When purchasing a surge protector for your home, you need to consider its installation location. Surge protectors are typically connected in parallel behind the main power supply and main circuit breaker, positioned as close as possible to the protected object. An incorrect installation location can significantly reduce the protective effect of the surge protector, and different types of SPDs are required for various surge protection scenarios.
What is a surge?
When the voltage or current flowing through a circuit suddenly increases beyond the range that the power system can withstand, this phenomenon is called a surge. There are many causes that can induce surges, mainly including external lightning strikes, grid switching, and the startup or shutdown of internal high-power equipment, as well as electrostatic reactions. External surges occur less frequently but typically have characteristics of high energy and destructive power. They can propagate indoors through various pathways and cause severe damage to sensitive electronic components.
Overhead transmission line :
Overhead transmission lines exposed outside buildings and extending over long distances are the most common external surge propagation pathways. When lightning directly strikes a transmission line, transient overvoltage rapidly propagates along the wire to both ends, entering the building’s main distribution panel through the power line entrance and causing severe damage. Even if not directly struck by lightning, the electromagnetic field generated by lightning can induce surge voltage on nearby overhead transmission lines.
Signal lines and communication lines (Ethernet, telephone lines, coaxial cables) :
Signal lines and communication lines can also induce surge voltage due to the high-energy electromagnetic field generated by lightning discharge.
At the same time, because data transmission lines usually have relatively thin cables and sensitive device interfaces, their ability to withstand surges is low. Even minor fluctuations can lead to serious consequences such as data loss or hard drive damage.
Grounding system reverse conduction:
When the external lightning rod of a building is struck by lightning, the direct lightning surge current is discharged to the ground through the grounding wire, causing a sharp rise in ground potential near the grounding point. A potential difference forms between different grounding points and is conducted back into internal equipment via the grounding conductor.
SPD Working Principle/Classification
Surge Protective Device, abbreviated as SPD, is a device used to protect power systems from surge damage. When transient overvoltage occurs in the circuit, the surge protection device reduces its resistance value through core components such as MOV or GDT, discharges surge current and suppresses overvoltage, thereby protecting downstream load equipment.
According to the provisions of IEC 60634 and IEC 62305, surge protective devices are classified into three types based on installation location and surge protection level:
- Type 1 SPD: Surge protective devices capable of withstanding a 10/350 μs waveform impact (simulating lightning surges). Primarily used to handle external high-energy surges caused by lightning strikes or power grid switching.
- Type 2 SPD: Surge protective devices capable of withstanding an 8/20 μs waveform impact. Mainly used to suppress induced lightning surges and transient overvoltages generated within building distribution systems.
- Type 3 SPD: Surge protective devices capable of withstanding combined waveforms (1.2/50 µs voltage combined with 8/20 µs current) impacts. Primarily used for providing terminal fine protection for sensitive electronic equipment.
Graded protection and the concept of lightning protection zones
When a building is struck by lightning, direct lightning surges can propagate indoors along various conductors, and installing an surge protective device at a single point cannot meet surge protection requirements. Additionally, when surge current passes through the Type 1 surge protector installed at the power entry point, if there are no Type 2 and Type 3 SPDs to further clamp residual voltage in the circuit, there remains a risk of overvoltage within the electrical system. A tiered surge protection strategy can significantly enhance the reliability and effectiveness of the building’s internal surge protection system.
In the graded surge protection system, the installation locations of different types of SPDs are determined by lightning protection zones (LPZ). Lightning protection zones refer to areas within a building’s internal structure divided based on risk levels associated with lightning electromagnetic pulses (LEMP), where surge protective devices of corresponding grades need to be configured at the boundaries between different LPZs.
