Surge Protection for Life Safety and Data Systems – Overview

Surge protection is critical for life safety systems and associated data/communication networks, especially when cabling spans multiple buildings. Transient overvoltages (“surges”) from lightning strikes or electrical switching can damage sensitive equipment and disrupt essential services. In multi-building facilities, differences in earth potential and longer cable runs increase surge risks. Effective surge protection ensures that fire alarms, smoke control panels, emergency communication systems, emergency lighting, fire-fighting lifts, and critical data links (e.g. IP networks, RS-485 door access) remain operational and safe during transient events. This forms a key part of overall life safety strategy and regulatory compliance in the UK.

Surge Risk in Multi-Building Systems: Surges can enter a building via power supply lines or signal cables. Lightning strikes (direct or nearby) induce high-voltage surges on metallic services like mains power, telephone lines, network cables, or alarm circuits. In a campus or multiple-building setup, a lightning strike on one structure can propagate through interconnecting cables to others, potentially causing equipment failure or malfunctions across safety systems. Even without direct strikes, indirect lightning electromagnetic pulse (LEMP) coupling can induce thousands of volts on long cable runs. Additionally, large inductive loads (e.g. lift motors, generators) can cause switching surges that travel through power circuits. A particular concern with separate buildings is ground potential rise – if lightning hits one building or its earth, a large voltage difference can develop between that building’s earth and others. Any conductive cable between them will attempt to equalize this difference, potentially subjecting equipment on both ends to a severe transient. Without proper protection, such events can disable fire alarm control panels, corrupt emergency communication networks, or even pose shock and fire hazards.

Applications in Life Safety and Data Systems

Many critical systems demand surge protection to ensure continuous operation during transient events:

• Fire Detection and Alarm Systems: These typically span across buildings (for example, a networked fire alarm system in a campus). Surges on mains power or inter-panel communication lines can trigger false alarms or incapacitate the system. BS 5839-1 (fire alarms code of practice) mandates system integrity – a surge must not render the alarm inoperative during an emergency. Protecting fire alarm panels’ mains supply and any data links (e.g. network or detection loop cables between buildings) with SPDs or optical isolation is essential.
• Smoke Control and Ventilation Systems: Smoke extract fans, dampers, and control panels often have motors and control circuits that run between areas. A lightning-induced surge could damage the control unit or actuators, preventing smoke clearance. Surge protectors on power feeds and control signal cables (e.g. between a main fire panel and remote damper motors) help ensure these systems function when needed.
• Emergency Communication Systems: This includes public address/voice alarm (PA/VA or “tannoy”) systems used for evacuation messages, as well as emergency telephones. These systems often rely on amplifiers and speakers throughout a building or across a site. Surges can silence amplifiers or distort communications. Protecting the AC mains supply and any copper data links (audio lines, network connections) is vital. In multiple buildings, using fibre-optic links for audio/data distribution or installing SPDs on copper lines at building entry points is recommended to prevent lightning damage. BS 7671 classifies PA systems used in emergencies as “safety services” requiring surge protection.
• Emergency Lighting: Emergency lighting units (whether central battery systems or self-contained lights) must operate during mains failures. They are typically charged from mains circuits; a surge can blow fuses or damage chargers/batteries. By installing SPDs on emergency lighting supply circuits, the risk of a transient overvoltage knocking out lighting is reduced. Standards like BS 5266-1 and BS EN 1838 require reliable operation for defined durations, which implies protecting lighting circuits from power disturbances.
• Fire-Fighting and Evacuation Lifts: Lifts designated for use during firefighting or evacuation have dedicated power supplies (often backed up by generators). The lift’s control panels and motors are sensitive to surges – for instance, when a building with a lift is struck by lightning or if there’s a surge when switching to generator power. Transient suppression on the lift’s supply panels (and control signal interfaces) prevents nuisance tripping or damage. In multi-building sites, if a fire-fighting lift’s status or controls report back to a fire panel in another building, those communication lines should also be surge-protected or galvanically isolated.
• IP Networks and Surveillance (CCTV): Modern life safety and security systems often ride on the IP network – e.g. CCTV cameras for situational awareness, access control system servers, or VoIP emergency phones. Copper Ethernet cables between buildings are vulnerable to lightning-induced surges and differences in earth potential. It is strongly recommended to avoid running copper data cables between separate buildings; fibre-optic cable is preferred as it is non-conductive and immune to lightning surges. If copper must be used (such as CAT6 for a short link), then at minimum install RJ45 surge protection on each end and ensure both buildings share a good equipotential earth bond. Even within one building, network switches or camera power injectors can be damaged by transients, so Category 6 surge protectors or PoE surge protectors are used for critical devices.
• Access Control and Alarm Signaling (RS-485, etc.): Many access control systems use RS-485 or other low-voltage communication buses to connect door controllers, sensors, and panels. In a campus or multi-building scenario, these cables often traverse outdoors or between building MDF/IDF rooms. RS-485 lines are typically differential and some devices include basic transient suppressors, but a nearby lightning strike can induce high currents that far exceed those protections. To protect electronic door locks and controllers, options include using galvanic isolation modules in the RS-485 line or converting segments to fibre. Galvanic isolators insert an isolation barrier (optical or transformer coupling) that breaks direct electrical continuity, preventing dangerous surge currents from flowing between buildings. For example, an isolated RS-485 repeater can protect controllers in one building from a surge coming in on a cable from another building. Additionally, surge arrestors designed for data lines (SPDs for telecom/ signalling circuits) can be installed at cable entry points to clamp any high voltages to earth.

