逆流して上昇：安全靴の耐圧テストの技術的視点

In professions where accidental contact with live electrical circuits poses a significant hazard, specialized safety footwear with electrical insulating properties is paramount. To ensure the wearer's protection, these shoes undergo rigorous voltage resistance testing, also known as dielectric strength testing. This technical article explores the principles, procedures, and critical importance of this electrical safety assessment for footwear.

The Core Principle: Electrical Insulation

The fundamental principle behind voltage resistance testing of safety footwear is to evaluate its ability to act as an electrical insulator, preventing the flow of dangerous current through the wearer's body to the ground. The test simulates accidental contact with a live electrical source at a specific voltage. The footwear must withstand this voltage for a defined period without experiencing electrical breakdown or allowing excessive leakage current.

The Testing Setup and Procedure:

Standard voltage resistance testing for safety footwear typically involves the following key elements and procedures, often guided by standards such as ASTM F2413 and EN ISO 20344 (which references dielectric requirements):

Electrodes: The test utilizes two electrodes to apply the test voltage across the footwear. One electrode is typically placed inside the shoe, often by filling it with a conductive medium like water or using conductive metal spheres. The other electrode is placed on the outer sole of the shoe, often a conductive plate or a water bath in which the shoe is partially submerged.

Voltage Application: A high-voltage power supply with a controlled output is connected to the electrodes. The test voltage, which can range from several thousand to tens of thousands of volts depending on the safety class of the footwear and the relevant standard, is gradually increased to the specified level at a controlled rate.

Test Duration: Once the specified test voltage is reached, it is maintained for a defined period, typically one minute.

Leakage Current Measurement: During the test, the current flowing through the footwear (leakage current) is precisely measured. The relevant safety standards specify maximum allowable leakage current values. If the leakage current exceeds this limit, the footwear fails the test.

Dielectric Breakdown Assessment: After the test duration, the footwear is inspected for any signs of dielectric breakdown, such as puncture, tracking (formation of conductive paths on the surface), or flashover (electrical discharge over the surface of the insulation). Any breakdown constitutes a failure.

Why is Voltage Resistance Testing Crucial?

Voltage resistance testing is an indispensable element in ensuring the safety of electrically insulating footwear. It provides objective evidence of the shoe's ability to protect wearers from electrical shock hazards in environments where they might encounter live circuits. Passing this test, according to recognized safety standards, signifies that the footwear offers a defined level of electrical insulation, minimizing the risk of potentially fatal electrical injuries. This testing is particularly critical for professionals working in:

Electrical power generation and distribution

Telecommunications

Maintenance and repair of electrical equipment

Construction and industrial settings with potential electrical hazards

Connecting to Standards:

Standards like ASTM F2413 in North America and EN ISO 20344 in Europe (which incorporates requirements from standards like EN 50321-1 for electrically insulating footwear) outline specific voltage resistance test procedures and performance requirements for different classes of safety footwear designed for electrical hazard protection. These standards specify the test voltages, maximum leakage currents, and acceptable post-test conditions. While IEC 60903 primarily focuses on electrical insulating gloves, its principles of dielectric testing are relevant to understanding the requirements for insulating footwear.

Conclusion:

Voltage resistance testing of safety footwear is a critical technical evaluation that verifies its electrical insulating properties. By subjecting the footwear to high voltages under controlled conditions and measuring the resulting leakage current and assessing for dielectric breakdown, this testing provides essential assurance that the footwear can effectively protect individuals from electrical shock hazards in their work environments. Adherence to stringent international standards and thorough voltage resistance testing are paramount in ensuring the safety and well-being of workers in electrically hazardous occupations.