| Types of SPD | Type 1 | Type 2 | Type 3 |
| LPZ boundry | LPZ 0 → 1 | LPZ 1 → 2 | LPZ 2 → 3 |
| Test Waveform | 10/350 μs | 8/20 μs | 1.2/50 μs & 8/20 μs (Combination waveform) |
| Key Parameters | Iimp: 7–50 kA | In: 20 kA Imax: 20–40kA | At Uc = 255 V, the Uoc value is 6 kV. |
| Core Protection Componets | Graphite,MOV,GDT | MOV,GDT | MOV,GDT,TVS |
| Voltage Protection Level (Up) : | At Uc = 275 V, the Up value is ≤ 1.5 kV. | ||
| Installation Location | Installed at the main distribution board (incoming service entrance) | Installed at sub-distribution boards or floor panels | Installed directly in front of sensitive equipment (such as medical devices and servers) |
First floor: Main building entrance/Main distribution panel (LPZ 0→1)
The cascading surge protection strategy is mainly divided into three stages, where the energy of external high-energy surges is gradually reduced after passing through each level of SPD, ensuring that the voltage in the final circuit remains below the impact tolerance voltage of sensitive electronic equipment. It is akin to making coffee, where the coffee liquid undergoes three rounds of filtration—through a metal filter, cloth filter, and paper filter—each time removing finer coffee grounds to ultimately produce smooth and clear coffee. Severe transient events are progressively mitigated through three levels of surge protection treatment, reducing them to safe levels before reaching load equipment.
The first stage of the cascaded surge protection strategy is surge protection at the power supply entrance of the building, located at the LPZ 0→1 boundary. The power supply entrance is where electricity enters the building from the public grid and serves as an entry point for high-energy surges caused by severe transient events (such as lightning strikes or public grid switching). Therefore, surge protection devices at this location must have the capability to handle high-energy surges, suppress overvoltage before external surges enter the internal distribution system, and protect the entire electrical system from damage caused by external high-energy surges.
- Installation location: Connected in parallel before the main circuit breaker and linked to the secondary side of the power supply transformer.
- Surge protective device Type: Type 1 SPD
- Important Note: Type 1 SPD (10/350 µs) can handle surge energy that is 10–20 times greater than that of Type 2 SPD (8/20 µs). If a proper surge protection device (Type 1 surge protector) is not installed at the power entry point and only a Type 2 surge protection device is used, during direct lightning surges (10/350 µs), the Type 2 SPD will fail immediately due to its inability to withstand excessive surge energy. Therefore, a Type 2 surge protector cannot replace a Type 1 surge protector.
Second layer: Sub-distribution panel/branch circuit (LPZ 1→2)
The second stage of the cascading surge protection strategy is surge protection at the distribution panel, located at the LPZ 1→2 boundary. The distribution panel distributes power to various branch circuits, supplying electricity to different areas of the building. Surge protection devices at the distribution panel are primarily used to handle residual voltage after Type 1 SPD and switching transient surges generated within the power system.
Since the surge protection level of Type 1 surge protector is generally higher than the withstand voltage of internal system equipment, the distribution panel’s surge protection device needs to further clamp the residual voltage in the circuit to ensure the safety of critical electronic equipment. You can imagine it as coffee grounds: after being filtered with water for the first time, only large particles are removed, affecting taste; only through further filtration can clear coffee liquid be obtained. Meanwhile, low-energy surges within a building interfere with equipment far less intensely than external surges like lightning strikes but occur more frequently. If transient surge interference of this type is not promptly addressed with surge protection, it may lead to reduced performance and shortened lifespan of protected devices, resulting in costly repairs or replacements.
- Installation location: Distribution panel
- SPD Type: Type 2 SPD
- Important note: Type 2 SPD is typically installed downstream of Type 1 surge protector or at the distribution panel. Type 1 SPD is used to handle high-energy external surges, while Type 2 surge protection device is used to handle internal surges. The combination of both surge protection devices provides comprehensive surge protection for the electrical system.
It is particularly important to note that when Type 1 SPD and Type 2 SPD are installed in series, the Type 1 SPD must act first to capture most of the surge energy. Therefore, it is necessary to lay a sufficiently long cable between the Type 1 surge protector and Type 2 surge protection device to ensure the correct activation sequence of the surge protection devices. According to IEC 61643-12 standard, a minimum cable distance of at least 10 meters is required between Type 1 surge protective device and Type 2 surge protector in cascade coordination strategies for SPDs.
Third layer: Sensitive electronic equipment terminal (LPZ 2→3)
The final stage of the cascading surge protection strategy is surge protection for terminal sensitive electronic equipment, located at the LPZ 2→3 boundary. This stage primarily involves handling low-energy surges at the front end of sensitive equipment to maintain device performance, prevent data corruption and other potential system terminal issues, thereby enhancing the overall reliability and lifespan of the electrical system.
