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DC Surge Protection (1000V) for Solar PV Explained

Surge Protection

DC Surge Protection for Solar (1000V)

DC surge protection looks like AC surge protection but is a different product, and fitting the wrong one on a solar string is a genuine safety risk.

Quick answer

Use a DC-rated SPD (tested to BS EN 61643-31) with a voltage rating that suits your string, 600V or 1000V for the WCED range. Fit it at the string combiner or inverter DC input, with short leads to the earth bar.

Why DC SPDs are different

AC current naturally passes through zero many times a second, which helps extinguish the arc inside a surge device after it operates. DC does not, so a DC SPD needs a design that can interrupt a sustained DC follow-current. An AC SPD used on DC may not do this, and can overheat or fail dangerously.

Never use an AC SPD on a DC circuit

Check the voltage and current type on the rating plate before fitting. The standard for PV DC SPDs is BS EN 61643-31, not the AC standard BS EN 61643-11.

Choosing the voltage rating

The SPD’s maximum continuous DC voltage must exceed the open-circuit voltage of the string, including cold-weather uplift, otherwise the device can conduct continuously. Choose the 600V or 1000V version to suit the system, and check the inverter’s maximum input voltage.

Where to fit it

  • At the string combiner box, which gives you isolation and protection in one enclosure
  • At the inverter DC input if no combiner box is used
  • Close to the earth bar, with short, direct leads as for any SPD

The WCED solar PV combiner box is a dual-string 1000V DC unit with a DC isolator (BS EN IEC 60947-3) and DC SPD (BS EN 61643-31). Standalone 2 and 4 pole DC SPD modules are available for existing enclosures. For the AC side, see surge protection for solar and heat pumps.

Shop DC surge protection

1000V DC combiner boxes and standalone DC SPD modules.

Combiner boxesDC SPD modules

Frequently asked questions

What is the difference between a combiner box and a standalone DC SPD?

A combiner box includes the DC isolator and SPD in one enclosure and suits new installs. Standalone modules suit adding protection into an existing enclosure.

Do I still need AC surge protection if I fit DC protection?

Yes. They protect different sides of the inverter and neither replaces the other.

How often should a DC SPD be checked?

Check the status indicator at routine inspections and after any known surge event. A red or absent indicator means the device has done its job and needs replacing.

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