Surge Protection Devices (SPDs) are now a requirement under the 18th Edition, but not every install needs the same level of protection. Selecting the wrong device can leave circuits exposed — or add unnecessary cost. This guide explains SPD types, when each is used, and how to match protection to your installation.

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What Does a Surge Protection Device Do?

An SPD diverts dangerous voltage spikes — caused by lightning, switching operations, or grid disturbances — safely to earth before they damage equipment. Without one, surges can knock out EV chargers, heat pumps, servers, alarms, or emergency lighting.

SPD Types Explained (Type 1, 2, 3)

• Type 1 SPD — Installed at the origin. Handles high-energy lightning currents; required where a building has an external LPS/lightning protection.
• Type 2 SPD — Installed at distribution boards. Protects against switching surges and residual lightning energy. The standard choice for most domestic and commercial installs.
• Type 3 SPD — Point-of-use protection. Safeguards sensitive kit (PCs, TVs, servers) and is always used in addition to upstream Type 2.

👉 Combined Type 1+2 SPDs are common in consumer units, giving broad coverage in one module.

How to Choose the Right SPD

• Supply type: TN-C-S (PME), TN-S, or TT will influence discharge ratings and device selection.
• Location/risk: Domestic vs commercial/industrial; lightning exposure; criticality of loads.
• Load sensitivity: EV chargers, heat pumps, IT, life-safety systems often require stronger protection.
• Regulatory baseline: BS 7671:2018+A2:2022 — SPDs must be installed unless a documented risk assessment justifies omission.

Example setups:

• Small domestic job with an EV charger → Type 2 SPD kit in the EV/consumer unit.
• Commercial site with an LPS → Type 1+2 at origin + Type 2 at local DBs.
• Server room or lab → Type 2 at DB + Type 3 local plug-in for the rack/endpoint.

Installation & Coordination Rules

• Install as close as possible to the incomer or protected load (observe the 10 m rule).
• Coordinate in series: Type 1 (origin) → Type 2 (DBs) → Type 3 (equipment).
• Protect the SPD with a correctly sized MCB as per the manufacturer’s datasheet.
• Keep conductors short and direct (L, N, and PE) with solid earthing for effective discharge.

Common Mistakes to Avoid

• Fitting only a Type 3 without upstream Type 2.
• Exceeding ~10 m between SPD and the sensitive load without adding a downstream SPD.
• Mixing brands without checking coordination guidance.
• Ignoring the SPD status window — failed devices often sit unnoticed.

Compliance & Cost Considerations

• SPDs are mandatory in most cases under BS 7671 A2; absence typically flags on an EICR.
• Typical device cost: ~£40–£200 depending on type/rating — far less than replacing damaged equipment or lost uptime.
• Some insurers now require surge protection for policy compliance.

FAQs

Do houses need surge protection?

Yes. Modern homes (EV/heat pump/PV/smart tech) should have at least a Type 2 SPD.

Do SPDs need an MCB?

Yes — they require overcurrent protection sized to the manufacturer’s instructions.

Does an RCD protect against surges?

No. RCDs detect earth leakage; SPDs handle transient overvoltages.

What is the 10 m rule?

If sensitive equipment is more than ~10 m from an upstream SPD, add supplementary protection near the load.

How do I know if an SPD has failed?

Most include a visual indicator; replace immediately if it shows red/fault.

✅ Key Takeaway

Match the SPD to the site risk and equipment sensitivity. For most homes, a Type 2 SPD is sufficient; lightning-exposed or commercial sites often need Type 1+2 at the origin, with Type 3 for sensitive endpoints.

👉 Browse our full range of Surge Protection Devices, including Type 1, Type 2, Type 1+2, and point-of-use options for EV, heat pump, and three-phase installs.