In industrial power distribution systems, many engineers focus on a key issue: how should surge protection for the Service Entrance be configured? Since this location is directly connected to the grid and withstands the highest energy surge impacts, Type 1 SPD is typically required as the primary level of protection for the system.
What is a Type 1 surge protector?
Type 1 SPD (Surge Protective Device) is an electrical safety protection device specifically designed to prevent and limit damage from external surges (mainly lightning surges) to electrical systems and equipment at the service entrance of a building.
According to the IEC 61643-1 international standard, Type 1 SPD is defined as: “A device capable of withstanding a standard lightning impulse waveform of 10/350 μs, tested at Class I level (required to withstand at least 15 instances of 10/350 μs impulses), with a rated impulse current (Iimp) typically ranging from 5kA to 20kA, installed between the power supply entry point and the main distribution system.”
Physical working principle of Type 1 SPD:
- Inductive response — When the surge voltage exceeds the set response threshold (typically 500-1000V), the discharge gap inside the protector is broken down.
- Rapid diversion — A low-resistance path is formed, directing the surge current directly to the grounding line (PE/GND) instead of flowing into the building’s electrical system.
- Energy absorption — Part of the energy is absorbed through metal oxide varistors (MOVs) or other nonlinear components while limiting voltage clamp (protection level Up).
- Residual voltage limitation — Even during current diversion, the voltage across both ends of the protector is restricted within an acceptable range (typically 1.5-2.5kV).
Why Type 1 SPD installed at the Service Entrance?
The path of surges entering the building from the power grid
Three main entry paths of surge:
Pathway 1: Directly entering through the power supply line (most common, most dangerous)
Ground lightning strikes or nearby power distribution lines are hit → High voltage waves travel along the power line (at near light speed) → Enter the building’s service entrance (before the meter) → Directly impact the interior of the main distribution box through the main incoming line → If there is no Type 1 SPD, surges may:
- Break down main circuit breaker contacts
- Melt insulation layers of incoming cables
- Impact all Type 2 SPDs connected to the main distribution box (causing cascading failure)
- Spread to all downstream branch circuits
Path 2: Through the common grounding line and ground loop (often overlooked)
Surges may disperse through earth currents, causing high surface potential to affect the building’s grounding electrode, resulting in dangerous potential differences between equipment in multiple rooms.
Path 3: Through other metal conductors entering the building (metal pipes, metal frames)
Although this path can be minimized through lightning protection design, once it occurs, the equipotential bonding and diversion capability of Type 1 SPD at the Service Entrance serve as the final line of defense.
Consequences of not having Type 1 SPD:
100% surge energy → directly enters the main distribution box → no prior reduction, all Type 2 SPDs simultaneously subjected to 100% impact → collective failure of Type 2 SPDs (their design capacity is far below the 10/350 μs impact) → surge continues to propagate to all downstream circuits → large-scale equipment damage
The overall protective effect on downstream equipment
The role of Type 1 SPD at the Service Entrance is not just to “protect the main distribution box itself”—it creates a protected environment for all equipment within the entire building.
Five Layers of protection:
Layer 1: Protection of the main distribution box
- Protect the main circuit breaker from surge melting
- Protect the main incoming cable from breakdown
- Protect the busbars and contacts inside the distribution box from arc burning
- Prevent all Type 2 SPDs connected to the main distribution box from being instantly destroyed
Layer 2: Protection of Branch Circuits
- After the surge is attenuated, the impact on cables and circuit breakers in branch circuits is significantly reduced.
- Type 2 SPD can function effectively (instead of being overloaded).
- Wiring and junction boxes within branch circuits are less likely to be damaged.
