In everyday language we talk about “power surges” when a device fails unexpectedly or an adaptor burns out. From an electrical point of view, however, it is important to distinguish between transient overvoltages (very short, high-energy peaks) and temporary or permanent overvoltages (sustained rises in voltage above the nominal 230/400 V). Both phenomena can damage equipment and compromise safety, but they behave very differently and require different protection strategies.
This guide explains in a practical way what overvoltages are, how they appear in low-voltage installations, what effects they have on equipment and which protection solutions are most commonly used in domestic, commercial and industrial environments. It also outlines the regulatory framework and shows how to apply it using devices and boards that are easy to integrate into a distribution system.
Along the way we will refer to solutions from Solera, such as modular surge protective devices (SPDs), combined circuit-breaker and surge protector units and multi-socket extensions with built-in surge protection, as well as pre-assembled protection boards and enclosures for demanding environments.
1) What exactly is an overvoltage?
In a low-voltage system, the supply is designed to operate around 230 V single-phase or 400 V three-phase, with a certain admissible tolerance. Whenever the voltage between conductors (or between a conductor and earth) rises clearly above this operating band, we speak of an overvoltage.
Not all overvoltages are the same:
- Transient overvoltages are extremely short (microseconds to milliseconds), but can reach several kilovolts. They are associated with lightning, switching operations and certain faults in the network or in loads.
- Temporary/permanent overvoltages last much longer (seconds, minutes or even continuously) and tend to be of lower amplitude, but still clearly above the nominal value (for example, 260–300 V in a 230 V system).
Both types can reduce the service life of devices, cause immediate failure or create conditions that increase fire risk. Protection therefore needs to be planned from the design stage of the installation and adapted to the environment and the sensitivity of the loads.
2) Transient overvoltages: very fast, very energetic
Transient overvoltages (often referred to as “surges”) are short-duration peaks with high energy content. They are typically caused by:
- Indirect lightning strikes on nearby lines or structures, which induce large voltage spikes on power and data conductors.
- Switching operations in the distribution network (switching transformers, capacitor banks, large motors, etc.).
- Switching of inductive or capacitive loads within the installation itself (motors, lifts, refrigeration, large LED drivers, power supplies for IT equipment).
Even when they do not cause an immediate, visible failure, these transients stress insulation, electronic components and contact surfaces. The result is often cumulative damage: equipment that “mysteriously” starts to fail more often, power supplies that become noisy or unstable, premature LED failure, intermittent resets of control electronics, and so on.
To deal with these surges, installations use surge protective devices (SPDs) of different types, coordinated from the origin of the installation to sensitive loads.
3) Temporary and permanent overvoltages: when 230 V stops being 230 V
Temporary or permanent overvoltages are sustained rises in voltage above the nominal supply. Common causes include:
- Neutral faults or poor connections in three-phase systems, which can cause one phase to rise well above 230 V in relation to neutral.
- Incorrect connection (for example, connecting single-phase equipment between two phases instead of phase and neutral).
- Network incidents or configuration errors in the distribution system that temporarily raise the supply voltage.
- Incorrect tap settings on transformers or local generation systems.
Unlike transients, which last microseconds or milliseconds, these overvoltages can persist for seconds, minutes or longer. Many devices designed for 230 V tolerate moderate deviations for a short time, but if, for example, the line remains at 260–280 V for several minutes, overheating, insulation stress and potential fire risk soon become critical.
To mitigate this risk, the installation can use permanent overvoltage protection devices (also called “POP” or “OVP” relays), which monitor the supply voltage and, when a threshold is exceeded, disconnect the circuit. Some combined devices integrate short-circuit/overload protection and overvoltage protection in a single modular unit, simplifying wiring and coordination.
4) Comparing transient and permanent overvoltages
| Aspect | Transient overvoltage | Temporary/permanent overvoltage |
|---|---|---|
| Duration | Microseconds–milliseconds | Seconds–continuous |
| Typical amplitude | Up to several kV | Typically 250–300 V in 230 V systems |
| Main causes | Lightning, switching, inductive loads | Neutral faults, mis-wiring, supply issues |
| Typical effects | Damage to electronics, insulation stress, data errors | Overheating, accelerated ageing, risk of fire |
| Protection strategy | SPDs type 1–2–3 coordinated in the installation | Overvoltage relays and combined protection devices |
5) Where overvoltages appear in real installations
Overvoltages are not limited to rural lines or heavy industry. Some typical scenarios include:
- Dwellings and small offices: sensitive electronics, routers, smart TVs, chargers, IT equipment and LED lighting all share the same circuits, often with limited surge protection beyond the main board.
