There are three different test methods used for Electric Strength testing and Breakdown Voltage testing on winding wires. Before diving into the specific test methods, it’s important to understand the difference between these two types of tests.

Understanding the Test Types

Electric Strength Tests

These are pass/fail tests where the wire must withstand the application of a test voltage for a specified period. Key characteristics:

• Test voltage is applied for a set duration
• Wire must not break down during the test period
• Testing stops after the specified time
• Failure occurs if breakdown happens before test completion

Breakdown Voltage Tests

These tests measure the voltage at which insulation failure occurs. Key characteristics:

• Test voltage is steadily increased at a specified rate
• Testing continues until breakdown occurs
• The voltage at breakdown is recorded as the result
• Typically performed on five samples

Test Methods According to IEC 60851-5

Let’s examine the three different test methods used for both Electric Strength and Breakdown Voltage testing.

1. Metal Cylinder Test Method

Applicable for: Overall diameters up to 0.1mm

Test procedure:

• A straight piece of wire has insulation removed from one end
• Wire is wrapped once around a polished metal cylinder (25mm diameter)
• Load specified in IEC 60851-1 maintains wire contact with cylinder
• Test voltage is applied between wire and metal cylinder

Reference: IEC 60851-5 Clause 4.3

2. Twisted Pair Test Method

Applicable for: Overall diameters >0.1mm and up to 2.5mm

Test procedure:

1. Sample preparation:

   • Wire has insulation removed from both ends
   • Bent into U shape
   • Twisted back on itself
   • Specific number of twists applied over ~125mm length
   • Bottom loop cut and separated

2. Testing:

   • Test voltage applied between the two twisted conductors
   • Test voltages typically double other methods (due to dual insulation)

Reference: IEC 60851-5 Clause 4.4.1

3. U-Bend Metal Shot Bath Test Method

Applicable for: Overall diameters >2.5mm

Test procedure:

• Wire bent into U shape with specified bend radius
• Sample placed vertically in plastic bucket
• Bucket partially filled with metal shot (steel, nickel, or nickel-plated iron)
• Additional shot poured to cover sample (90mm from U-bend bottom)
• Test voltage applied between wire and metal shot

Reference: IEC 60851-5 Clause 4.5.1

Special Applications

For higher voltage and specialty applications, custom electrical testing programs can be developed using the twisted pair and U-bend test methods. These custom programs can be tailored to specific application requirements while maintaining compliance with standard testing methodologies.

Key Considerations for Test Selection

When selecting a test method, consider:

1. Wire diameter - primary determining factor
2. Application requirements
3. Voltage rating of the wire
4. Specific standard requirements
5. Customer specifications

Test Method Selection Guide

Wire Diameter	Recommended Test Method
≤0.1mm	Metal Cylinder Test
>0.1mm to 2.5mm	Twisted Pair Test
>2.5mm	U-Bend Metal Shot Bath Test

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Need help determining the right test method for your winding wire application? Contact our knowledgeable sales and engineering teams to discuss your requirements at sales@rubadue.com or +1(970) 351-6100.