Layer 3: Protection of terminal equipment
- Lighting fixtures, switches, sockets → Prevent direct breakdown
- Air conditioners, pumps, motors and other high-power equipment → Prevent winding burnout
- Electric water heaters, ovens and other heating devices → Prevent internal short circuits and fire risks
Layer 4: Protection of sensitive electronic equipment
- Computers, printers, servers → Type 3 SPD can effectively protect them from being overwhelmed by surges
- Security systems, controllers → Prevent control logic from being damaged
- Communication devices, WiFi routers → Maintain network connection reliability
Layer 5: Protection of Personal Safety
- Prevent fires caused by equipment failure
- Avoid the risk of electric shock (insulation damage caused by surges)
- Prevent explosion risks (some equipment may explode when hit by surges)
| Condition | With Type 1 SPD | Without Type 1 SPD |
| Main distribution panel | Fully protected, no damage | Main breaker contacts may melt and fail to disconnect the circuit |
| Main incoming cable | Insulation remains intact | Insulation breakdown in multiple points, increased fire risk |
| Type 2 SPD | ~95% survival rate, continues operating | Most units fail simultaneously, protection chain is broken |
| Building electrical system | Normal operation | Partial or multiple area outages and instability |
| Household appliances | Fully protected | 50–80% damage rate (refrigerators, air conditioners, TVs, etc.) |
| Computers / servers | No damage | 80–95% damage rate (high risk of data loss) |
| Personal safety | Well protected | Fire or electric shock risk |
The key difference between Type 1 SPD and Type 2 SPD
Although Type 1 SPD, Type 2 SPD, and Type 3 SPD are all SPDs, their design purposes, operating principles, and application scenarios are completely different.
Standard Impact Waveform and Grade
| Dimension | Type 1 | Type 2 | Type 3 |
| Standard waveform | 10/350 μs | 8/20 μs | 8/20 μs |
| Test level | Class I (15 impulse tests) | Class II (20 impulse tests) | Class III (20 impulse tests) |
| Typical Iimp | 5–20 kA | 3–10 kA | 1–5 kA |
| Single surge handling capability | Very high (designed for single or limited surges) | Medium (designed for multiple surges) | Low (designed for small, frequent surges) |
Installation location and protection range
| Location | SPD Type | Standard Waveform | Protection Scope | Standard Requirement |
| Service Entrance | Type 1 | 10/350 μs | Entire building system | IEC 61643-1 |
| Main panel (load side) | Type 2 | 8/20 μs | Branch circuits | IEC 61643-1 |
| Near terminal equipment | Type 3 | 8/20 μs | Single equipment | IEC 61643-1 |
Energy bearing and failure characteristic
- Type 1: Strong single carrying capacity, designed to withstand 1-2 full lightning strikes.
- Type 2: Can withstand 20-50 times of 8/20 μs surges, with gradual aging.
- Type 3: Can endure dozens to hundreds of small surges, low-energy design.
Essential differences in application scenarios:
- Type 1 must be used for: Service entrances of buildings in all lightning-prone areas, and entrances directly connected to outdoor power distribution lines.
- Type 2 is recommended for: Load side of main distribution boxes, branch distribution panels, secondary side of transformers.
- Type 3 is recommended for: Areas near high-value equipment, sensitive control systems, as supplementary protection to Type 2.
In most cases, Type 1 SPD, Type 2 SPD, and Type 3 SPD are used in combination.
Reason 1: Surges have multiple sources
Source A – External lightning (entering from the Service Entrance) → Captured and diverted by Type 1
Source B – Network surges (generated within branch circuits)
Example: Air conditioner startup → Induced surge
Example: Transformer switching → Switching surge
These are generated within branches, and Type 2 can intercept them at branch locations.
Source C – Multiple distribution points within a building (large buildings, factories)
Example: Distribution panels on different floors
Example: Sub-panels in different areas
Type 2 provides localized protection at each distribution point.
Reason 2: Surge attenuation is gradual and requires multi-layer protection.
Limitations of Type 1 alone:
Surge enters (10kA) → Type 1 diversion → Residual surge enters the main distribution box → Spreads to all branches → Expensive equipment (e.g., servers) may still be damaged.
