Not sure whether to choose a 20kA, 40kA, 65kA, or 80kA surge protective device?
Many SPD buyers compare products by the kA number first. A higher Imax rating looks stronger. It also usually costs more. But Imax should not be selected by the idea of “the bigger, the better.”
The right Imax depends on the installation position, lightning exposure, system importance, SPD type, project specification, and budget.
This guide explains how to choose SPD Imax for distribution boards, industrial panels, high-lightning areas, and bulk OEM orders.
Índice
Quick Answer: Which SPD Imax Should You Choose?
For most standard distribution boards, 40kA is the most common Type 2 SPD choice.
For smaller panels or cost-sensitive OEM orders, 20kA may be enough if the installation risk is low.
For industrial panels, exposed buildings, unstable grids, or higher project requirements, 65kA gives more surge-current margin.
For high-lightning areas, main incoming panels, and critical equipment, 80kA may be selected when the project needs a higher protection level.
| SPD Imax | Common Use | Buyer Meaning |
|---|---|---|
| 20kA | Small distribution boards, indoor sub-panels, low-risk areas | Cost-effective option for light-duty applications. |
| 40kA | Standard distribution boards, commercial panels, most OEM cabinets | Most common balance between protection capacity and price. |
| 65kA | Industrial panels, exposed buildings, unstable grids, higher project specs | Higher surge-current margin than standard 40kA SPDs. |
| 80kA | Main incoming panels, high-lightning areas, critical equipment | High-capacity option for demanding projects. |
Regra simples:
Choose 20kA for low-risk panels. Choose 40kA for standard distribution boards. Choose 65kA for industrial or higher-risk systems. Choose 80kA when the installation is exposed, critical, or clearly specified by the project.
Need help choosing the right SPD Imax?
Send us your panel type, system voltage, SPD type, and target quantity. Our team can recommend a suitable model for OEM or distribution board orders.
What Does Imax Mean on an SPD?
Imax means corrente máxima de descarga.
It is the maximum peak value of an 8/20 μs surge current that the SPD can discharge under specified test conditions.
In simple words, Imax shows the SPD’s maximum surge-current capacity in a severe surge event.
It is an important rating, especially for Type 2 SPDs. But Imax is not the same as normal working current. It also does not tell you everything about the SPD’s life, protection level, or suitability for your system.
A 40kA SPD is not “working at 40kA every day.” It means the product has been tested for that maximum surge-current level under the relevant test conditions.
Imax Is Important, But It Should Not Be Read Alone
Many buyers ask suppliers only one question:
“Do you have 40kA SPD?”
This is a common way to start an inquiry. But it is not enough for final selection.
Before choosing Imax, you also need to check:
| Parâmetro | What It Means | Por que Isso Importa |
|---|---|---|
| Tipo de DPS | Type 1, Type 2, or Type 1+2 | Different installation positions need different SPD types. |
| Uc | Tensão máxima de funcionamento contínuo | Must match the real system voltage. |
| Em | Corrente de descarga nominal | Shows repeated surge-duty capability. |
| Imax | Corrente máxima de descarga | Shows maximum 8/20 μs surge-current capacity. |
| Para cima | Nível de proteção da tensão | Shows how much residual voltage may reach the equipment. |
| Iimp | Impulse current for Type 1 SPD | Important for direct lightning current applications. |
| Postes | 1P, 2P, 3P, 4P, 3P+N | Must match the power system and wiring method. |
A high Imax with the wrong Uc is still the wrong SPD.
A high Imax with poor installation wiring may not protect the equipment well.
A high Imax Type 2 SPD cannot automatically replace a Type 1 SPD when the project requires direct lightning current protection.
The real question is not “Which Imax is the biggest?” The real question is “Which Imax is suitable for this installation point and risk level?”
20kA SPD: When Is It Enough?
A 20kA SPD is usually selected for lighter-duty protection.
It may be suitable for small distribution boards, indoor sub-panels, low-exposure buildings, or cost-sensitive OEM electrical panels.
Typical applications include:
- Small residential or commercial distribution boxes
- Indoor sub-distribution boards
- Low-risk electrical panels
- Basic OEM electrical cabinets
- Projects where the specification does not require higher Imax
- Budget-sensitive bulk orders
For these applications, a 20kA SPD can be a practical choice when the system is not highly exposed to lightning or severe switching surges.
However, 20kA should not be used blindly.
It may not be the best choice for:
- Painéis principais de entrada
- Outdoor distribution boxes
- Industrial facilities
- Areas with frequent thunderstorms
- Long overhead line exposure
- Critical equipment protection
- Projects where the consultant specifies 40kA or higher
If the buyer only wants the lowest price, 20kA may look attractive. But if the panel is exposed or the maintenance cost is high, the lower purchase cost may not be the best decision.
