Surge Protection Calculator

Calculate the energy absorption requirements and clamping voltage for surge protection devices (SPDs).

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V
kA
µs

8/20 microsecond is standard test waveform

Clamping V / System V peak; typical MOV = 2-3x

Clamping Voltage

813 V

Energy per Surge162.6 J
System Peak Voltage325 V
Peak Surge Power8,132 kW

Clamping Voltage vs Surge Duration

View formula & how it works →

Surge Protection Device Sizing

SPDs must absorb surge energy while limiting voltage to a safe clamping level that protects downstream equipment.

Formulas

V_clamp = V_peak x Clamping Ratio

Energy = V_clamp x I_surge x Duration

The standard test waveform for SPDs is 8/20 microseconds (8 us rise, 20 us to half-value).

SPD Categories (IEC 61643)

  • Type 1: Lightning current (10/350 us), installed at service entrance
  • Type 2: Surge current (8/20 us), at distribution panel
  • Type 3: Combination wave, at point of use

    • Example Calculation

    230 V system, 10 kA surge (8/20 us), MOV clamping ratio 2.5x.

    1. 01System peak: 230 x sqrt(2) = 325 V
    2. 02Clamping voltage: 325 x 2.5 = 813 V
    3. 03Energy: 813 x 10,000 x 20e-6 = 162.6 J
    4. 04Peak power: 813 x 10 = 8,130 kW

    Frequently Asked Questions

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