In contrast, with Type 1 + Type 2:
Surge enters (10kA) → Type 1 diversion (9.5kA) → Residual surge (0.5kA) enters the main distribution box → Type 2 further diverts (0.4kA) → Surge reaching equipment (<0.1kA) → Equipment completely safe
How to Choose the Best Type 1 Surge Protector
Impulse current capability (Iimp)
Iimp is the most important parameter of Type 1 SPD. Iimp (Impulse Current) is the rated value of the 10/350 μs waveform impulse current that Type 1 SPD can withstand.
Key understanding:
Iimp = Maximum repetitive withstand current under a 10/350 μs waveform
Example:
- Iimp = 12.5 kA → Can withstand 15 instances of 12.5 kA 10/350 μs impulses
- Iimp = 25 kA → Can withstand 15 instances of 25 kA 10/350 μs impulses
- Iimp = 50 kA → Can withstand 15 instances of 50 kA 10/350 μs impulses
How to determine the required Iimp?
Step 1: Assess lightning activity density (Flash Density, FD)
International classification of lightning activity density:
FD < 1 flash/km²/year → Low-risk area
FD = 1-5 flash/km²/year → Moderate risk
FD = 5-10 flash/km²/year → Relatively high risk
FD > 10 flash/km²/year → High-risk area
FD > 20 flash/km²/year → Extremely high risk
Actual regional reference:
| Region | Risk Level | Recommended Iimp |
| Northern Europe | Low–Medium | 12.5 kA |
| Southern Europe | Medium | 12.5–25 kA |
| Northern United States | Medium | 12.5 kA |
| Southern United States (Florida) | High | 25 kA |
| Southern China | Relatively High | 12.5–25 kA |
| Central China | Medium–Relatively High | 12.5 kA |
| Southeast Asia (Tropical Regions) | Extremely High | 25–50 kA |
| Northern Australia | High | 25 kA |
| Central India | High | 25 kA |
| Brazil | High | 25–50 kA |
Step 2: Consider the building type and importance
Building importance classification:
Grade A: Extremely high importance (hospitals, data centers, chemical plants) → Iimp = 50kA or higher, requires redundant configuration
Grade B: High importance (commercial buildings, office buildings, schools) → Iimp = 25kA, standard configuration
Grade C: Medium importance (residential buildings, shops, restaurants) → Iimp = 12.5kA, economical configuration
Grade D: Low importance (warehouses, garages, temporary structures) → Iimp = 12.5kA (minimum standard)
Step 3: Consider architectural structural factors
Steel frame buildings:
- Possess certain lightning diversion capabilities (metal frames can disperse surges)
- Iimp can be set to standard values
Masonry/Wooden structure buildings:
- No metal structures to aid in surge diversion
- Entire surge relies on Type 1 SPD
- Iimp should be set to a higher value (+25%)
High-rise buildings (>30m):
- Direct lightning strike risk significantly increases
- If the roof has a lightning protection system, Iimp ≥ 25kA is required
- If the roof lacks a lightning protection system, Iimp ≥ 50kA is required
Rural/Isolated buildings:
- No tall surrounding objects to divert lightning strikes
- Increased risk of direct lightning strikes
- Iimp should be set to a higher value
Comprehensive Recommendation Table:
| Building Type | Lightning Activity (Region) | Recommended Iimp |
| Small residential | Medium | 12.5 kA |
| Small residential | High / Extremely high | 25 kA |
| Commercial building | Medium | 12.5–25 kA |
| Commercial building | High | 25 kA |
| Office building | Any | 25 kA |
| Hospital | Any | 50 kA + redundancy |
| Data center | Any | 50 kA + redundancy |
| Industrial facility | Medium | 25 kA |
| Industrial facility | High | 50 kA |
| Solar PV plant (DC side) | Any | 50 kA |
| EV charging station | Medium | 25 kA |
| EV charging station | High | 50 kA |
Nominal discharge current and maximum discharge current (In / Imax)
Although the core indicator of Type 1 SPD is Iimp, In and Imax are still important references.
