Surge Protection Devices in a Consumer Unit: Do You Need One?
Updated: Oct 9
If you are having a new consumer unit fitted in a typical home, BS 7671 now expects it to include a surge protection device (SPD) unless you, as the owner, decide you do not want one and accept the risk of damage to your equipment. An SPD is a module in the consumer unit that diverts short, high-voltage spikes to earth before they reach your wiring and everything plugged into it. It adds modestly to the cost of a board change and cannot protect against everything, so it helps to know what it does before you decide.
What is an SPD, and what does it protect against?
An SPD protects against transient overvoltages, which the IET defines as short, high-magnitude voltage peaks with fast-rising edges, lasting no more than a millisecond and ranging from a few volts to many thousands of volts. When one arrives, the SPD conducts it to earth and limits the voltage the rest of the installation sees.
These surges come from two places:
Lightning: usually not a strike on your house, but a strike on or near an overhead power or telephone line that sends a surge along the line into nearby properties.
Switching inside buildings: equipment that switches heavy loads can create spikes. The IET says EV charging, heat pumps and speed-controlled washing machines have made transients much more likely inside homes.
The damage is not always dramatic. The IET points out that a surge can cause instant failure, or damage that only becomes evident over a longer period, which is why a router or TV that dies early is rarely blamed on a surge.
Is an SPD a requirement in a consumer unit?
For new work, broadly yes, with an opt-out. Regulation 443.4.1 of BS 7671, in the form introduced by Amendment 2 in 2022, says protection against transient overvoltages shall be provided where the consequences of an overvoltage could result in serious injury to, or loss of, human life, failure of a safety service, or significant financial or data loss.
For all other cases, which covers most homes, it says protection shall be provided "unless the owner of the installation declares it is not required due to any loss or damage being tolerable and they accept the risk of damage to equipment and any consequential loss". In other words, the default is to fit one, and leaving it out is your decision to make once you have been told the risk. The IET's summary is that the decision sits with the owner, who should be given enough information to make it.
Two things this does not mean:
It is not retrospective. An existing installation without an SPD is not unsafe just because the rules changed. Electrical Safety First's guidance is that there is no legal requirement to upgrade an existing installation to current standards.
It does not fail an EICR in a normal home. Electrical Safety First's coding guide gives a missing SPD a C3 (improvement recommended) only where the regulation makes one mandatory, such as where lives are at risk. It is never listed as a C1 or C2.
The current edition of the regulations is BS 7671:2018+A4:2026, with Amendment 3 remaining valid until 15 October 2026. The IET's published list of the main changes in Amendment 4 does not mention surge protection, so ask your electrician which version your work is designed to.
SPD consumer unit options and what they cost
In a home, the SPD is usually fitted inside the consumer unit, and combined Type 1 and Type 2 devices are made for exactly that position. When we fit a new board as part of a consumer unit replacement, the SPD is designed in from the start, which is the cheapest and neatest time to add one.
The IET describes three types:
Type 1: installed at the origin of the installation, where the supply comes in.
Type 2: installed at sub-distribution boards. Combined Type 1 and 2 devices are available for consumer units.
Type 3: installed close to a particular piece of equipment, and only ever as a supplement to a Type 2, never on its own.
On cost, the IET's consumer guidance says an SPD may cost as little as a few hundred pounds, which it asks you to weigh against the cost of the installation and the equipment connected to it, including computers, TVs, smoke detection and boiler controls.
You do not always need a new board to get one. The IET says an SPD can be fitted to an existing consumer unit where there is physical space, or in a separate enclosure next to it where there is not. Whether that is sensible depends on the age and condition of the board. If it is an old unit with signs of wear, our guide to old fuse box signs it needs replacing will help you judge whether to spend the money on the existing board or put it towards a new one.
What an SPD cannot protect against
An SPD is one layer, not a shield around the house.
Surges that come in another way. A surge can arrive through a telephone line, a cable TV feed or an aerial. The IET warns that protecting the power installation alone can leave another route in. Those services need their own protection.
Shock and overload. An SPD does nothing for electric shock (that is the RCD's job) or for an overloaded cable (that is the circuit breaker's).
Direct lightning damage to the building. SPDs deal with the surge on the wiring. Structural lightning protection is a separate system.
It is also worth checking your home insurance. The IET notes that some policies may say equipment must be covered by an SPD or they will not pay out on a claim.
Where an SPD earns its place
For most homes the case is simple: a modest cost set against the value of the wiring, the boiler controls, the smoke alarms and the electronics in the house. The case is stronger if:
the supply or the phone line reaches the house overhead
the house has an EV charger, a heat pump or other equipment that switches large loads
people work from home and losing a computer or data would cost money
there is a monitored alarm, medical equipment or anything that must keep working
We fit SPDs as part of consumer unit work across Shifnal, Telford, Wolverhampton and the surrounding area, including anyone looking for an electrician in Bridgnorth. If you would like to know whether your board has room for one, or whether a new board makes more sense, SM Electrical can take a look.
SPD questions, answered
How do I know if my consumer unit has an SPD?
Look inside the front cover for a module labelled SPD or surge protection, usually near the main switch. If you cannot tell, an electrician can confirm it, and an EICR will record it.
Is a plug-in surge protected extension lead the same thing?
No. A surge-protected extension lead protects only what plugs into it, and it is no substitute for protection at the consumer unit. The IET's rule for Type 3 devices shows the thinking: protection close to equipment is only ever a supplement to protection at the board, not a replacement for it.
Can I decline an SPD?
Yes, for an ordinary home where none of the mandatory cases applies. The electrician should explain the risk and record your decision. What you are declining is protection for your equipment, and the regulations leave that choice to you.
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