.

The key ratings are nominal voltage, maximum continuous operating voltage (Uc), nominal discharge current, impulse current rating for Type 1 devices, voltage protection level, short-circuit withstand/back-up fuse rating, and the number of poles. For AC systems, also verify the network configuration: TN-S, TN-C, TT, or IT. In IEC 61439 panel assemblies, the SPD must be compatible with the assembly’s rated current and prospective short-circuit current so that the protective device can clear faults safely. If the application is DC, such as a dc-distribution-panel, the polarity and DC Uc value are critical. Manufacturers like DEHN, ABB, Schneider Electric, and Phoenix Contact publish detailed selection tables for each product family.

SPDs should be installed as close as practical to the point of cable entry and the protective device feeding the circuit, with very short, straight conductor connections to reduce inductive let-through voltage. In a main board, that usually means placement near the incomer and the PE bar. In sub-panels and control panels, the SPD should be mounted near the feeder terminals or DIN rail assembly feeding the protected circuit. Long lead lengths degrade performance, so keeping the connection path minimal is more important than simply choosing a higher current rating. The panel designer should also check heat dissipation, segregation, accessibility for cartridge replacement, and whether the form of internal separation allows safe maintenance.

Yes, metering panels often need SPDs because electronic meters, revenue metering modules, communication gateways, and current/voltage transducers can be damaged by transient surges even when the power system appears stable. A compact Type 2 or Type 2+3 SPD is commonly used in metering panels, especially where long external cables, rooftop PV interfaces, or building automation communication links are present. In IEC 61439-compliant assemblies, the SPD should be chosen for the system voltage and coordinated with the meter protection scheme. Remote indication is useful because failed SPDs may not be visible during routine site checks, and end-of-life thermal disconnect improves reliability.

Pluggable SPDs have replaceable cartridges that allow maintenance without rewiring the whole device base, while fixed SPDs require replacement of the complete unit. In industrial panel assemblies, pluggable designs are preferred for critical boards because they reduce downtime and simplify service. Many product families from Phoenix Contact, DEHN, ABB, Siemens, and Schneider Electric offer pluggable versions with visual status windows and optional remote signaling contacts. Fixed devices can still be suitable in cost-sensitive or compact panels, but the maintenance strategy should be considered during panel engineering. For IEC 61439 assemblies, the chosen design must also fit the thermal layout and maintain safe accessibility.

They are strongly recommended in both applications, and in many projects they are effectively mandatory for continuity and equipment protection. Lighting distribution boards often feed electronic drivers, occupancy controls, and emergency lighting systems that are vulnerable to transient overvoltages. Busbar trunking systems can distribute surges across large building areas, so a Type 2 SPD at the relevant tap-off or feeder panel helps limit propagation. The exact requirement depends on the risk assessment, building code, and the lightning exposure of the site, but IEC 61643-11 and IEC 60364-5-534 provide the technical basis. In coordinated systems, the SPD selection should also align with the upstream MDB protection and the downstream load sensitivity.