In（Nominal Discharge Current）
In is the rated current that the SPD can repeatedly (≥15 times) withstand under an 8/20 μs waveform.
Typical In value of Type 1 SPD:
| Type 1 Iimp | Corresponding In (Typical) |
| 12.5 kA | 15–20 kA |
| 25 kA | 25–40 kA |
| 50 kA | 50–80 kA |
Imax（Maximum Discharge Current）
Imax is the maximum current that an SPD can withstand in a single instance (only once) under an 8/20 μs waveform.
Key differences:
- In = withstand multiple times (≥15 times)
- Imax = withstand a single time
- Imax > In, typically Imax ≈ 2-3 × In
Typical Imax value of Type 1 SPD:
| Type 1 Iimp | Corresponding Imax (Typical) |
| 12.5 kA | 30–50 kA |
| 25 kA | 50–100 kA |
| 50 kA | 100–200 kA |
Rated voltage (120V / 240V / 400V / 690V)
The rated voltage determines the type of power grid where Type 1 SPD can be installed.
Uc (Maximum Continuous Operating Voltage) is the maximum operating voltage that an SPD can continuously withstand; exceeding this voltage may damage the SPD.
Important principle: Uc must be ≥ the system’s maximum operating voltage.
Calculation of the system’s maximum operating voltage:
- Single-phase 220V system: Maximum operating voltage = 220V × 1.1 = 242V
- Three-phase 380V system: Maximum operating voltage = 380V × 1.1 = 418V
- Three-phase 400V system: Maximum operating voltage = 400V × 1.1 = 440V
- Three-phase 415V system: Maximum operating voltage = 415V × 1.1 = 457V
UC Recommendation
| System | Voltage | Recommended Uc |
| Single-phase | 230V | 275V (L-N) |
| Three-phase | 230V/400V | 275V (L-N) or 440–460V (L-L) |
Industrial application (690V three-phase)
| System | Voltage | Recommended Uc |
| High-power three-phase | 690V | 750–800V (L-L) |
Protection Level (Up)
Up is the ultimate performance indicator of SPD, determining whether downstream equipment can be effectively protected.
Up (Voltage Protection Level) is the maximum voltage that an SPD can maintain at both ends while diverting a surge.
Up（Voltage Protection Level）
Key understanding:
- The lower the Up, the better the protection for the equipment.
- Up is the “residual voltage” that equipment can withstand.
- The equipment’s voltage tolerance must be ≥ Up; otherwise, the equipment will be damaged.
The relationship between Up and device withstand voltage
The voltage withstand capability of typical equipment:
| Equipment Type | Withstand Voltage Capability |
| Household appliances | 4–6 kV |
| Lighting equipment | 2–4 kV |
| Office equipment (computers) | 1.5–2 kV |
| Industrial controllers (PLC) | 2–4 kV |
| Variable frequency drives (VFD) | 4–6 kV |
| Medical equipment | 1–3 kV |
| Servers / networking equipment | 1.5–2 kV |
| Sensitive electronic devices | 1–2 kV |
Key to Up selection:
Up < Device withstand voltage × Safety margin
Example: Protecting a server
- Server withstand voltage = 2kV
- Safety margin = 1.3 times
- Up must ≤ 1.5kV
Example: Protecting common household appliances
- Appliance withstand voltage = 4kV
- Safety margin = 1.3 times
- Up must ≤ 3kV
Typical Up of Type 1 SPD
According to the Iimp level, the Up range of Type 1 SPD:
| Iimp | Typical Up Range | Level |
| 12.5 kA | 1.5–2.5 kV | Excellent |
| 25 kA | 1.8–2.5 kV | Excellent |
| 50 kA | 2.0–3.0 kV | Good |
| 100 kA | 2.5–3.5 kV | Average |
Up recommendation table
| Application | Recommended Up |
| General buildings | 2.0–2.5 kV |
| Buildings with computers and servers | 1.5–2 kV |
| Data centers and medical facilities | < 1.5 kV |
| Industrial control systems | 2.0–2.5 kV |
Pole selection (1P / 2P / 3P / 4P)
The selection of pole numbers depends on the type of power grid and protection requirements.