Lightning Protection Zones (LPZ) and Coordinated SPD Deployment

BS EN 62305 (Protection Against Lightning) introduces the concept of Lightning Protection Zones (LPZ) to manage lightning surge energy and electromagnetic effects inside structures. The premise is to divide the installation into zones of decreasing surge exposure, with Surge Protective Devices (SPDs) at the boundaries to progressively reduce a large transient (often thousands of volts) down to a safe level for equipment. Key LPZ definitions (per BS EN 62305) are:

• LPZ 0A: The zone outside the structure that is fully exposed to lightning-direct strikes are possible and the full lightning current and electromagnetic field may be present. This would be, for example, a roof or an external area not protected by any air termination system.
• LPZ 0B: An external zone where direct lightning flash is prevented (e.g. under a lightning rod or meshed air termination system) but still subject to the full lightning electromagnetic field. In LPZ0B, no direct strike occurs, but partial lightning currents and intense electromagnetic fields are present. For instance, the space immediately under a lightning-protected roof overhang or just outside an entry point could be LPZ0B – protected from direct hits but not from the field or currents conducted via cables.
• LPZ 1: The first internal zone within the building. Here there is no direct lightning strike and some shielding reduces the electromagnetic field. However, conductive services entering from outside may carry a portion of lightning current (induced or conducted). Thus, surge currents are “partial” and the magnetic field is damped compared to outside. Typically, LPZ1 is the area right after the service entrance – for example, inside the main distribution board room where incoming cables from LPZ0 transition indoors. Installing a suitably rated SPD at the entry bond (boundary of LPZ0 to LPZ1) is critical to shunt the bulk of surge energy to earth at this point.
• LPZ 2 (and higher): Deeper internal zones where surge effects are further mitigated. In LPZ2, any residual lightning surge is further limited (often by additional SPDs or filtering), and the electromagnetic field is highly damped. Sensitive equipment should ideally reside in LPZ2 or LPZ3, where the environment is compatible with their withstand voltage. For example, an equipment room with an extra local surge suppressor or a Faraday-cage enclosure for critical electronics can be considered LPZ2/3. LPZ 2+ simply implies any higher-numbered zone (LPZ2, 3, etc.) that provides even greater protection – the higher the zone number, the lower the expected surge energy. Each successive zone is created by additional protective measures: e.g. a Type 2 SPD might be installed on sub-circuits at the boundary of LPZ1/LPZ2, and Type 3 SPDs at sensitive equipment between LPZ2/LPZ3. In practice, a coordinated SPD system is deployed: Type 1 arresters at the LPZ0→1 boundary, Type 2 at LPZ1→2, and Type 3 at LPZ2→3. This coordinated arrangement, as required by BS EN 62305-4, ensures the lightning surge is gradually clamped to safe levels before reaching delicate devices.