40kA SPD: The Most Common Choice for Standard Distribution Boards
A 40kA SPD is one of the most common choices for Type 2 surge protection.
For many standard distribution boards, it gives a good balance between protection capacity, product size, availability, and price.
Typical applications include:
- Standard AC distribution boards
- Commercial building panels
- OEM electrical cabinets
- Three-phase distribution boxes
- Sub-main distribution boards
- General industrial control panels
- Electrical panels for distributors and stock orders
This is why many buyers ask for 40kA first.
For normal B2B procurement, 40kA is often the safest starting point. It is not the cheapest option, but it is widely accepted in many standard projects.
For OEM buyers, 40kA is also easier to explain to end users. It looks more reliable than 20kA and is often easier to sell as a standard protection level.
For standard Type 2 AC distribution board applications, you can also review our LY1-C40/4(S) Type 2 AC SPD with 20kA In and 40kA Imax . This model is commonly used for low-voltage AC distribution systems, power cabinets, commercial electrical installations, and OEM panel applications.
65kA SPD: When a Higher Surge Margin Is Needed
A 65kA SPD is usually selected when the project needs more surge-current capacity than standard 40kA models.
It is not only a “bigger number.” It is often used when the buyer wants a stronger product for more demanding environments.
Typical applications include:
- Quadros de distribuição industrial
- Factories with heavy electrical loads
- Buildings in areas with higher lightning activity
- Outdoor or semi-outdoor electrical cabinets
- Unstable grids
- Painéis de controle de bombas
- Machinery control cabinets
- Projects with stricter electrical specifications
- Distributors who want a higher-grade SPD stock option
A 65kA SPD is useful when the customer wants more margin but does not necessarily need the highest 80kA option.
In many industrial projects, the cost difference between 40kA and 65kA is smaller than the cost of equipment damage, maintenance visits, or production interruption.
For larger distribution boards, industrial panels, and higher-risk electrical rooms, you can also review our SPD for distribution board selection guide . It explains how Type 2 and Type 1+2 DIN rail SPDs are selected for main boards, sub-distribution boards, consumer units, and industrial electrical panels.
80kA SPD: For High-Risk or Specification-Driven Projects
An 80kA SPD is a high-capacity Type 2 option.
It is usually selected for more demanding applications, especially when the installation has higher surge exposure or when the project specification clearly requires it.
Typical applications include:
- Main incoming distribution panels
- High-lightning areas
- Exposed buildings
- Outdoor power distribution
- Critical equipment protection
- Industrial main panels
- Telecom or infrastructure power systems
- Premium OEM panels
- Projects where consultants specify 80kA
An 80kA SPD may be a good choice when the buyer wants stronger surge-current capacity and is willing to pay for a higher specification.
If the building has an external lightning protection system, or if the installation point may be exposed to direct lightning current, Type 2 Imax alone may not be enough. The project may need a Type 1 or Type 1+2 SPD with a suitable Iimp rating.
For high-risk incoming boards, exposed buildings, or main distribution panels, see our Type 2 and Type 1+2 SPD selection guide for distribution boards .
20kA vs 40kA vs 65kA vs 80kA: Practical Selection Table
Imax should be selected according to where the SPD is installed. The SPD at the main incoming panel usually faces a higher surge risk than a small downstream sub-panel.
| Aplicação | Common Imax Choice | Razão | Related Page |
|---|---|---|---|
| Indoor distribution box | 20kA or 40kA | Low exposure, limited budget, basic protection. | 40kA Type 2 AC SPD |
| Commercial distribution board | 40kA | Common balance between cost and protection. | LY1-C40 Type 2 SPD |
| General OEM panel | 40kA | Easy to stock, easy to sell, widely accepted. | 40kA OEM SPD option |
| Armário de controle industrial | 40kA or 65kA | Higher equipment value and higher surge exposure. | Distribution board SPD selection |
| Main distribution panel | 65kA or 80kA | More important installation point, higher risk. | Type 2 / Type 1+2 SPD guide |
| Outdoor electrical cabinet | 65kA or 80kA | More exposure to lightning and switching surges. | Incoming board SPD selection |
| High-lightning installation | 65kA or 80kA | Higher surge-current margin is usually preferred. | Higher-risk SPD selection |
| Critical equipment supply | 65kA or 80kA | Failure cost is high, so stronger margin is useful. | Distribution board protection guide |
| External lightning protection project | Check Type 1 or Type 1+2 SPD | Iimp may be required, not only Imax. | Type 1+2 SPD selection |
This table is a selection guide, not a replacement for project design.
Final selection should also consider local standards, system voltage, earthing system, installation position, upstream protection, cable length, and project specifications.
Is a Higher Imax Always Better?
