BS 7671 Amendment 4: What Solar Installers Need to Know About DC Surge Protection

Amendment 4 to BS 7671 brings important changes for the electrical industry, including updates relevant to solar PV, battery storage and bidirectional power systems. But what does it actually mean for installers working with DC isolation and surge protection?

Published on 15 April 2026, BS 7671:2018+A4:2026 is the latest amendment to the 18th Edition IET Wiring Regulations.

There is currently a six-month transition period, meaning installations can be designed to either the previous or amended version of BS 7671 until 15 October 2026. After this date, the previous version is due to be withdrawn.

For solar installers, this makes now a good time to understand what the changes mean in practice — particularly when specifying protection on the DC side of PV installations.

What is changing on 15 October 2026?

The important thing to understand is that Amendment 4 itself isn’t suddenly being introduced on 15 October.

It was published in April and can already be used.

15 October marks the end of the transition period.

From this point, the previous version — BS 7671:2018+A2:2022+A3:2024 — is due to be withdrawn, making BS 7671:2018+A4:2026 the relevant current edition.

Amendment 4 reflects how electrical installations are changing, with greater consideration given to technologies including battery storage, renewable generation, power conversion equipment and bidirectional power flow.

For those working in solar, it makes correct equipment selection and system design increasingly important.

So, does Amendment 4 mean every solar PV system needs a DC SPD?

This is where some of the conversation around Amendment 4 can become misleading.

Amendment 4 should not be interpreted as simply saying that every solar PV installation now requires the same DC surge protection arrangement.

Surge protection needs to be considered as part of the individual installation.

The characteristics of the PV system, equipment being protected, installation design, existing protection and applicable requirements all need to be considered when determining the appropriate solution.

That’s an important distinction.

The objective isn’t to simply add the highest level of protection possible.

It’s about specifying the right protection for the installation.

Why does DC surge protection matter in solar PV?

Solar PV installations contain sensitive electrical and electronic equipment that can be affected by transient overvoltages.

These are short-duration increases in voltage that can potentially damage equipment within an electrical installation.

A Surge Protection Device — or SPD — is designed to limit transient overvoltages and divert surge current away from equipment.

However, the presence of an SPD alone doesn’t mean the installation has been appropriately protected.

The SPD itself needs to be correctly selected for the system.

For solar installations, that means considering equipment specifically designed for the DC side of photovoltaic systems, alongside factors including voltage, system configuration and the type of protection required.

Type 2 or Type 1+2 DC SPD?

This is likely to become one of the most common questions installers encounter when specifying DC protection.

The important thing is not to think of the options as:

Type 1+2 = better
Type 2 = worse

They perform different functions.

Type 2 DC SPD

A Type 2 SPD can provide protection against transient overvoltages, including those caused by switching events and induced surges.

Depending on the installation and applicable requirements, Type 2 protection may therefore be appropriate.

Type 1+2 DC SPD

A combined Type 1+2 device provides both Type 1 and Type 2 characteristics.

Type 1 capability is relevant where protection against higher-energy lightning impulse currents is required as part of the installation’s overall lightning and surge protection strategy.

The correct choice therefore comes back to the installation itself.

Not more protection. The right protection.

A higher specification shouldn’t automatically be treated as the correct specification.

What about 600V vs 1000V DC protection?

SPD type isn’t the only decision installers need to make.

Voltage selection matters too.

The DC voltage within a solar array depends on factors including the modules being used, number of modules within a string, temperature conditions and overall system configuration.

Protection equipment therefore needs to be suitable for the maximum voltage that can occur within the system.

For example, protection equipment rated to 600V shouldn’t be used where the system requires equipment capable of operating at a higher DC voltage.

Equally, specifying a 1000V product doesn’t inherently make an installation safer or better than a correctly selected 600V product.

It comes back to appropriate system design.

Understanding the numbers on a DC SPD

Looking at an SPD datasheet can present installers with several different ratings.

Four worth understanding are:

Uc — Maximum Continuous Operating Voltage

The maximum voltage that can continuously be applied to the SPD under its specified operating conditions.

Up — Voltage Protection Level

The level to which the SPD limits transient overvoltage under its specified test conditions.

In — Nominal Discharge Current

A specified surge-current value the SPD is designed to withstand repeatedly under defined test conditions.

Imax — Maximum Discharge Current

The maximum discharge current the SPD can withstand under its relevant test conditions.

You may also see Iimp — Impulse Current, particularly when looking at Type 1 protection.

These figures shouldn’t be considered independently. Together they help establish whether a particular SPD is appropriate for the electrical characteristics of the installation.

Don’t forget the DC isolator

Surge protection is only one part of the DC protection arrangement.

Correct isolation is equally important.

Switching DC is different from switching AC. With AC, the current naturally passes through zero during each cycle. DC doesn’t behave in the same way, making appropriate equipment selection particularly important when switching DC loads.

For PV installations, installers therefore need to consider whether the switch-disconnector is specifically suitable for the application.

This can include consideration of:

• System voltage
• Current
• Number of poles
• PV configuration
• Switching arrangement
• DC-PV utilisation category
• Manufacturer requirements

Simply looking at the headline voltage and current printed on a device doesn’t necessarily tell the whole story.

Where do pre-wired DC isolators fit in?

A DC isolation and surge protection arrangement can involve multiple components and electrical connections.

Using a factory pre-wired assembly can reduce the amount of assembly and termination that needs to take place on site.

For installers, this can provide a more consistent and repeatable approach while reducing installation time.

It does not, however, remove the need to correctly specify the product.

Installers still need to establish the requirements of the individual PV system before selecting the appropriate assembly.

That includes answering questions such as:

How many strings does the system have?

What is the maximum DC voltage?

What type of SPD is appropriate?

Is the isolation equipment correctly rated for the PV application?

Once those questions are answered, selecting the appropriate DC protection becomes much clearer.

What should solar installers do before 15 October?

The transition to Amendment 4 provides an opportunity for installers to review the way DC protection is being specified rather than waiting until the previous edition is withdrawn.

A sensible starting point is to:

• Review current DC isolation and SPD products being installed.
• Understand the difference between Type 2 and Type 1+2 protection.
• Check how maximum PV system voltage is being calculated and specified.
• Check that DC isolation equipment is suitable for its intended PV application.
• Review current product datasheets and technical evidence.
• Familiarise yourself with the relevant changes within BS 7671:2018+A4:2026.

The key is not to respond to Amendment 4 by simply adding more equipment.

It’s to understand the installation and specify the appropriate protection accordingly.

Eco-ESS DC Isolation & Surge Protection

At Eco-ESS, our approach is to make the specification and installation of renewable-energy electrical infrastructure simpler while maintaining a strong focus on correct product selection.

Our pre-wired solar PV DC isolator and surge protection solutions combine DC isolation and surge protection within factory-assembled units, with configurations available for different PV system requirements.

For installers, this reduces the amount of assembly and termination required on site while providing a consistent protection arrangement.

The correct configuration still depends on the individual installation — including string configuration, system voltage and required SPD type.

Need help selecting the right DC protection for an installation?

Explore Eco-ESS DC Isolation & Surge Protection and contact the team today.