Surge Protective Device Types (BS EN 61643 & BS 7671 Section 534): Surge protectors are classified by type, relating to their energy discharge capability and installation location. BS 7671 (Wiring Regulations) Section 534 and BS EN 62305-4 both emphasize using the right SPD type at the correct point in the installation for effective protection. The three main categories are:

• Type 1 SPD – “Lightning Current Arresters”: These are heavy-duty surge arrestors designed to safely divert the very high currents from a direct lightning strike. They are tested with a 10/350 µs impulse waveform (simulating a lightning strike). Type 1 SPDs are typically installed at the origin of the electrical installation, e.g. in the main incoming panel where the service cable enters the building (boundary of LPZ0 to LPZ1). They are often called equipotential bonding SPDs because their role is to clamp lightning voltages and bond all incoming conductors (live, neutral, earth) together to the same potential during a strike. For any building with an external Lightning Protection System (LPS) or tall structures at risk of direct strikes (or if overhead supply lines are used), Type 1 SPDs are required at the intake position. In a life safety context, this protects the main distribution board and upstream circuits feeding systems like fire alarms, sprinklers or lifts from massive surges that could otherwise cause immediate failure or fire.
• Type 2 SPD – “Surge Arresters”: These are medium-duty SPDs, tested with an 8/20 µs current impulse, suitable for protection against indirect lightning effects and switching surges. A Type 2 is typically installed downstream of any Type 1 device (or at the origin if no risk of direct strike exists) – for example, at sub-distribution boards, control panels, or the mains boards of smaller buildings. In many commercial installations, the first device at the mains incoming may actually be a combined Type 1+2 unit (covering both roles). Type 2 SPDs limit transient overvoltages to levels safe for most equipment (generally below ~1.5 kV). They are crucial for locations where direct lightning strikes are unlikely but surges from remote strikes or the grid can still enter – e.g. built-up urban areas or sites fed by underground cables. For life safety systems, Type 2 units are used on distribution boards feeding things like fire alarm panels, emergency lighting circuits, smoke control panels, etc., ensuring an indirect surge doesn’t propagate into these critical devices.
• Type 3 SPD – “Equipment Protectors”: These provide the final stage of protection with a much lower clamping voltage, to safeguard sensitive electronics from residual surges. Type 3 SPDs are tested with a combination wave (1.2/50 µs voltage combined with 8/20 µs current) and must have a very low let-through voltage (Up) to protect delicate equipment. They are typically installed close to the equipment they protect – e.g. a surge-protected socket strip for a fire alarm panel or an SPD module within an equipment enclosure. Notably, Type 3 SPDs should only be used in systems that already have Type 1/2 upstream, because they are not designed to shunt large surge currents on their own. In practice, you might find a combined Type 2+3 unit in a panel, or plug-in protectors for specific devices like control room computers, PA system amplifiers, or network switches that are part of safety systems. These guard against any remaining transient after the Type 1 and 2 SPDs, as well as against locally generated surges (for example, the on-off switching of a lift motor or pump causing voltage spikes).

All three types work together as a coordinated SPD system. For instance, in a hospital with multiple buildings, the main incoming switchboards in each building have Type 1+2 SPDs to handle the bulk of a surge, while each fire alarm panel or server rack might have a Type 3 point-of-use protector installed. This coordination ensures the energy is progressively clamped and no single SPD is overstressed. Manufacturers test and specify SPDs to be coordination-compatible (especially if mixing brands, care must be taken to ensure they coordinate per BS 7671 534.4.4.5).

