Electrical Cable Quality Control and Testing Scheme

Wone Store

07/31/2025

I. Problem Background
Electrical cables are the core transmission medium of power systems. Their quality performance directly determines the entire system's power supply stability, operational safety, equipment lifespan, and ability to prevent safety accidents such as fires. Substandard cables lead to a series of severe problems, including increased resistance, excessive heat generation, insulation breakdown, heightened fire risk, and aggravated signal interference. Therefore, establishing a scientific, rigorous, comprehensive quality control and testing system covering raw materials to finished products is crucial.

II. Scheme Objectives

Source Guarantee: Ensure all raw materials used in cable production comply with the highest national and industry standards (e.g., GB/T 3956, GB/T 12706, GB/T 19666, etc.).
Process Control: Effectively monitor key process parameters and the quality of intermediate stages during production.
Product Reliability: Ensure all key performance indicators of finished cables - including electrical, physical & mechanical, and fire performance - meet or exceed design and contract requirements.
Risk Management: Identify potential defects through systematic testing to prevent non-conforming products from entering the market and mitigate usage risks.
Traceability: Establish a complete quality testing record system to achieve traceability of key material batches and product test results.

III. Core Solutions: Electrical Cable Quality Control and Testing

(A) Raw Material Quality Control and Testing (Source Control)

1. Supplier Qualification and Evaluation:

Select qualified suppliers with a sound Quality Management System (e.g., ISO 9001 certification), stable supply capability, and good industry reputation.
Conduct periodic unannounced sampling inspections or third-party verification of supplier materials.

2. Key Raw Material Testing:

Conductor Material (Copper/Aluminum Rod/Wire):

Test Items: Chemical composition analysis (copper content, impurity elements), mechanical properties (tensile strength, elongation, repeated bending), resistivity measurement (at 20°C).
Standard Reference: GB/T 3953 (Round Copper Wire for Electrical Purposes), GB/T 3954 (Aluminum Rods for Electrical Purposes), GB/T 3956 (Conductors of Insulated Cables), etc.
Test Methods: Chemical analyzers (e.g., spectrometer), tensile testing machine, Wheatstone bridge, or precision resistance meter.

Insulation and Sheath Materials (PVC, XLPE, PE, LSZH, etc.):

Test Items:

Physical Properties: Appearance, density, thickness uniformity, tensile strength & elongation at break, performance comparison before/after aging.
Electrical Properties: Volume/surface resistivity.
Thermal Properties: Heat deformation, hot set test (for XLPE), low-temperature impact/bend test.
Fire Performance (for LSZH/Flame Retardant Materials): Oxygen index, smoke density, acid gas content, halogen content (for halogen-free requirement).

Standard Reference: GB/T 8815 (Unplasticized Polyvinyl Chloride Compounds), GB/T 15065 (Crosslinked Polyethylene Insulation Compounds), GB/T 18380 (Tests on Electric Cables Under Fire Conditions - Single Flame Test), GB/T 17651 (Measurement of Smoke Density), GB/T 17650 (Halogen-free, Low-smoke Materials and Products), and other applicable standards.
Test Methods: Universal material testing machine, aging oven, resistivity tester, hot set test device, oxygen index analyzer, smoke density chamber, chemical analyzers.

Shielding Material (Copper Tape/Wire): Thickness, resistance, coverage rate.
Filling/Bedding Materials: Water resistance (if applicable), mechanical strength, compatibility.

3. Testing Requirements:

All incoming raw materials must be accompanied by the supplier's Certificate of Analysis (COA)/Certificate of Conformity (COC).
Perform batch sampling inspection upon receipt based on defined sampling plans (e.g., GB/T 2828.1). Sampling frequency may be increased or full batch inspection implemented for critical materials (e.g., conductor, main insulation material).
Raw materials failing inspection are strictly prohibited from use in production.

(B) Production Process Quality Control (Process Monitoring)

1. Key Process Parameter Monitoring:

Conductor Stranding: Lay ratio, outer diameter, compaction (conductor).
Extrusion Process: Temperature settings and control per zone, extrusion pressure, line speed, cooling process (significantly impacts crystallinity).
Cross-linking Process (for XLPE): Irradiation dose/vulcanization temperature & time (critical for degree of cross-linking), cooling conditions.
Shielding Process: Coverage rate, overlap quality.
Cabling: Lay length, core stability.
Sheath Extrusion: Thickness uniformity, surface quality, printing legibility.

2. Process Sampling:

Establish online or offline inspection points at critical stages (e.g., after extrusion, cross-linking, cabling, sheathing).
Common Sampling Items: Insulation/sheath thickness and eccentricity, outer diameter, structural dimensions, appearance (surface defects), spark test / withstand voltage test (online/offline), partial physical property sampling (e.g., tensile).