- Shops and commercial premises: EPOS systems, refrigeration, air conditioning and lighting control rely on stable voltage and are susceptible to both transients and temporary overvoltages.
- Industrial workshops: frequent motor starts, contactor switching and the presence of inverters and drives generate internal surges that can propagate through the installation.
- Photovoltaic systems: lightning surges and switching on the DC side can couple into the AC side if SPDs are not correctly selected and installed.
- Electric vehicle charging points and swimming pools: outdoor environments with long cable runs and sensitive power electronics where surge and overvoltage protection is essential.
Because of this diversity, protection must be layered: from the origin of the installation to the final socket outlet or terminal, combining SPDs, overvoltage relays and good installation practices.
6) Regulatory and standards framework
In Europe, overvoltage protection is framed by the Low Voltage Directive 2014/35/EU and the general product safety legislation, which require that equipment and components are designed and tested to operate safely within their intended voltage range. Solera provides an overview of the main directives and regulations affecting low-voltage electrical equipment on its Directives and regulations page.
At installation level, the technical rules for design and verification in each country are based on the IEC 60364 series. In the United Kingdom, for example, the Wiring Regulations (BS 7671) set out requirements for protection against overvoltages of atmospheric origin and switching, and require an assessment of the need for surge protection in many domestic and commercial installations, particularly where sensitive equipment or safety-related systems are present.
These regulations converge on the same idea: overvoltages are a predictable risk that must be assessed, limited and documented through appropriate devices and wiring arrangements.
7) Surge protective devices (SPDs): types and application
SPDs are designed to divert surge energy away from protected equipment, limiting the voltage that appears at their terminals. In a typical low-voltage installation we distinguish three main types:
- Type 1: installed at the origin of the installation (often just after the main incoming device). They are designed to handle partial lightning currents and high-energy surges from the supply network.
- Type 2: installed in main and sub-distribution boards. They protect circuits and equipment against residual surges after type 1 devices and against switching surges generated within the installation.
- Type 3: located close to sensitive loads (sockets, terminal strips at equipment inlets, IT racks, etc.). They provide fine limitation of residual voltage for electronic devices.
Solera offers modular surge protective devices for DIN-rail mounting in low-voltage boards, with versions suitable for single-phase and three-phase installations. These are grouped in the modular surge protectors range, where you can find SPDs for AC and photovoltaic applications, with different discharge capacities and coordination options.
In addition to standalone SPDs, some Solera devices combine magnetothermal protection and surge protection in the same modular unit. This simplifies wiring, saves space in the board and makes it easier to comply with both overcurrent and overvoltage protection requirements in a coordinated way.
8) Permanent overvoltage protection
SPDs are not designed to open the circuit during a sustained rise in voltage. Their role is to limit fast surges, not to act as a disconnecting device for long-lasting events. For this reason, installations at risk of temporary or permanent overvoltage should incorporate overvoltage relays or combined devices that monitor the line voltage and trip when a threshold is exceeded for a given time.
These devices work as follows:
- They continuously measure the supply voltage.
- If the voltage exceeds a set limit (for example, 275–280 V in a 230 V system) for a defined period, they open the circuit to protect downstream equipment.
- Depending on the model, they may require manual reset or provide automatic reconnection once the voltage returns to acceptable values.
Installing such protection is particularly relevant in three-phase systems with single-phase loads, sites with frequent network disturbances, or where a neutral fault could cause dangerous overvoltages on one or more phases.
In practice, these relays are often installed on the DIN rail alongside SPDs and circuit-breakers, either as separate modules or as part of combined units that also offer short-circuit and overload protection.
9) Multi-socket extensions and local protection at socket level
Beyond the distribution board, sensitive equipment is often connected via multi-socket extensions, especially in offices, IT areas, workshops and home entertainment setups. If these power strips have no surge protection, all the work done at the origin of the installation may not be enough to protect laptops, routers, game consoles, servers or audio-visual systems.
For these situations, Solera offers multi-socket extensions with built-in surge protection within the ION range. Instead of a simple power strip, the user connects their devices through a unit that integrates a type 3 SPD, designed to clamp residual surges at the socket outlet and provide a first line of defence for connected electronics. You can explore these options in the section dedicated to special multipoint sockets with surge protection.
Used in combination with SPDs in the distribution board, these devices help to create a coherent protection chain from the origin of the supply to the most sensitive equipment.
