Surge Protection: Why It Fails — and How to Design Against It

Protection in Theory vs Protection in Practice

Surge protection is widely accepted as a critical component in luminaire and control gear design — yet lighting systems continue to fail in the field due to transient overvoltage. These failures typically stem not from the absence of surge protection, but from incorrect SPD selection, poor coordination, or environmental degradation.

For engineers working on outdoor, mining, or industrial lighting projects, specifying surge protection means more than ticking a box. It requires an understanding of how surge currents behave, how protection devices respond and how to validate system integrity long after commissioning.

SPD Type Definitions

• Type 1 surge protection device (SPD) is a heavy-duty, first-line-of-defence device installed at the main electrical service entrance of a building. Its purpose is to discharge very high-energy surges, such as those caused by direct or nearby lightning strikes, safely to the ground before they can enter the building's electrical system.

  
  

• Type 2 surge protection device (SPD) is a widely used and highly effective protector for safeguarding a building's electrical installations and equipment from transient overvoltage’s. It is installed downstream of the main service entrance at a distribution board or sub-panel and is considered the second line of defence in a layered surge protection system.

  
  

• Type 3 surge protection device (SPD) provides the final layer of protection for sensitive electronic equipment at the point of use. These devices have the lowest discharge capacity of all SPD types and are only effective when used in coordination with upstream Type 1 and Type 2 SPDs.

  
  

Understanding Surge Events in Lighting Applications

Surges can be classified by amplitude, duration and source:

• Switching Surges: Often caused by load shedding, capacitor bank switching, or generator startup. Typically lower in amplitude (1–3kV) and duration, but frequent.

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• Indirect Lightning Surges: High-energy events induced through electromagnetic coupling or line entry. These can reach 10kV or more.

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• Direct Strikes or Earth Potential Rise (EPR):Rare but devastating, often exceeding 20kV with extremely high di/dt.

  
  

For lighting systems, especially those mounted on metal poles with long cable runs, even indirect surges can cause catastrophic failure if not properly managed.

Why Surge Protection Fails in the Field

• Inadequate Clamping and Let-Through Voltage

  Many SPDs clamp at 600V or higher, far beyond the breakdown voltage of typical LED drivers (350–450V). If the let-through voltage exceeds the driver’s max withstand rating, failure is inevitable.

  
  

• Underrated SPD Current Rating

  Surge protection devices are often specified by voltage, but the peak current capacity (Imax) is just as important. A 10kA-rated SPD will likely survive a single large event — but cumulative surges without proper coordination can wear it down undetected.

  
  

• No Coordination Between SPD and Driver

  Driver protection circuits and luminaire SPDs must be coordinated to avoid double-clamping or destructive oscillation. IEC 61643 recommends upstream-downstream coordination verified via testing, not assumption.

  
  

• Lack of Earth Reference

  SPDs require a low-impedance earth to safely dissipate surge energy. Without a proper earth reference (greater than 10Ω), surge current seeks alternate paths — often through the driver, optics, or PCB.

  
  

• SPD Ageing and End-of-Life

  Metal oxide varistors (MOVs) degrade with each event. After repeated exposure, clamping time increases and performance degrades silently. Without diagnostic indicators or replacement intervals, failure is only noticed post-event.

  
  

How to Prevent Surge Failures in Lighting Systems

• Specify SPDs Rated for Local Conditions

  In South Africa, 10kV/10kA is the minimum recommendation for outdoor installations. For high-risk zones (mines, substations, rural poles), 20kV/20kA should be considered.

  
  

• Verify Let-Through Voltage Compatibility

  Ensure SPD clamping voltage does not exceed the LED driver’s maximum input surge withstand (typically greater than 450V). Use coordinated device specs.

  
  

• Ensure Proper Earthing

  SPDs are only effective if the earth path is robust. SANS 10142-1 requires a verified earth electrode resistance; we recommend regular inspection and resistance logging per site.

  
  

• Use Replaceable SPD Modules

  Magnitech luminaires are available with external SPD options for diagnostic access and field replacement, ensuring long-term protection without replacing the full fitting.

  
  

• Protect at Multiple Levels

  Where feasible, use Type 2 SPDs at distribution boards and Type 3 SPDs at luminaire level — ensuring multi-stage energy dissipation and better clamping response.

  
  

Example Specification Wording“Each luminaire shall include integral 10kV/10kA surge protection, with optional upgrade to 20kV. The SPD must be replaceable and tested in accordance with IEC 61643-11 and SANS 10142-1.”

Magnitech’s Surge Strategy

Every Magnitech product is engineered for the realities of Southern African sites — including:

• 10kV SPDs as standard, with 20kV options

• Driver-SPD coordination testing

• Ingress-protected IP66 housings

• Replaceable SPD options for long-term serviceability

Conclusion

Surge protection is not a “nice to have” — it’s essential infrastructure. And just like any component, it must be specified, installed, tested, and maintained to do its job.

When systems go down during load shedding or lightning season, it's not always the surge — it's the spec. Let’s fix that.

Need support specifying surge protection correctly?

Contact our technical team for site-specific guidance, SPD matching, or to upgrade your lighting infrastructure.