(C) Finished Cable Quality Control and Testing (Final Verification)

1. Type Testing (for new products or first batch of important contracts): Perform all tests specified in relevant standards (e.g., GB/T 12706.1/2) to comprehensively verify design conformity.
2. Routine Tests (Per Batch / Per Drum / Per Reel):

Core Items:

Conductor DC Resistance Test: Measure the resistance of each conductor to verify compliance with nominal cross-section requirements (GB/T 3956). This is fundamental for ampacity and heating calculations.
Partial Discharge Test (Essential for MV/HV cables): Detect minute defects within the insulation that may lead to long-term failure (GB/T 3048.8, GB/T 12706). Extremely Important!
Voltage Test (Withstand Voltage Test):

Power Frequency AC Withstand Voltage: Most common. Apply multiple rated voltage (e.g., 2.5U₀) for a specified duration (e.g., 5 min). Insulation must not break down.
DC Withstand Voltage (Specific applications): Used for certain cable types or as a supplement to AC tests.

Insulation Resistance Measurement: Measure the resistance between conductor and shield/metallic sheath/earth, reflecting the insulation material's basic insulating properties (GB/T 3048.5/6).

3. Sample Tests (Batch Sampling or Periodic Tests):

Electrical Performance:

Capacitance measurement (if applicable).
Dielectric loss tangent (tan δ) measurement (especially for HV cables).

Structural Dimensions and Physical Properties:

Insulation and sheath thickness measurement: Ensure compliance with minimum design requirements.
Outer diameter measurement: Control tolerances.
Physical & Mechanical Performance Tests:

Tensile Strength and Elongation at Break (insulation/sheath) before/after aging: Key indicators, reflecting material's anti-aging capability and toughness (GB/T 2951.1).
Hot Set Test (Essential for XLPE insulation): Verify the degree of cross-linking compliance (GB/T 2951.21).
Low Temperature Impact/Bend Test: Assess material brittleness at low temperatures.
Flexing/Bending Test: Simulate installation and operating conditions to test cable flexibility (GB/T 12527).

Bending Test: Verify the cable's minimum allowable bending radius (usually performed on finished cable).
Fire Performance Tests (As per design requirements):

Single vertical flame test (GB/T 18380.1 series).
Bunched flame test (GB/T 18380.3 series).
Smoke density test (GB/T 17651).
Halogen-free, Low-smoke performance tests (Acid gas content, pH value, conductivity, light transmittance, halogen content - GB/T 17650).

Structural Examination: Conductor structure, shield coverage rate, core arrangement, filling density, metallic armor layer (dimensions, lay length, overlap gap), etc.

4. Testing Process:

Assign unique identification per finished cable batch/drum/reel.
Select representative samples according to defined sampling plans (per GB/T 2828.1 or contract requirements).
Conduct tests in accredited laboratories, adhering to current and valid national standards, industry standards, enterprise standards, or contract technical agreements.
All test items must have clearly defined pass/fail criteria.
Record test results in the finished product test report.

(D) Third-Party Verification and Inspection (Optional but Recommended)

For major projects, high-value cables used in critical locations, or upon specific user request:

Engage accredited independent third-party testing institutions (e.g., with CNAS/CMA accreditation) to perform sampling/re-testing of incoming materials or finished products.
Commission professional inspection agencies to witness and conduct on-site observation (audit/surveillance) during cable production (especially key processes) and final testing.

IV. Quality Testing Agency and Equipment Assurance

Accreditation: Laboratories performing testing tasks must possess relevant accreditation (e.g., CNAS, CMA).
Equipment Requirements: Equipped with comprehensive, fully functional testing equipment of requisite accuracy, regularly calibrated and verified (according to JJG procedures):

High-voltage test equipment (Power Frequency AC, DC, Impulse, Partial Discharge Systems).
Precision Bridges, Resistance Meters.
Universal Material Testing Machines (with high/low temperature chambers and aging ovens).
Hot Set Test Apparatus.
Fire Test Equipment.
Precision Measuring Tools (Calipers, Projectors).
Chemical Analysis Instruments (Spectrometer, Titrator, Ion Chromatograph, etc.).
Thickness Gauges (Laser, Ultrasonic).

Personnel Requirements: Testing personnel must be professionally trained, proficient in standards and operating procedures, and hold valid certification.

V. Non-Conforming Product Handling

Identify and isolate any product found non-conforming during any stage (raw material, process, finished goods).
Conduct non-conformance review to analyze the root cause.
Based on the review conclusion, implement one of the following actions: Re-work/Repair (if feasible upon evaluation and core performance is unaffected), Downgrade/Use as Concession (only for non-critical scenarios with user approval), or Scrap.
Strictly prohibit non-conforming products from reaching the project site in any form.

VI. Records and Traceability

Establish complete electronic and physical backup records of all inspections, including at least:

Raw Material Supplier Information, Batch Number, Purchase Order Number, Raw Material Test Reports.
Production Batch Number, Operation Logs (Key Parameters), Process Inspection Records.
Finished Product Identification (Type, Specification, Length, Manufacturing Date, Batch/Drum/Reel No.), Complete Finished Product Test Report (covering all mandatory and optional test results), Copy of Type Test Report (if applicable).
Third-Party Test/Inspection Reports.

Maintain archives for the defined period (typically not less than the product's expected lifecycle) to ensure product quality traceability. In case of quality issues, enable rapid tracing back to raw material batches, production conditions, and test data.