The number of poles of SPD refers to the number of conductors that the SPD can protect simultaneously.
1 pole (1P): 1 conductor (usually L-PE protection)
2 poles (2P): 2 conductors (e.g., L1-N, N-PE)
3 poles (3P): 3 conductors (3 phase lines)
4 poles (4P): 4 conductors (3 phase lines + N line)
Pole selection for different power grids
Single-phase system:
1-phase 220V system:
- Polarity: 1P+N or 2P
- L (live wire) → Type 1 SPD → Main circuit breaker
- N (neutral wire) → Type 1 SPD → Neutral busbar
- PE → Equipotential bonding
Recommendation: 1P+N or 2P SPD
3-phase system:
3-phase 3-wire 380V system (no N wire required, such as industrial motors):
- Polarity: 3P
- Phase A, B, C pass through SPD
3-phase 4-wire 220V/380V system (most common):
- Polarity: 3P+N or 4P
- Phases A, B, C + N wire all pass through SPD
Recommendation: 3P+N SPD
Recommended Table of Polar Selection
| Application | Recommended Poles | Recommended Configuration |
| Single-phase residential | 1P+N or 2P | L–N dual-pole protection |
| Three-phase residential | 3P+N | Full three-phase + neutral protection |
| Small commercial | 3P+N or 1P+N | Depends on distribution system |
| Large commercial | 3P+N or 4P | Full system protection |
| Industrial (3-phase, 3-wire) | 3P | Three-phase only protection |
| Industrial (3-phase, 4-wire) | 3P+N or 4P | Full system protection |
| Hospital / Data center | 3P+N or 4P + redundancy | High-level protection |
Typical application scenarios of Type 1 surge protectors
Main power distribution system of commercial buildings
Commercial buildings have higher requirements for surge protection as it concerns business continuity and economic losses.
Type 1 SPD Application Locations in Commercial Buildings
Location 1: Main Switch Room (MSR)
- Incoming main switch for the entire building
- Typically located in the basement or ground floor distribution room
- Type 1 SPD installed at the incoming terminal of the main distribution panel
Location 2: Distribution Room on Each Floor
- Independent distribution rooms for each floor or area
- SPD installed at the incoming terminal of the distribution panel
Location 3: Front End of Critical Loads
- Data centers, network equipment rooms
- Fire control rooms
- Main elevators
Selection of Type 1 SPD for commercial buildings
| Parameter | Recommended Value | Description |
| Iimp | 25 kA (medium risk) / 50 kA (high risk) | 10/350 μs |
| Imax | 100–150 kA | 8/20 μs |
| Uc | 320 V (230/400 V system) / 440 V (277/480 V system) | Maximum continuous operating voltage |
| Up | ≤ 1.5 kV (critical loads) / ≤ 2 kV (general loads) | Protection level |
| Poles | 3P+N (standard) / 4P (critical loads) | Number of poles |
| IP rating | IP54 (outdoor) / IP30 (indoor) | Industrial protection rating |
Industrial power distribution system
The industrial environment is a high-risk area for Type 1 SPD applications because industrial equipment is extremely sensitive to surges, and the consequences are severe.