Mitigation Methods and Technologies

In addition to the proper selection of SPDs, several other strategies are employed to protect life safety and data cabling between buildings. Often a combination of methods yields the best protection. Below is an overview and comparison of key mitigation measures, and how they apply in life safety scenarios:

• Fibre-Optic Links: One of the most effective protections for inter-building cabling is to eliminate the metallic pathway altogether. Converting critical communication links to fibre optic cables provides complete galvanic isolation between buildings. Fibre cables do not conduct lightning surge currents or ground potential differences, and they are immune to electromagnetic interference. For example, a fire alarm network connecting multiple structures or an IP CCTV feed between buildings should use fibre – this way, even if lightning strikes one building, the surge cannot travel through the fiber to the others. Fibre links are recommended by industry guides for any network or signal line leaving a building; they drastically reduce surge risk (the only consideration is to protect the fiber transceiver equipment’s power supply with SPDs). UK practice (e.g., BS 5839-1 for fire alarms) increasingly encourages use of fibre or wireless links for networking fire panels across sites, precisely to avoid transient issues that copper links face. Summary: Fibre-optic conversion offers the highest surge immunity for data/communications, and is ideal for campus fire and security systems – its main downsides are the need for media converters and power at each end, but these are minor compared to the safety benefit.
• Galvanic Isolation: Where fibre is not feasible, galvanic isolation can be introduced in copper circuits to break the direct electrical connection between buildings. This can be achieved with isolation transformers, opto-couplers, or specialized isolator devices. For instance, Ethernet ports inherently have isolation transformers providing typically ~1.5 kV isolation; RS-485 or telephone line isolator modules can provide 5 kV or more isolation. Galvanic isolation prevents dangerous equalizing currents by ensuring there is no DC continuity – in effect, surge voltages must jump an isolation barrier which greatly attenuates transient energy. An isolated circuit still needs surge diversion to earth, but it will limit the surge that reaches the protected side. In life safety systems, one might use isolating interface units on long sensor or control lines between buildings. Example: An isolation barrier on a door access control line can stop a surge that enters on the external reader cable from frying the internal controller. Similarly, an isolating transformer on a low-voltage power feed to an outbuilding (along with SPD across the secondary) can help decouple lightning-induced transients. Note: While galvanic isolation improves safety and reduces surge impact, it is not an absolute shield – very high lightning voltages can still bridge isolation if not properly rated. Therefore, isolation is best used in tandem with SPDs. Manufacturers often integrate surge suppression in isolated line protectors (e.g. an isolated RS-485 surge protector unit). Galvanic isolation also helps eliminate ground loops and interference, improving system reliability in normal conditions.
• Equipotential Bonding: Proper bonding is fundamental to any surge protection strategy. Equipotential bonding means connecting the metallic parts and earths of different systems so that during a transient event, they rise in potential together, minimizing voltage differences. In practice, for multiple buildings, this could mean bonding the earthing systems of each building with a substantial conductor or via a common earthing network. BS 62305 emphasizes that all external conductive services (power cables, metal pipes, telecom cables) should be bonded to the main earthing terminal at the entry point, often through an SPD if direct bonding is not feasible. By bonding through an SPD (Type 1), the device will conduct surge current to equalize potentials, then block continuous current flow after. For example, if Building A is struck by lightning, its earth potential may shoot up relative to Building B; an equipotential bonding conductor (or SPD between their earthing systems) will conduct the lightning current and prevent a large voltage (and dangerous flashover) between building B’s metalwork and cables coming from A. UK Wiring Regulations (BS 7671) Section 534 note that Type 1 SPDs at service entrances are often termed “equipotential bonding SPDs” for this reason. Additionally, bonding practices include using surge protective bonding for data lines – for instance, running signal cables inside metallic conduit or using cables with an earthed overall screen that is bonded at both ends can help create an equipotential shield around the conductors. However, caution: bonding both ends of a cable shield between buildings can itself create a loop for currents – this is where SPDs on the shield or one-end bonding plus an SPD/isolator on the other end may be used to manage that. In summary, a robust bonding network ensures that when surges occur, current is routed safely to earth and voltage differences are minimized, protecting people and equipment from shock and fire risk.
• Surge Protective Devices (SPDs): As discussed, SPDs are the frontline devices that limit transient overvoltages by clamping the voltage and diverting surge energy to earth. They come in various designs (gas discharge tubes, metal-oxide varistors, spark gaps, etc.), but their application in life safety follows the coordinated approach by type. Type 1 SPDs (often combined with a Main Earthing Terminal block) handle the brunt of lightning currents; Type 2 SPDs at distribution panels further suppress residual surges; and Type 3 SPDs protect the most sensitive endpoints. In addition, there are special SPDs for data/signal lines – e.g. telephone line protectors, co-axial surge arrestors for radio/base station lines, and network cable SPDs. When protecting life safety data links like an alarm communication line, these signal SPDs should be installed in a coordinated way too (typically at the boundary of LPZ0/1 when a line enters a building). Good practice is to install SPDs on both ends of an inter-building copper line: one at each building’s entry point to clamp surges to the local earth. All SPDs must be connected to a low-impedance earth point (typically the building’s earth bar); otherwise their effectiveness is compromised. Regular maintenance and inspection of SPDs is also a part of compliance – e.g. BS 7671 requires that SPDs be tested or visually inspected for any failure indicators during periodic inspections, to ensure continued protection.