Even after correctly installing surge protectors at the service entrance and each branch distribution panel, the voltage reaching terminal electronic devices such as computers, televisions, industrial control equipment, and household appliances may still exceed their safe tolerance range. Precise localized surge control is needed for relatively small low-energy surges to provide ultimate protection for sensitive electronic devices.
- Installation location: Near or within important or sensitive individual equipment
- SPD type: Type 3 SPD
- Important note: Type 3 SPD cannot be installed independently in the circuit; it must be used under the condition that a Type 2 SPD is equipped upstream. This is because the maximum discharge capacity of Type 3 SPD is lower than the energy of low-energy transient surges untreated upstream. Without a Type 2 SPD to pre-process most surge energy, the Type 3 surge protector will be damaged by surge energy exceeding its capacity and fail to protect load equipment.
- Additionally, when installing a Type 3 SPD, attention should also be paid to ensuring that the wire length between it and the upstream Type 2 SPD exceeds 10 meters.
Graded protection strategies in different application scenarios
The sources of surges in the electrical systems within buildings vary across different scenarios, and the sensitivity of internal equipment to surges also differs. Therefore, to establish a more comprehensive surge protection system, it is necessary to formulate targeted graded surge protection strategies.
Home scenario
Modern residential internal electrical systems typically use parallel circuits, which are relatively simple in structure and usually include a main distribution panel, several branch circuits, and terminal electronic devices. In household scenarios, surge protection mainly targets sensitive electronic devices such as televisions and computers.
First Level Protection (Main Distribution Box)
- Installation Location: At the residential main distribution box
- SPD Type: Type 1+2 SPD (in areas prone to frequent lightning or using overhead transmission lines) or Type 2 SPD (residential areas using underground cables with a well-established external lightning protection system)
- Purpose: Acts as the first filter to block most external high-energy surges from entering the indoor distribution system.
Second-level protection (terminal equipment)
- Installation location: Front end of sensitive terminal electronic equipment
- SPD type: Type 3 SPD
- Purpose: Provide terminal surge protection for expensive electronic equipment.
Business and industrial settings
The internal structure of electrical systems in commercial complexes and factories is more complex, and the economic losses caused by equipment downtime due to surge phenomena are higher. Additionally, frequent transient events triggered by the start-up and shutdown of high-power equipment (such as elevators, air conditioning fans, industrial motors, etc.) in commercial and industrial applications pose a significant threat to the operational stability of electrical systems, necessitating comprehensive three-level coordinated surge protection.
First level of protection (main distribution room/main power supply inlet)
- Installation location: At the main low-voltage distribution cabinet of the building (secondary side outlet of the power supply transformer)
- SPD type: Type 1 SPD
- Purpose: Discharge most external high-energy surge energy
Second-level protection (distribution boxes on each floor / distribution cabinets for critical equipment)
- Installation location: At the distribution room on each floor or at the distribution cabinet in sensitive electronic equipment areas
- SPD type: Type 2 SPD
- Purpose: To handle residual voltage from external surges processed by Type 1 SPD and internal switching transient surges
Third-level protection (Precision Equipment Terminal)
- Installation location: Front end of precision electronic equipment (e.g., PLC, inverter, etc.)
- SPD type: Type 3 SPD
- Purpose: Provide terminal surge protection for critical equipment at the point of use.
Photovoltaic and Renewable Energy Systems
Photovoltaic systems and renewable energy systems are typically built in open areas, directly exposed to lightning environments, with a higher probability of being struck by direct lightning and experiencing induced surge. Additionally, since photovoltaic systems simultaneously have a DC side (photovoltaic array side) and an AC side (inverter AC output side), the tiered surge protection strategy needs to address the risk of surges on both sides.
DC-side surge protection (Photovoltaic array side)
- Installation location: Photovoltaic panel combiner box / DC input cabinet of inverter / Energy storage input cabinet
- SPD type: Dedicated DC surge protector (FLP-PV1000-S Type 1+2 PV SPD)
- Purpose: Prevent equipment damage and system downtime
Surge protection on the AC side (inverter AC output side)
- Installation location: Inverter AC output terminal
- SPD type: AC surge protector (FLP25-275/4S)
- Purpose: To protect the inverter from transient overvoltage and grid faults.
SPD installation in special scenarios
In areas with high requirements for power supply continuity, a stricter graded surge protection strategy needs to be adopted.
Data center
The data center houses servers, storage devices, and other precision electronic facilities that are highly sensitive to voltage fluctuations, requiring the implementation of a comprehensive tiered surge protection system.
