Issues related to wires that need to be paid attention to during the inspection of electrical appliances

September 9, 2025

Wires, as the "lifeblood" of electrical appliances, their quality directly affects the safety and performance reliability of the products. During the inspection of electrical appliances, the inspection of wires is often overlooked, but it is a crucial part of quality control. For purchasers, brand owners, and quality inspection professionals, establishing a comprehensive supply chain quality management system and conducting strict factory audits and pre-shipment inspections (PSI) are of utmost importance.
I. Source Control: Key Points for Factory Audit of Wire Suppliers
Before conducting bulk purchases, conducting a comprehensive supplier audit of wire manufacturers is the foundation for ensuring product compliance and safety.
Quality management system certification: Has the factory established and implemented the ISO9001 quality management system? Do they have complete procedures and records for incoming material inspection (IQC), production line inspection (IPQC), and final product inspection (FQC)?
Production qualifications and certifications: Verify whether the factory holds the necessary product certifications such as UL, VDE, CCC, CQC, etc., to ensure that the production capacity meets international standards.
Raw material control: Verify the qualifications and test reports of suppliers for copper, aluminum, and insulating materials (such as PVC, rubber, etc.), ensuring that the raw materials comply with environmental protection requirements such as ROHS and REACH.
Laboratory testing capabilities: Does the factory have equipment such as conductor resistance testers, insulation withstand voltage testers, and flame retardancy testing equipment, enabling internal testing of key items?
Production process control: Evaluate the technical proficiency of processes such as drawing, twisting, insulation extrusion, and winding, and inspect the workshop environment and equipment maintenance status.
II. Finished Product Inspection: Sampling Inspection Standard Process for Electrical Wires
The inspection of electrical wires should follow the AQL sampling standard (usually LEVEL II) and conduct random sampling, covering multiple aspects such as structural dimensions, electrical performance, mechanical performance, and safety performance.
1. Visual & Structural Inspection
Appearance quality: Check whether the insulation surface is smooth and flat, without dents, impurities, bubbles, or indentations; the color should be uniform and consistent.
Structural dimensions: Use a micrometer to measure the diameter of the conductor, the thickness of the insulation, and the thickness of the outer sheath. Check whether they comply with the AWG standard or metric specifications.
Identification and printing: Check whether the printed content on the label (such as specifications, certification marks, manufacturer codes, etc.) is clear, accurate and continuous.
2. Electrical Performance Testing - Core Inspection Item
Conductor Resistance Test: Use a DC resistance tester to measure the resistance value of the conductor at 20°C. The results must comply with the requirements of standards such as IEC 60228 or ASTM B193. This is a key indicator for determining whether the conductor material and cross-sectional area meet the standards.
Insulation resistance test: Apply a 500V DC voltage on the high-resistance meter and measure the resistance between the conductor and the insulation layer. Usually, it is required to be > 100 MΩ·km.
Withstand Voltage Test (Hi-Pot Test): A specified alternating voltage (such as 1500V/3000V) is applied between the conductor and the insulation layer for a duration of 1 minute or longer at a voltage level of 1 second or higher, without any breakdown phenomenon. This is a mandatory item in the safety test.
3. Mechanical and physical performance tests
Insulation adhesion: Check whether the insulation layer is tightly bonded to the conductor without any loosening.
Bending test: This assesses the fatigue resistance of the wire after being bent multiple times. The insulation layer should not have any cracks.
Aging test (selective): Place the wire in a high-temperature oven (e.g. at 113°C) for a certain period of time (e.g. 7x24 hours), and then test the rate of change in the tensile strength and elongation of the insulation.
4. Safety & Compliance Check
Verification of certification marks: Confirm that the certification marks on the cable (such as UL, VDE, CSA) are consistent with the provided certification documents.
Material verification: By cross-referencing material certificates or using an XRF analyzer for rapid screening, ensure that the materials meet environmental protection requirements (such as lead-free, halogen-free, etc.).
Specification conformity verification: This is the core of the inspection process. The working current (I = P/U) must be calculated based on the rated power (P) of the electrical appliance and the rated voltage (U) of the target market. Then, the AWG specification or the nominal cross-sectional area of the selected wire should be checked to ensure it has sufficient current-carrying capacity.
Example: An 1500W hot air gun for export to the United States (120V) has a working current of approximately 12.5A. According to the standard, a 16AWG cable (with an area of approximately 1.31mm²) with a carrying capacity of at least 13A should be selected. If a 18AWG cable (with a carrying capacity of approximately 8-10A) is mistakenly used, it will cause the wire to overheat and pose a fire risk (Critical defect).
III. Common Defect Classification
Critical (Severe Defect): Excessive conductor resistance (suspected of shoddy workmanship), breakdown during withstand voltage test, mismatch between specifications and power (insufficient wire diameter), absence of safety certification or non-compliance with certification.
Major Defects: Insulation thickness insufficient, printed characters unclear or incorrect, severe appearance defects, structural dimensions out of tolerance.
Minor (minor defect): Slight color difference, slight stains, poorly packaged in carton.
IV. Inspection Rules and Criteria
Sampling Plan: Based on the incoming batch quantity, a certain length of cable samples will be randomly selected and subjected to destructive tests (such as structural inspection and electrical tests) in accordance with the AQL standard (typically LEVEL II).
Defect determination: If one Critical defect is found, the entire batch can be deemed non-conforming. If the number of Major or Minor defects exceeds the AQL acceptance limit, it can also be classified as non-conforming.
Report Output: The detailed inspection report should include the sample size, various test data, defect descriptions (with attached pictures), and the conclusion regarding compliance with standards/specifications.
Conclusion
Although the wires are small, the responsibility is significant. The quality control of these wires must be systematic and strict. From the assessment of suppliers at the source and the factory inspection to ensure their ability to produce compliant products, to the final random inspection before shipment (FRI), using professional equipment to objectively verify key performance, this is the cornerstone for avoiding electrical fire risks, protecting brand reputation, and fulfilling product responsibilities. Do not let wires become the forgotten corner in the electrical inspection process. Mastering these key points of inspection and testing will make your supply chain management safer and more stable.