Sizing a Type 2 SPD for a combined solar and EV site
In 40 kA, Imax 65 kA, 255 Vac — what those numbers mean when the strings and the charger share an earth.
A surge protective device is rated by two currents and one voltage, and all three get misread.
The three numbers
- In (nominal discharge current) — the surge the device can take repeatedly without degrading. Ours is 40 kA on the single-phase AC unit.
- Imax (maximum discharge current) — the one-off it can survive. 65 kA on the same unit.
- Uc (maximum continuous operating voltage) — 255 Vac. This must sit above the highest steady-state voltage the line reaches, including regulation swing, or the device conducts in normal service.
Why a combined site is different
Solar strings and an EV charger on the same earth create a loop. A strike on the array side does not stay on the array side. You need protection on the DC string, on the AC supply and, if the charger has its own DC bus, on that too.
Our SurgeTrap range covers all three: SARALA-2PACSPD-230V for single-phase distribution boards, SARALA-4PACSPD-415V four-pole for three-phase panels, and a DIN-rail DC+/DC− unit for PV strings, DC EV and battery banks.
Coordination, briefly
Type 1 at the service entrance where there is a direct-strike risk, Type 2 at the distribution board, and short leads — under 50 cm total including earth — between the device and the conductors it protects. A perfectly rated SPD on a long lead protects very little.
After a strike
SPD cartridges are consumable. Inspect the status window after any significant event, and treat replacement as maintenance rather than a fault.
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