Surge Protection Calculator — Formula
## 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
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
Exemplo Resolvido
230 V system, 10 kA surge (8/20 us), MOV clamping ratio 2.5x.
- System peak: 230 x sqrt(2) = 325 V
- Clamping voltage: 325 x 2.5 = 813 V
- Energy: 813 x 10,000 x 20e-6 = 162.6 J
- Peak power: 813 x 10 = 8,130 kW