Não.
A higher Imax can provide a higher surge-current margin. But it is not always the best choice for every project.
A larger Imax may also mean:
- Higher product cost
- Larger internal MOV capacity
- Different product structure
- Higher stock cost for distributors
- Unnecessary over-specification for low-risk panels
For example, using an 80kA SPD in a small indoor sub-panel may not bring meaningful practical value if the system risk is low and the project only needs standard protection.
At the same time, using a 20kA SPD in a high-risk outdoor main panel may be under-specified.
The best SPD is not always the one with the largest Imax. The best SPD is the one that matches the real installation risk, project requirement, and budget.
Imax vs In: What Is the Difference?
Imax and In are both surge-current ratings, but they do different jobs.
Imax is the maximum discharge current. It shows the highest 8/20 μs surge-current capacity under specified test conditions.
In is the nominal discharge current. It is more related to repeated surge-duty capability under standard test conditions.
| Rating | Simple Meaning | Buyer Meaning |
|---|---|---|
| Em | Repeated surge-duty rating | Helps judge normal surge durability. |
| Imax | Maximum surge-current rating | Helps judge upper surge-current capacity. |
If two SPDs both have 40kA Imax, the one with a higher In rating may offer stronger repeated surge-duty performance, if all other conditions are similar.
That is why professional buyers should not compare Imax alone. When reviewing a datasheet, check both In and Imax.
Imax vs Iimp: Do Not Confuse Type 2 and Type 1 Ratings
Imax is commonly used for Type 2 SPDs and is based on the 8/20 μs surge-current waveform.
Iimp is used for Type 1 SPDs and is related to the 10/350 μs impulse current waveform.
This difference matters because Type 1 and Type 2 SPDs are used for different protection positions.
| Rating | Usually Used For | Forma de onda | Main Meaning |
|---|---|---|---|
| Imax | DUP tipo 2 | 8/20 μs | Maximum discharge current for induced surge protection. |
| Iimp | DUP tipo 1 | 10/350 μs | Lightning impulse current capacity for direct lightning current risk. |
If your project requires Type 1 protection, do not only ask for a high Imax value. Ask for the correct Iimp rating.
For example, a Type 1+2 SPD may be required at the main incoming panel of a building with external lightning protection. A high-Imax Type 2 SPD alone may not satisfy that requirement.
Why Do 20kA, 40kA, 65kA, and 80kA SPDs Have Different Prices?
The price difference is not only about the printed kA number.
Different Imax ratings may involve different internal design and material costs.
Common cost factors include:
- MOV chip size
- MOV quantity
- Thermal disconnection structure
- Internal copper or conductive parts
- Module size
- Material da caixa
- Configuração de polos
- Remote signal contact
- Indicator design
- Certification and testing cost
- Production batch size
- OEM label and packaging requirements
A 4P 40kA SPD is not priced the same as a 1P 40kA SPD.
A 40kA SPD with remote signal contact may cost more than a basic 40kA SPD without remote signaling.
A certified model may also cost more than a non-certified low-cost model.
For bulk procurement, buyers should not compare price by Imax only. A correct comparison should include SPD type, Uc, In, Imax, Up, poles, remote signal contact, certificate, packing method, OEM label requirement, quantity, and delivery schedule.
Common Mistakes When Choosing SPD Imax
Mistake 1: Choosing the biggest Imax without checking the system
A higher Imax does not fix the wrong voltage rating, wrong SPD type, or poor installation. Always check Uc, Up, In, system type, and installation position.
Mistake 2: Using Type 2 Imax instead of Type 1 Iimp
If the installation needs Type 1 protection, check Iimp. Do not replace Type 1 requirements with a high-Imax Type 2 SPD.
Mistake 3: Comparing prices without matching pole configuration
A 1P SPD and a 4P SPD are not the same product. Always compare the same pole configuration.
Mistake 4: Ignoring the installation position
The SPD at the main incoming panel may need a higher rating than the SPD in a small sub-panel.
Mistake 5: Ignoring local lightning risk
A standard 40kA SPD may be enough for many panels, but high-lightning regions may need a higher rating or a different protection architecture.
Mistake 6: Ignoring In
Imax shows maximum surge capacity. In helps show repeated surge-duty capability. A complete selection should consider both.
How to Choose SPD Imax Step by Step
Step 1: Confirm the SPD type
First, decide whether the project needs Type 1, Type 2, or Type 1+2 SPD. If the project requires Type 1, check Iimp. If it is a standard downstream distribution panel, Type 2 SPD is commonly used.
Step 2: Confirm the installation position
Main incoming panels usually need stronger protection than small sub-panels. Outdoor or exposed panels also need more attention.
Step 3: Confirm the system voltage and Uc
The SPD must match the real system voltage. Do not choose Imax before confirming Uc.