The table below summarizes common surge threat scenarios in multi-building life safety installations, along with typical protection measures and examples of their application:

Regulatory Framework and Standards

Several UK standards and regulations provide requirements and guidance on surge protection for life safety and inter-building systems:

• BS 7671 (IET Wiring Regulations), Section 443 & 534: The 18th Edition Wiring Regulations (BS 7671:2018 + A2:2022) explicitly require surge protection for scenarios involving risk to human life and safety services. Regulation 443.4.1 states that “Protection against transient over-voltages shall be provided where the consequence caused by over-voltage could result in: (i) serious injury to or loss of human life, (ii) failure of a safety service…, (iii) significant financial or data loss.” Life safety systems clearly fall under points (i) and (ii), so SPDs must be installed to protect such systems. This effectively makes surge protection mandatory for fire alarms, emergency lighting, fire-fighting lifts, evacuation systems, etc., in most installations. (Previous editions allowed omitting SPDs via risk assessment, but Amendment 2 removed the risk assessment exemption for these cases.) Section 534 of BS 7671 then gives practical guidance on selecting and installing SPDs to meet these needs. For example, it indicates where Type 1 or Type 2 devices should be used, coordination requirements, and connection methods. An informative Appendix (Appx 16) provides further surge protection application principles. Compliance with BS 7671 ensures that the surge protection measures are correctly integrated into the electrical installation of a building housing safety systems.
• BS EN 62305 (Parts 1-4): This series is the code for Lightning Protection. Part 1 and 2 cover risk assessment and design principles, which determine if a structure needs external lightning protection and/or surge protection. Importantly, if the risk assessment shows the building or its services are at risk (for example, presence of an LPS or overhead lines), BS EN 62305-2 and -4 mandate SPDs on incoming services. “Where structural LPS is required, Type 1 SPDs are always required for metallic services (power, data, etc.) entering the structure”. Even if an LPS isn’t required, the standards say to fit SPDs if there’s risk of indirect lightning surges – e.g. Type 1 for overhead-fed lines or Type 2 for underground-fed lines into the building. Part 4 of BS EN 62305 specifically deals with electrical and electronic systems protection. It introduces Lightning Protection Zones and the concept of a “coordinated SPD system” as discussed above. Adhering to BS EN 62305-4’s principles (often achieved by following BS 7671 Section 534 recommendations, since they align) is crucial for complex sites – it ensures that SPDs are placed correctly to correspond with LPZ boundaries and that they have adequate rating to the Lightning Protection Level (LPL) needed for the site. For example, a site with LPL I (highest lightning severity) will choose SPDs with higher impulse current ratings compared to a site with LPL III.
• BS 5839-1 (Fire detection and fire alarm systems): BS 5839-1:2017 is the code of practice for fire alarm system design and installation. While its primary focus is on detection coverage, reliability, and resilience (like battery backup duration), it does touch on electrical supply quality and integrity. The standard requires that the mains supply to the fire alarm has an isolator that’s reliable and that the system isn’t prone to false alarms or failures due to power issues. In practice, this means the fire alarm’s mains circuit should be robust – installing an SPD on the fire alarm panel’s supply circuit is strongly recommended (and would be required under