Surge Protection Explained
Stop voltage spikes
before they strike.
Surge Protection Devices (SPDs) shield your wiring, consumer unit and expensive electronics from lightning and switching surges. Here is how BS 7671 decides when they are required, and what type you need.
Why surges matter
One strike can destroy thousands of pounds of equipment.
A transient overvoltage is a brief, massive spike in voltage. It can come from a direct lightning strike, a nearby strike on the supply, or even switching operations on the grid. Without SPDs, that energy travels through your circuits and can destroy consumer units, boilers, TVs, computers, network gear and EV chargers.
- Protects against lightning and switching transients
- Reduces damage to appliances and electronics
- Helps prevent fire caused by arc-over in equipment
- Required where BS 7671 specifies serious consequences; otherwise discuss and document the owner's decision
What gets damaged
- Consumer units, MCBs, RCBOs and RCDs
- Smart TVs, games consoles and audio systems
- Boiler PCBs and smart heating controls
- EV chargers and solar inverter electronics
- CCTV recorders, routers and network switches
BS 7671:2018+A3:2024/A4:2026
When SPDs are required.
BS 7671 Regulation 443.4.1 requires protection against transient overvoltages where the consequences include serious injury, loss of life, failure of a safety service, or significant financial or data loss. In other cases the installation owner may declare the risk of damage and consequential loss tolerable; record that decision with the installation documentation.
Domestic installations
Type 2 SPDs at the consumer unit are common. Whether one is required depends on the consequences specified in Regulation 443.4.1 and, where permitted, the owner's documented decision about tolerable loss.
Lightning exposure
Properties in areas with higher lightning flash density, or with overhead supply cables, are at greater risk and benefit strongly from combined Type 1 + Type 2 protection.
Commercial & industrial
Businesses with critical equipment, servers, fire alarms, CCTV and production machinery should install coordinated SPDs at the origin and at distribution boards.
Sensitive electronics
Home offices, medical equipment, audio-visual systems and EV chargers all need protection. Type 3 local SPDs can add a final layer of defence close to the equipment.
Device types
Type 1, Type 2 and Type 3 SPDs.
Type 1 — Lightning current
Designed to handle direct lightning current entering the building. Usually installed at the origin of the installation, close to the main supply. Essential where overhead supplies or lightning rods are present.
Type 2 — Switching transients
The most common domestic and commercial solution. Installed in the consumer unit to protect against indirect lightning and switching surges from the grid. Often combined with Type 1 in a single unit.
Type 3 — Fine protection
Local protection fitted close to sensitive equipment — for example, behind a socket supplying a home office, server or AV rack. Must be used in coordination with upstream Type 2 protection.
Buildings with a lightning protection system (LPS)
Where a premises has a structural lightning protection system installed to BS EN 62305, any modification to the electrical wiring system — or the addition of new circuits — requires a risk assessment by a qualified lightning protection engineer before work commences. That assessment determines the surge protection required: the class and position of Type 1 SPDs, equipotential bonding arrangements, and co-ordination with the existing LPS. The findings must be incorporated into the design and recorded with the certification.
Industry guidance
BS 7671 and surge risk assessment.
Surge protection requirements are covered in BS 7671 Section 443 and Regulation 443.4. The IET and Electrical Safety First publish guidance on how to carry out the risk assessment and select the right SPD for the installation.
Key BS 7671 reference
Section 443 / Reg 443.4
A concise summary of what the standard covers:
- Assess whether the consequences in Regulation 443.4.1 require protection.
- In other cases, document any owner declaration that the risk is tolerable.
- Protection must be co-ordinated so upstream devices do not mask downstream ones.
- SPD installation, connection and earthing must minimise lead lengths for best performance.
- Type 1 SPDs are needed where there is a risk of direct lightning current.
FAQ
Common surge protection questions.
What is surge protection?
Surge protection limits sudden voltage spikes — caused by lightning strikes, switching transients or grid faults — so they do not damage wiring, consumer units, electronic appliances and sensitive equipment. It is fitted at the origin of the installation and sometimes at local points.
Is surge protection required by BS 7671?
Under BS 7671:2018+A3:2024/A4:2026 Regulation 443.4.1, SPDs are required where transient overvoltage could cause serious injury or loss of human life, failure of a safety service, or significant financial or data loss. In other cases the installation owner may declare the risk of damage and consequential loss tolerable. The decision should be documented; an owner declaration does not override the cases where protection is required.
What are Type 1, Type 2 and Type 3 SPDs?
Type 1 SPDs are installed where there is a risk of direct lightning current, typically at the main supply. Type 2 SPDs protect against indirect lightning and switching transients, usually in the consumer unit. Type 3 SPDs are local, fine-protection devices fitted close to sensitive equipment.
Do I need surge protection in a domestic house?
A Type 2 SPD is commonly fitted when a consumer unit is replaced or a new installation is designed. In an individual home, discuss the likely impact of a surge and the value of the equipment with your electrician. An owner may declare the risk of damage and consequential loss tolerable where Regulation 443.4.1 allows it; protection remains required in the serious-consequence cases covered by that regulation.
My building has a lightning protection system — what happens then?
Where a premises has a structural lightning protection system (LPS to BS EN 62305), any modification to the electrical wiring system or the addition of new circuits must be preceded by a risk assessment carried out by a qualified lightning protection engineer. That assessment determines the surge protection measures required — typically the class and location of Type 1 SPDs, bonding and co-ordination with the LPS — and the work should not commence until that advice has been received and incorporated into the design.
Can surge protection be added to an existing fuse board?
Often yes. A Type 2 SPD can usually be installed inside or next to an existing consumer unit, provided there is enough space and the earthing arrangement is suitable. Paul can assess this on site and advise the neatest, most compliant solution.
Protect your installation
SPDs fitted to BS 7671.
Paul carries out the risk assessment, specifies the right Type 1/2/3 SPDs and installs them neatly in your existing or new consumer unit.