Lightning Protection Zones (LPZ) in Industrial Power Distribution Systems
LPZ 0A: Direct lightning strike zone
- Exposed equipment outside the plant (e.g., storage tanks, chimneys)
- Requires Type 1 SPD direct protection
LPZ 0B: Indirect lightning strike zone
- Open areas inside the plant premises
- Requires Type 1 SPD protection for incoming lines
LPZ 1: Inside buildings
- Indoor spaces within workshops
- Requires Type 2 SPD protection for distribution panels
LPZ 2: Inside control rooms
- PLC/DCS control cabinet interiors
- Requires cascading protection with Type 2 + Type 3 SPDs
LPZ 3: Port circuits
- Instrument/sensor interfaces
- Requires dedicated signal line SPD protection
Type 1 SPD Applications in Industrial Systems
- Main Switch Room: Iimp ≥ 25kA
- Shop Floor Level 1 Distribution: Iimp ≥ 12.5kA
- Outdoor Switchboard: Iimp ≥ 25kA
- Critical Load Front End: Iimp ≥ 25kA, can be combined with Type 2
Selection of Type 1 SPD for Industrial Systems
| Parameter | Recommended Value | Description |
| Iimp | ≥ 25 kA (indoor) / ≥ 50 kA (outdoor) | 10/350 μs |
| Imax | ≥ 100 kA | 8/20 μs |
| Uc | ≥ 440 V (380 V system) / ≥ 600 V (480 V system) | Maximum continuous operating voltage |
| Up | ≤ 2 kV (general loads) / ≤ 1.5 kV (critical loads) | Protection level |
| Poles | 3P+N (three-phase, four-wire) / 3P (three-phase, three-wire) | Number of poles |
| IP rating | IP54 (outdoor) / IP30 (indoor) | Industrial protection rating |
| Temperature | -40°C to +70°C | Industrial operating temperature range |
Why Choose LSP for Type 1 SPDs
At LSP, we have been dedicated to the research and production of surge protection devices (SPDs) since 2010, with a strong focus on delivering reliable Type 1 SPDs to global markets. With over a decade of experience, our products are now exported to more than 10 countries, supported by two automated production lines and a 1600㎡ facility certified with ISO9001, TUV, CB, and CE. We ensure production efficiency with a standard delivery time of 10–15 days for regular models and one month for custom orders. Even in cases with no inventory, we maintain a maximum lead time of two months.
What sets our Type 1 SPDs apart is our commitment to high-performance components and rigorous testing. We use top-tier materials like LKD MOVs and Vactech GDTs, both trusted by global SPD leaders. Our metal parts undergo a 48-hour salt spray test and feature thicker terminals (8mm x 0.8mm) for enhanced durability. Our SPDs are designed with an internal disconnector that has been developed over three years, ensuring safe isolation and arc suppression during surges. With dual testing certifications (8/20 and 10/350 waveforms), low-temperature tripping technology, and added moisture protection, our Type 1 SPDs offer unmatched safety and lifespan of over five years.
We also provide customized solutions to meet specific market needs. Our in-house R&D team supports design customization, 3D modeling for marketing, and assistance with obtaining secondary certifications like TUV, CB, and CE. From pre-sales technical consultation to efficient logistics and global after-sales support, including a 5-year warranty and fast response times, we aim to deliver not just high-quality products but a complete, reliable service experience.
FAQ
Can Type 1 SPD replace Type 2 SPD?
No. Type 1 SPD is designed for high-energy lightning surge protection at the service entrance, while Type 2 SPD protects against residual surges in distribution boards. Type 1 cannot replace Type 2 because they serve different protection levels in a coordinated system.
What is the best position to install an SPD in the main distribution panel?
The SPD in the main distribution panel should be installed after the main incoming breaker and as close as possible to the power entry point, with a very short grounding connection to the PE terminal to reduce impedance and ensure effective surge diversion to downstream circuits.
What is the lifespan of a Type 1 SPD?
The lifespan of a Type 1 SPD is typically 5–10 years, depending on surge frequency, lightning intensity, and operating conditions. In high lightning areas or frequent surge events, the lifespan may be significantly shorter and requires regular inspection.
Can Type 1 SPD protect against direct lightning strikes?
Type 1 SPD can withstand and partially divert direct or nearby lightning surges (10/350 μs) by discharging most of the energy to ground, but it cannot completely stop lightning itself; it only reduces its destructive impact on the system.
