Power systems today face increasing exposure to lightning strikes, switching transients, and grid disturbances. Whether in industrial plants, photovoltaic systems, telecommunications infrastructure, or data centers, Surge Protective Devices (SPDs) play a critical role in preventing expensive equipment damage.
When selecting an SPD, many users focus on discharge current capacity and voltage protection level. However, one important parameter is often overlooked:
Leakage current.
Many engineers ask:
Is lower leakage current always better?
Can an SPD achieve zero leakage current?
How does leakage current affect reliability and lifespan?
This article explains the technical principles behind SPD leakage current and helps you choose the right surge protection solution for long-term system reliability.
What Is SPD Leakage Current?
SPD leakage current refers to the small amount of current that continuously flows through the surge protection element during normal operating conditions.
For conventional MOV (Metal Oxide Varistor)-based surge protectors, a small current naturally exists because MOV materials are voltage-dependent resistive components.
Under normal conditions:
Typical leakage current values are measured in microamps.
Industry reference:
Static leakage current:
I ≤ 20 μA
This current generally does not damage the protected equipment or system.
However, the real concern is not the existence of leakage current itself.
The issue is whether the leakage current remains stable over time.
Why Leakage Current Matters in Real Applications
At first glance, leakage current seems insignificant.
But over time, continuous current flow can generate heat inside the SPD.
The process often develops as follows:
Leakage Current Increase
↓
Internal Temperature Rise
↓
MOV Material Aging
↓
Protection Performance Degradation
↓
Thermal Runaway
↓
Potential Fire or Explosion Risk
This is why leakage current stability directly affects:
✔ Product lifespan
✔ Thermal performance
✔ Safety
✔ Maintenance costs
✔ Long-term reliability
Is Smaller Leakage Current Always Better?
The simple answer:
Not always.
Many users only compare the initial leakage current values listed in product specifications.
However, practical reliability depends more on long-term stability.
Let's compare two common scenarios.
Low Initial Leakage Current Design
Initial leakage current:
3–6 μA
Advantages:
Low initial power consumption
Low heat generation
Potential disadvantages:
Leakage current may gradually increase over time
Internal aging may accelerate
Thermal stress may increase
Stable Leakage Current Design
Initial leakage current:
20–30 μA
Advantages:
Better long-term stability
Predictable performance
Lower risk of sudden degradation
Improved reliability
Technical Comparison
| Parameter | Ultra-Low Initial Leakage | Stable Leakage Design |
|---|---|---|
| Initial current | Lower | Slightly higher |
| Long-term stability | Medium | High |
| Thermal stability | Moderate | Excellent |
| Aging resistance | Lower | Higher |
| Service life | Shorter | Longer |
| Industrial suitability | Moderate | Excellent |
The key takeaway:
Stable leakage current is often more important than the smallest possible leakage current value.
Can a 0-Leakage SPD Exist?
Traditional MOV-based SPDs cannot achieve absolute zero leakage current.
This is due to the physical characteristics of MOV materials.
However, newer technologies can significantly reduce leakage current.
How Composite SPD Technology Reduces Leakage Current
Modern SPD designs increasingly use composite protection structures, combining technologies such as:
MOV elements
Isolation structures
Gap discharge technology
Series protection mechanisms
Advantages include:
✔ Near-zero leakage current
✔ Near-zero follow current
✔ Reduced self-heating
✔ Longer operating life
✔ Better thermal performance
✔ Lower fire risk
Compared with conventional MOV-only designs, composite SPDs greatly improve reliability in demanding environments.
Why Low Leakage Current Matters for Solar and Industrial Systems
Some applications place continuous stress on surge protection devices.
Solar PV Systems
Challenges include:
Continuous DC voltage exposure
Elevated temperatures
Long operating cycles
Wind Energy Systems
Challenges include:
Frequent lightning exposure
Harsh environmental conditions
Limited maintenance accessibility
Industrial Facilities
Challenges include:
High electrical noise
Heavy equipment switching
Continuous operation requirements
For these applications, long-term leakage current stability becomes critical.
How to Select the Right SPD
Residential Buildings
Recommended:
Standard MOV surge protectors
Suitable for basic protection requirements.
Industrial Systems
Recommended:
Stable low-leakage designs
Suitable for long operating periods.
Solar PV Systems
Recommended:
DC-specific SPD
High TOV capability
Enhanced thermal performance
Wind Power Applications
Recommended:
Composite SPD technology
Long-life design
High reliability architecture
Why Choose ONCCY Surge Protection Solutions?
ONCCY is a professional electronic component manufacturer specializing in complete surge protection technologies.
ONCCY provides:
✔ Type 1 Surge Protective Devices
✔ Type 2 Surge Protective Devices
✔ Type 3 Surge Protective Devices
✔ Signal Surge Protectors
✔ DC Surge Protectors
✔ Wind Power SPD Solutions
✔ 1500+ product specifications
✔ UL / CE / TUV / CSA / CQC certified products
ONCCY Advantages
High surge discharge capability
Excellent thermal stability
Low residual voltage
High TOV withstand capability
Long operating lifespan
Compact design
Industrial-grade reliability
Applications include:
Power systems
Renewable energy
Telecommunications
Rail transportation
Petrochemical industries
Smart buildings
Frequently Asked Questions
Does lower leakage current always mean a better SPD?
Not necessarily. Long-term stability is often more important than extremely low initial values.
Can traditional MOV SPDs have zero leakage current?
No. Conventional MOV technology naturally produces small leakage currents.
Why does leakage current increase over time?
Factors include:
Aging
Repeated surge exposure
Thermal stress
Material degradation
Why should leakage current be tested regularly?
Leakage current testing helps identify deterioration and prevent unexpected failures.
Which applications benefit most from low leakage SPDs?
Solar systems, wind systems, industrial facilities, and critical power infrastructure benefit significantly.
Contact ONCCY
Choosing an SPD is not only about surge capacity.
Long-term reliability, thermal performance, and leakage current stability directly impact system safety and operational costs.
Contact ONCCY today to find the right surge protection solution for your application.