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 by BS 7671 unless risk is negligible
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+A4:2026
When SPDs are required.
BS 7671 Regulation 443.4 requires protection against transient overvoltages to be provided where the risk is not negligible. A formal risk assessment considers lightning density, supply type, cable runs and the consequences of equipment damage.
Domestic installations
A risk assessment is required for every new or modified installation. In most homes, the risk is not negligible, so Type 2 SPDs at the consumer unit are the standard solution.
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.
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:
- A risk assessment must be carried out for every installation.
- SPDs are required unless the assessed risk of transient overvoltage is negligible.
- 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?
Yes. BS 7671:2018+A4:2026 requires a risk assessment to be carried out. Unless the risk is assessed as negligible, surge protective devices (SPDs) must be installed to protect against transient overvoltages. This applies to most domestic, commercial and industrial installations.
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?
In almost every case, yes. The BS 7671 risk assessment considers lightning density, cable length, building size and the value of equipment. Modern homes are full of electronics — TVs, boilers, EV chargers, networks, smart devices — so the cost of SPDs is small compared with replacing damaged equipment.
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.