Surge Protection (SPD): Do London Properties Actually Need It?

A Surge Protection Device clamps voltage spikes before they reach your appliances. When the line voltage spikes above its rated threshold (typically 1.5kV for a Type 2 SPD), an internal MOV (metal-oxide varistor) shunts the excess current to earth, holding the downstream voltage at a survivable level.

SPDs sit on the incoming line in your consumer unit. They are sacrificial — a major surge degrades the MOV and the device must be replaced. Most have a status flag that turns red when end-of-life.

Type 1 SPDs handle direct lightning strikes — measured in 10/350μs waveform. Required on installations with an external lightning protection system (LPS) per BS EN 62305. Rare in London domestic.

Type 2 SPDs handle indirect lightning and switching transients — 8/20μs waveform. This is the standard domestic device, fitted in the consumer unit. About £80 installed delta on a board upgrade.

Type 3 SPDs are point-of-use devices for sensitive equipment — fitted close to the load, typically inside an A/V cabinet or server rack. Used in addition to Type 2, not instead of.

The argument against SPD in London goes: the supply is underground, lightning cannot reach it, the LV network is heavily damped, so SPDs are unnecessary. This was largely true in 1995. It is much less true in 2026.

Real surge sources on a modern London installation include UKPN feeder switching (multi-kV transients seen at the consumer unit during ring main reconfiguration), large inductive loads on the same LV substation (lift motors, HVAC compressors), neighbour solar inverter switching, and EV charger contactor operations on shared transformers.

These are smaller surges than lightning but they happen weekly. Cumulative degradation of sensitive electronics (smart TVs, gaming PCs, home automation hubs, EV charger control boards) is the modern threat model.

Regulation 443.4.1 requires SPDs where the consequence of a surge would cause: serious injury or loss of human life, interruption of public services and damage to cultural heritage, interruption of commercial or industrial activity, or affect a large number of co-located individuals.

For routine domestic installations BS 7671 uses a risk calculation (CRL formula based on lightning ground flash density and other factors). In London, the CRL almost always allows omission — meaning SPD is a C3 (improvement recommended) rather than required.

Exception: any installation with PV, EV charging, home battery storage, or significant home-automation equipment now sits in territory where the cost-of-loss makes SPD a default recommendation. Most NICEIC contractors install SPD by default on board upgrades in 2026.

Type 2 SPD installed in a new consumer unit: roughly £80 on top of the standard board change. Retrofit into an existing board: £120–£150 if there is space and the supply characteristics are suitable.

For our standard £750 fuse-board upgrade package we include a Hager Type 2 SPD as standard. With AFDD added (HMO-spec) the package is £999. A Type 1+2 combined device for properties with external LPS adds about £180.

Insurance angle: a handful of UK home insurers now offer a 5–10% premium reduction for installations with documented SPD protection plus surge-rated extension leads. Worth a five-minute phone call at next renewal.