- First layer: Install Type 1 SPD at the main incoming line (transformer/distribution room).
- Second layer: Install Type 2 SPD at the UPS output side/precision distribution cabinet (PDU) incoming line.
- Third layer: Install Type 3 SPD at the rack power distribution unit/server power supply endpoint.
- Fourth layer: Install signal-type SPD (Signal surge protector FRD4-24) at network and communication lines (Ethernet, optical-electrical conversion interface).
Communication base station
With the development of modern communication technology, communication interruptions have a significant impact on users’ daily lives. Communication base stations are often built at high altitudes, exposed to high-frequency lightning risks. Therefore, to ensure the continuous and stable operation of communication networks, the communications industry generally adopts a comprehensive surge protection solution of “power protection + signal protection + grounding protection.”
- First layer: Install Type 1 or Type 1+2 SPD at the AC power input.
- Second layer: Install Type 1+2 DC SPD or Type 2 DC SPD in the DC power supply system.
- Third layer: Install coaxial SPD at the RF feed line.
- Fourth layer: Install SPD for PoE on network communication lines.
- Special requirements: The grounding resistance of the base station must be strictly controlled (usually less than 1Ω–5Ω), and the grounding wire of the installed SPD should be as short as possible to maximize surge protection effectiveness.
Hospital
Surge protection within hospital areas is crucial because medical facilities are often expensive, and the equipment is highly sensitive to voltage fluctuations. System downtime could directly threaten patients’ lives.
- First layer: Install Type 1 SPD at the hospital’s main power distribution system.
- Second layer: UPS and diesel generator system: Install Type 1 SPD at the input end of the UPS rectifier and between the diesel generator and UPS switching device; install Type 2 SPD at the output end of the UPS inverter.
- Third layer: Install Type 2 SPD at floor or department distribution panels.
- Fourth layer: Install Type 3 SPD at the front end of individual medical equipment.
Installation requirements
After selecting the appropriate installation location, to further enhance the surge protector’s protective effect on load equipment, the following requirements should be met during installation:
Conductor Length
- When connecting the SPD to the grounding system, ensure that the grounding wire is as short and straight as possible. The total connection length between the SPD and the grounding busbar should not exceed 50 cm.
- The SPD should be placed as close as possible to the protected equipment, and its connecting wires should be kept as short as possible, typically recommended to be <0.5m, avoiding loop formation.
- In a cascaded surge protection system, to ensure proper activation sequence of SPDs, the cable length between each level of SPDs should be greater than 10m.
Accurate grounding (grounding system compatibility)
SPD discharges surge currents through the grounding system and suppresses overvoltage. Therefore, the effectiveness of SPD surge protection is directly determined by whether the grounding system is properly connected. Each type of grounding system requires a different SPD configuration to ensure maximum surge protection.
| Earthing system | SPD mode(3-phase) | Uc | N-PE element | Key rules |
| TN-S | 3+1 | 275 V | Required-same | Standard for most lEC commercial/industrial |
| TT | 4+0 | 275-320 V phase; up to 440 V N-PE | Required – higher Uc | Higher N-PE U,essential-standard 275 V fails prematurely under TT fault conditions |
| TN-C | 3+0（L-PEN only） | 275 VL-PEN | Never-shorts PEN conductor | No N-PE element anywhere in TN-C section |
| TNC-S | 3+1 | 275 V | Required-same | Use TN-S-style SPD after PEN split; no N-PE element in TN-C section |
| IT | 3+0（L-PE only） | ≥440 VL-PE | Not applicable | Uc must cover phase-to-earth voltage in first fault condition |
Parallel installation (not series)
The SPD must be connected in parallel to the circuit (i.e., forming a parallel connection with the load). When providing protection, the internal core component of the SPD reduces its resistance to discharge surge currents. Only by being connected in parallel at the front end of the load can it absorb a large amount of surge energy in advance, reduce residual voltage in the circuit, and ensure equipment safety.
Pre-protector
The SPD front end requires the installation of protective devices (such as MCB/MCCB/Fuse). In case of SPD failure, there is no need to cut off the main power supply; the front-end protector will automatically trip, allowing direct maintenance and replacement of the SPD.
Common Installation Mistakes
- Multiple SPDs not unified in potential: Lack of equipotential bonding between SPDs creates potential differences, affecting the overall surge protection performance.