10) Enclosures and pre-wired boards: protecting installations in demanding environments
In harsher environments (workshops, industrial areas, outdoor installations, temporary power for events, building sites, pool plant rooms, EV charging, etc.), the protection strategy must also consider mechanical resistance, IP rating and the way the board is installed and handled.
The Indubox family from Solera includes IP65 enclosures and pre-wired boards designed for industrial and site applications. Within this range there are distribution boxes, temporary work boards, connection panels and specific protection boards for photovoltaic systems, electric vehicle charging stations and swimming pools, among others. These solutions make it easier to integrate SPDs, overvoltage protection, differential devices and magnetothermal protection in a robust and well-organised enclosure.
If you need to design or specify this type of solution, you can use the Indubox enclosures and boards as a starting point and combine them with the modular surge protectors range to build a complete, coordinated protection system.
11) Wiring, coordination and good installation practice
Devices alone are not enough; how they are installed is equally important. Some key points:
- Keep connections short and direct: the cables connecting SPDs to the busbars or terminals should be as short and straight as possible. Excessive length increases the residual voltage seen by protected equipment.
- Ensure a good earthing system: SPDs rely on a low-impedance earth connection to discharge surge energy safely. A poor earth limits their effectiveness.
- Coordinate devices by type and location: type 1 at the origin, type 2 in distribution boards and type 3 close to sensitive loads. The characteristics of each should be compatible in terms of discharge capacity and residual voltage.
- Use suitable terminal blocks and wiring accessories: for distributing circuits and connecting SPDs close to loads, properly sized terminal blocks make it easier to maintain separation by function and to keep wiring clear. Solera offers dedicated terminal blocks for this purpose.
- Protect conductors mechanically in enclosures and at cable entries, especially in outdoor and industrial environments, to avoid damage that may lead to faults and overvoltages.
Good practice also involves labelling circuits, keeping diagrams and documentation up to date and ensuring that any modifications respect the original coordination of protection devices.
12) Maintenance and periodic checks
SPDs and overvoltage protection devices are not fit-and-forget components. Their internal elements are subject to ageing, especially after repeated surge events. Some recommendations:
- Visual checks: many SPDs include an indicator that changes colour when the device has reached end-of-life and must be replaced. These indicators should be checked during routine maintenance.
- Review of tripping events: if an overvoltage relay or combined protection device trips, it is important to investigate the cause (network disturbance, internal fault, mis-wiring) and not simply reset without analysis.
- Thermal inspection: in boards heavily loaded or in harsh environments, periodic thermal imaging can help detect hotspots related to poor connections or overstressed components.
- Documentation: keep a record of SPD installations, replacement dates and any major surge events (for example, after storms) to plan preventive maintenance.
13) Practical selection checklist
Before finalising a design or retrofit, it is useful to go through a simple checklist:
- Environment: is the installation exposed to frequent storms, long overhead lines, industrial switching or sensitive processes? If so, surge protection is highly advisable.
- Critical loads: are there servers, automation systems, medical equipment, security systems, refrigeration or other essential equipment? Prioritise their protection.
- Board layout: is there enough space on the DIN rail for SPDs and overvoltage relays? Can wiring to busbars and earth be kept short and tidy?
- Coordination: are type 1, 2 and 3 devices selected so that their energy handling and voltage limitation characteristics complement one another?
- Socket-level protection: in IT areas and workstations, is it sensible to add multi-socket extensions with integrated surge protection from the ION range to protect individual devices?
- Documentation and labelling: are devices clearly identified and included in the installation’s diagrams and maintenance procedures?
14) Conclusion: from theory to a coherent protection strategy
Transient and permanent overvoltages are different phenomena, but both are predictable and manageable when they are taken into account from the design stage of a low-voltage installation. Transient surges require a coordinated chain of SPDs (type 1–2–3) from the origin to the most sensitive loads. Temporary and permanent overvoltages call for monitoring and disconnection by means of dedicated relays or combined protection devices.
Beyond individual components, the key is to create a consistent system: enclosures suited to the environment, well-organised and clearly wired boards, multi-socket extensions with local surge protection for sensitive equipment, and a maintenance plan that includes periodic checks and documentation. Solutions such as Solera’s modular surge protectors, ION multi-socket extensions with surge protection and Indubox industrial enclosures and panels provide a practical base for building this strategy into real-world installations.
By understanding how overvoltages arise, what impact they have and which protection devices are available, designers, installers and maintenance teams can significantly reduce failures, extend equipment life and improve safety in low-voltage systems, from domestic properties to complex industrial sites.