In the field of electrical equipment safety testing, the creepage distance test card is a tool that seems unremarkable but is crucial. It can quickly determine whether the creepage distance between the insulating components of equipment meets standards, thereby preventing electric leakage, short circuits, and even fire accidents caused by insufficient insulation gaps. However, most people may not know that the size of the test card is by no means a "one-size-fits-all" specification. Instead, it is "customized" based on the core requirements of electrical safety, and every 1mm of design is directly linked to the safety bottom line of the equipment.

What is Creepage Distance? Why Does Test Card Size Matter?

Creepage distance refers to the shortest distance between two live parts, or between a live part and a grounded part in electrical equipment, along the surface of insulating materials (distinguished from "clearance"—the shortest distance through the air). When the equipment is energized, current may "creep" along the surface of the insulation to form leakage current; if the creepage distance is insufficient, it can easily cause insulation breakdown, leading to safety accidents.

The creepage distance test card is essentially a "standard distance template". By comparing it with the actual creepage path of the equipment, it can quickly determine whether the equipment meets safety standards. Therefore, the core of test card size design lies in "precisely matching safety standards and test scenarios"—it should neither be arbitrarily reduced nor blindly enlarged.

Core Factors Determining Test Card Size

1.Primary Basis: Authoritative Electrical Safety Standards

All test card sizes are based on international, national, or industry standards, which directly determine their core dimensions:

International Standards (e.g., IEC 60664, IEC 61140): These specify minimum creepage distances for different voltage levels and pollution degrees. For example, in a 250V AC environment with pollution degree 2, ordinary insulation requires a minimum creepage distance of ≥3mm – so the test card must include a 3mm scale.

National Standards (e.g., GB/T 16935.1, GB 4706.1): These align with international standards while adding industry-specific details. For instance, kitchen appliances operate in humid conditions (pollution degree 3), so their creepage distance under 220V needs to increase from 3mm to 3.6mm – and the test card size adjusts accordingly.

Industry-Specific Standards (e.g., ISO 6469 for automotive electrical systems): These address the challenges of strong vibration and large temperature fluctuations in vehicles. Test cards must match the needs of 48V high-voltage systems and narrow PCB component gaps, with minimum scales as precise as 0.5mm.

In short, test cards must accurately reflect the millimeter requirements set by standards – this forms an uncrossable safety threshold.

2. Key Adaptation: Test Scenario Characteristics

Even for the same 3mm creepage distance requirement, test card sizes may differ between household sockets and industrial inverters, as they must adapt to specific scenarios:

Equipment Structure: For small devices (e.g., mobile phone chargers, headphone motherboards), we use thin and narrow cards (thickness ≤1mm, width ≤5mm) to easily access dense components. For large equipment (e.g., power distribution cabinets, motor controllers), we extend the grip length (10-15cm) to facilitate accurate alignment and prevent electric shock.

Gap Shape: For linear gaps (e.g., two parallel electrodes), we use straight strip cards to directly compare linear distances. For curved gaps (e.g., cylindrical insulators), we add arc-shaped probes that fit the curve's curvature – ensuring we measure the "shortest path along the curve" rather than a straight line.

Operating Environment: For laboratory testing, we can use slightly larger cards (10-20cm in length) for easy reading. For on-site maintenance (e.g., outdoor power distribution boxes), we use portable foldable cards – these meet standard sizes when unfolded and fit into tool bags when folded, balancing practicality and precision.

3. Hidden Guarantee: Material and Precision (Dimensional Stability)

Test card sizes require both "accurate design and long-term stability", so we must consider material properties to compensate for potential errors.

Thermal Expansion and Contraction: For high-temperature environments, we use low-expansion materials (e.g., stainless steel). We also reserve negative tolerances during design (e.g., a standard 3mm size is designed as 2.995mm) to prevent misjudgment caused by thermal expansion.

Mechanical Strength and Deformation: If a test card exceeds 30cm in length, its own weight may cause bending and affect measurement accuracy. Thus, we add reinforcing ribs (e.g., increasing thickness from 1mm to 2mm) or use composite materials (e.g., plastic + glass fiber) for long cards to ensure dimensional stability.

Scale Clarity: For small scales (0.5-2mm), we use laser engraving (line width ≤0.1mm) to avoid reading errors from blurred scales. For large scales (10-50mm), we add numerical labels to enable quick identification.

Conclusion: The Rigorous Logic of "Safety First" Behind Sizes

Creepage distance test card sizes never come from "random decisions" – they result from the integration of standards, scenario characteristics, material precision, and user needs. Every millimeter of design aims at the core goal of "accurate testing and safety assurance".

When selecting test cards, enterprises and inspectors must not only focus on size values but also verify compliance with relevant standards and suitability for the test object. Only precisely matched sizes can make creepage distance testing truly effective and build a solid defense for the safe operation of electrical equipment.

PEGO has launched a variety of creepage distance test cards in different sizes, tailored to meet various electrical safety standards. Each test card set includes both straight-type and curved-type probes, all made of stainless steel, with clear and legible scales—ensuring accurate adaptation to creepage distance testing needs in different scenarios. Should you be interested in this product, please feel free to contact us.