- Inadequate grounding system coordination: High grounding resistance or incorrect grounding connections reduce SPD protection effectiveness.
- Insufficient cross-sectional area of grounding wires: The wire’s cross-sectional area determines its ability to divert surge currents; if too small, it generates resistance within the conductor, producing heat during surges and posing a fire risk.
- Using single-phase SPD in a three-phase system: In a three-phase system subjected to surges, a single-phase SPD can only protect one phase circuit from surges, leaving the other two phases vulnerable to surge current attacks.
- Neglecting SPD monitoring and status indication functions: The SPD indicator window shows operational status (green: normal operation; non-green: device failure). Failure to check the indicator window regularly may result in faulty SPDs remaining in the circuit without providing surge protection.
LSP: More Than an SPD Manufacturer – Your Trusted Partner in Surge Protection
Since 2010, LSP has been dedicated to the research, development, and manufacturing of Surge Protective Devices (SPDs), providing customers worldwide with safe, reliable, and long-lasting surge protection solutions. We understand that a single lightning strike or surge event can lead to equipment damage, system downtime, and significant financial losses. That is why every LSP product is designed with reliability, stability, and performance at its core.
To ensure industry-leading product quality, LSP carefully selects premium raw materials and key components from trusted global suppliers. Combined with a strict quality management system, every stage of production—from incoming material inspection to final product testing—is rigorously controlled. This ensures that every SPD delivered to our customers provides dependable protection and consistent performance throughout its service life.
Beyond product quality, we are committed to the success of our customers’ projects. Whether you require standard products, OEM manufacturing, or ODM customization, our team responds quickly to help shorten project lead times and enhance your competitiveness in the market. In addition, we provide certification support, technical consultation, and comprehensive after-sales service, helping customers reduce both procurement risks and operational risks.
Over the years, LSP surge protection solutions have been widely applied in photovoltaic power generation, electrical distribution systems, industrial automation, telecommunications networks, and commercial buildings. Our products help safeguard critical equipment and ensure the reliable operation of electrical systems around the world.
Conclusion
The effectiveness of surge protection is determined not only by proper selection but also by the appropriate installation location and whether a reasonable graded protection strategy is adopted. External high-energy surges can enter indoor electrical systems through various pathways, and installing only one Type 1 SPD at the power inlet cannot provide sufficient surge protection.
At the same time, the sensitive electronic equipment within the system has a low surge withstand voltage, meaning even minor voltage fluctuations in the circuit can damage these devices and reduce their lifespan. Therefore, even after installing Type 1 SPD at the power input terminal, the residual voltage from direct lightning surges still poses a threat to sensitive electronic equipment in the circuit.
Therefore, a comprehensive surge protection system can minimize the risks caused by surges to the greatest extent, ensure the safe and stable operation of electrical equipment, reduce system downtime losses, and extend the lifespan of the entire electrical system.
FAQ
Does it matter where a surge protector is installed in a panel?
It is very important. The surge protector must be installed as close as possible to the main circuit breaker in the distribution panel and positioned after the main circuit breaker. This is because an increase in wire length will generate additional inductance in the circuit, leading to higher residual voltage and causing damage to load equipment.
Where is the best place to put a surge protector?
The installation location of the SPD depends on specific surge protection requirements: for instance, to counter external high-energy direct lightning surges, Type 1 SPD needs to be installed at the main distribution panel inside the building. LSP will provide you with the best surge protection strategy.
Do SPDs affect the electricity bill?
Installing an SPD in the circuit will not affect electricity costs because the SPD needs to be installed in parallel within the circuit, and under normal conditions, its internal core components are in a high-resistance state. The current allowed to pass through is negligible, so it does not incur additional electricity expenses.
Why is SPD selection different for TNS,TN-C,TNC-S,TT and IT systems?
The surge protector discharges surge current through the grounding system to control circuit voltage, so a proper grounding system affects the effectiveness of surge protection. Different grounding systems have varying neutral lines, protective ground lines, and grounding methods, thus requiring different SPDs.
What happens if SPD is installed incorrectly?
The main function of the SPD is to suppress overvoltage in advance when a surge occurs in the circuit and keep the circuit voltage within a safe level. Improper installation may reduce surge protection effectiveness or even cause SPD failure, leading to potential safety hazards.