Step 4: Estimate the surge exposure
Consider lightning frequency, overhead lines, outdoor installation, nearby industrial equipment, and grid stability. Higher exposure usually means higher Imax or a stronger protection design.
Step 5: Check the project specification
If the consultant, contractor, or tender document requires 40kA, 65kA, or 80kA, follow the project requirement. Do not downgrade the Imax only to reduce price.
Step 6: Compare In, Up, poles, and certificates
Do not compare Imax alone. A complete SPD comparison should include all major parameters.
Step 7: Confirm OEM and bulk order details
For distributors and panel builders, confirm label, packaging, quantity, datasheet, certificate, and delivery time before placing a bulk order.
Before Bulk Ordering SPDs, Confirm These Details
Before you ask for a quotation, prepare the following information. This will help the supplier recommend the correct model faster.
- AC or DC application
- Tensão do sistema
- Classificação Uc
- SPD type: Type 1, Type 2, or Type 1+2
- Required Imax: 20kA, 40kA, 65kA, 80kA, or project-specific
- Classificação In
- Required Up value
- Pole configuration: 1P, 2P, 3P, 4P, or 3P+N
- Earthing system: TN-S, TN-C-S, TT, or IT
- Installation position: main panel, sub-panel, control cabinet, or outdoor box
- Remote signal contact requirement
- Backup fuse or circuit breaker requirement
- Required standard or certificate
- OEM label or private label requirement
- Packaging method
- Target quantity
- Destination market
If you are not sure about the Imax rating, send the panel information to the supplier and ask for a model recommendation.
Example Inquiry Message for Buyers
We need Type 2 AC SPDs for distribution board assembly.
System voltage: 230/400V AC.
Application: commercial distribution panels.
Required Imax: 40kA or 65kA for comparison.
Poles: 4P.
Uc: please recommend.
Remote signal: optional.
Quantity: 500 pcs.
Please send datasheet, certificate information, price, MOQ, and delivery time.
This kind of inquiry is much easier for the supplier to answer than simply asking:
“How much is 40kA SPD?”
FAQ
40kA Imax é suficiente para um quadro de distribuição padrão?
Em muitos quadros de distribuição padrão, o SPD Tipo 2 de 40kA é uma escolha comum. Ele oferece um equilíbrio prático entre capacidade de proteção e preço. No entanto, a seleção final também deve considerar a tensão do sistema, a posição de instalação, a exposição a raios, o tipo de SPD, In, Up e os requisitos do projeto.
Quando devo escolher SPD de 65kA em vez de 40kA?
Escolha 65kA quando a instalação precisar de mais margem de corrente de surto do que um SPD padrão de 40kA. Isso pode se aplicar a painéis industriais, edifícios expostos, redes instáveis, áreas de alta incidência de raios ou projetos com especificações mais rigorosas.
Um SPD de 80kA é sempre melhor do que um SPD de 40kA?
No. An 80kA SPD offers higher surge-current capacity, but it may be unnecessary for low-risk indoor panels. It is better for high-risk, exposed, critical, or specification-driven projects.
Can I use a 20kA SPD for an industrial panel?
It depends on the project risk and specification. For many industrial panels, 40kA or 65kA is more common because equipment value and downtime cost are higher. A 20kA SPD may be too limited for exposed or important industrial installations.
What is the difference between Imax and In?
Imax is the maximum discharge current rating. It shows the SPD’s upper 8/20 μs surge-current capacity. In is the nominal discharge current rating. It is more related to repeated surge-duty capability. Both should be checked when selecting an SPD.
What is the difference between Imax and Iimp?
Imax is commonly used for Type 2 SPDs and is related to the 8/20 μs waveform. Iimp is used for Type 1 SPDs and is related to the 10/350 μs waveform. If the project requires Type 1 protection, check Iimp instead of only looking at Imax.
Why do different suppliers quote different prices for the same 40kA SPD?
Because the Imax number alone does not define the whole product. Price can change based on Uc, In, Up, pole configuration, remote signal contact, MOV design, certificate, housing material, OEM packaging, and order quantity.
What Imax should I choose for OEM electrical panels?
For general OEM electrical panels, 40kA is often a practical starting point. For cost-sensitive, low-risk panels, 20kA may be considered. For industrial or higher-specification OEM panels, 65kA or 80kA may be more suitable.
Need Help Choosing the Right SPD Imax?
LEEYEE supplies surge protective devices for distribution boards, industrial panels, solar PV systems, telecom equipment, and OEM applications.
If you are not sure whether to choose 20kA, 40kA, 65kA, or 80kA, send us your system voltage, panel type, installation position, and quantity.
Our team can recommend a suitable SPD model for your project or bulk order.