BS 7671 anyway as a safety service). BS 5839-1 also discusses networked fire alarm systems (multiple panels across buildings); one of the recommendations is that where networks exit a building, protection against surges or faults should be in place (either by isolation or by using methods that inherently prevent surges, like fibre optics, or by surge suppression on those lines). Although BS 5839-1 may not explicitly use the term “surge protector,” it implies that all circuits essential to the system’s operation (including interconnections) must be suitably protected from foreseeable electrical hazards. Designers of fire alarm systems cross-reference BS 7671 for guidance on transient overvoltage protection to meet the general requirements of BS 5839-1 on system reliability.
• BS 8519 (Selection and installation of fire-resistant power and control cable systems for life safety and fire-fighting equipment): BS 8519:2020 provides guidance for ensuring power and control cabling for critical systems (like fire-fighting lifts, sprinkler pumps, smoke control panels, etc.) will survive and operate during a fire for a specified period (e.g. 30, 60, 120 minutes depending on category). While this standard is about fire resistance of cables and redundancy of power supplies, surge protection interfaces with it by preserving the functionality of those power/control circuits in the face of transient events before a fire emergency occurs. For example, BS 8519 recommends dual redundant supplies or paths for some systems – both should be surge-protected to avoid a single transient taking out both paths. It also emphasizes security of supply, noting that mains supply cables for life safety systems should ideally enter directly from an intake position dedicated to those systems. In practice, at that intake location one would install a Type 1 or Type 2 SPD to protect the circuit. Additionally, if control cables run between fire control centers in different buildings (say a smoke control panel sending a trigger to a fan in another block), BS 8519 would call for fire-rated cable, and one should also ensure those cables have surge protection (so they are not only fire resistant but also lightning resistant). Compliance with BS 8519 thus indirectly requires addressing surge risks – a transient voltage spike could otherwise incapacitate an otherwise robust fire-resistant circuit.
• Other Standards and Codes: Various other documents complement the above. For instance, BS EN 62305-3 (physical damage and life hazard) reinforces bonding requirements and separation distances to prevent dangerous sparking – which ties into using SPDs or isolating gaps to bond systems without flashover. BS EN 61643 series covers product standards for SPDs (ensuring the devices used are tested and rated properly for use). Building Regulations (Approved Document B) stipulate that emergency systems must have adequate power supplies; a surge event is effectively a power quality issue, so it falls under maintaining that continuity. There are also industry guides (FIA, IET guidance notes, etc.) that provide best practices, such as using coordinated surge protection for any electronic safety system spanning multiple structures and ensuring maintenance/testing of SPDs as part of routine service of life safety systems. In summary, UK regulations create a framework where surge protection is not optional when it comes to life safety and critical data systems – it is a required aspect of design to safeguard against lightning and switching transients, thereby preserving the functionality of systems that protect lives. By following these standards, engineers and installers help ensure that a lightning storm or a power surge does not compromise the very systems intended to keep occupants safe during emergencies.