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 the SPD types available, 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 strikes, switching operations, or grid disturbances - safely to earth before they damage equipment. Without one, surges can knock out EV chargers, heat pumps, servers, or even safety-critical systems like alarms and emergency lighting.

SPD Types Explained (Type 1, 2, 3)

Not all SPDs do the same job. Here’s how the different types stack up - and when each one applies.

• Type 1 SPD – Installed at the origin. Handles high-energy surges from lightning, often required with lightning protection systems.
• Type 2 SPD – Installed at distribution boards. Protects against switching surges and residual lightning energy. Standard for most domestic and commercial installs.
• Type 3 SPD – Point-of-use protection. Safeguards sensitive equipment like PCs, TVs, and servers. Always used alongside upstream Type 2.

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

How to Choose the Right SPD

Your choice depends on several factors:

• Supply type: TN-C-S, TN-S, or TT earthing arrangements affect discharge ratings.
• Location: Domestic, commercial, or industrial sites with varying lightning risk.
• Load sensitivity: EV chargers, heat pumps, IT hardware, or alarms may demand stronger protection.
• Regulatory requirement: BS 7671:2018 A2 states SPDs must be installed unless a risk assessment justifies omission.

Example setups:

• Small domestic job with an EV charger → Type 2 SPD kit.
• Commercial site with lightning protection → Type 1+2 SPD at origin plus Type 2 downstream.
• Server room or lab → Type 2 at distribution board plus local Type 3 plug-in SPD.

Installation & Coordination Rules

Correct placement makes or breaks SPD performance. These are the golden rules for positioning and wiring.

• Install as close as possible to the incomer or protected load (observe the 10m rule).
• Always coordinate SPDs in series (Type 1 → Type 2 → Type 3).
• Protect the SPD circuit with a correctly sized MCB.
• Ensure short cable runs and solid earthing for effective discharge.

Common Mistakes to Avoid

SPDs are simple to fit, but errors in selection or installation can leave protection useless. Watch out for these pitfalls.

• Fitting only a Type 3 without upstream protection.
• Exceeding the 10m distance without adding additional SPDs.
• Mixing brands without checking manufacturer coordination rules.
• Overlooking the SPD status window - failed devices often go unnoticed.

Compliance & Cost Considerations

Fitting SPDs is about more than safety - it’s about staying within the regs and avoiding expensive downtime.

• SPDs are mandatory in most cases - missing protection can fail an EICR.
• Cost is typically £40–£200 depending on type and rating, far less than replacing damaged kit.
• Some insurers require surge protection for cover to remain valid.

FAQs

Installers and clients ask the same questions every time. Here are the straight answers you can rely on.

Do houses need surge protection?

Yes. Homes with EV chargers, heat pumps, or modern electronics should have at least a Type 2 SPD.

Do SPDs need an MCB?

Yes. They must be protected against overcurrent, following the manufacturer’s guidance.

Does an RCD protect against surges?

No. RCDs protect against earth leakage but don’t handle transient overvoltages. SPDs are required for that role.

What is the 10m rule?

SPDs should be installed within 10m of the equipment they protect. Beyond that, additional devices are needed.

How do I know if an SPD has failed?

Most have a visual indicator. Replace immediately if it shows red.

Key Takeaway

The right SPD depends on risk and installation type. For most homes, a Type 2 SPD is sufficient. For lightning-exposed or commercial sites, a Type 1+2 is essential. Add Type 3 for sensitive kit. Matching protection to need keeps systems compliant and reduces costly call-backs.

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