ASTM D876

ASTM D876 covers the testing procedures for nonrigid polyvinyl chloride (PVC) tubing used specifically for electrical insulation applications.
This standard provides a set of test methods to evaluate the physical, mechanical, and electrical properties of the tubing to ensure it meets necessary performance and safety requirements.

This article explains the purpose of ASTM D876, the necessary testing equipment, common procedures, and related ASTM standards often referenced alongside it.

Purpose of ASTM D876

The main objective of ASTM D876 is to define the key tests required to ensure that flexible PVC tubing:

• Provides adequate electrical insulation.

• Maintains mechanical integrity (such as elongation and tensile strength).

• Withstands environmental stresses like heat, cold, and moisture.

Industries rely on ASTM D876 to qualify materials for use in electrical systems where nonrigid insulation is needed—such as in consumer electronics, automotive harnesses, appliances, and industrial equipment.

Equipment Required

Because ASTM D876 encompasses multiple test methods, a variety of testing equipment may be used:

• Universal Testing Machine (UTM):

  • Used for tensile strength and elongation tests.

• Dielectric Breakdown Tester:

  • Applies voltage to measure the material's electrical insulating properties.

• Aging Ovens:

  • For thermal aging resistance tests at elevated temperatures.

• Bend Test Fixtures:

  • For supporting the sample and adding the necessary stress.​

• ​Cold Temperature Chamber

  •  

    To determine flexibility and cracking resistance at low temperatures.​

     

• Micrometers and Calipers:

  • For precise measurement of tubing dimensions like wall thickness and internal diameter.

• Water Immersion Tanks:

  • For moisture absorption and hydrolytic stability testing.

Key Tests Performed Under ASTM D876

Several individual tests are included within ASTM D876. Some of the most important are:

1. Tensile Strength and Elongation:

   • Determine mechanical strength and ductility.

   • Specimens are pulled at a uniform rate until rupture.

   • Results reported as maximum tensile strength (psi or MPa) and percent elongation at break.

2. Dielectric Strength:

   • Measures the maximum voltage the tubing can withstand without electrical breakdown.

   • Expressed in volts per mil (V/mil) or kilovolts per millimeter (kV/mm).

3. Thermal Aging:

   • Exposes samples to high temperatures for a specified time.

   • Then retests tensile strength and elongation to measure property retention.

4. Cold Bend or Low-Temperature Flexibility:

   • Tubing is cooled to a low temperature (e.g., -20°C or lower) and bent around a mandrel.

   • Cracks or breaks are cause for failure.

5. Dimensional Verification:

   • Measures internal diameter, wall thickness, and concentricity to ensure physical consistency.

6. Water Absorption or Hydrolytic Stability:

   • Measures how much moisture the tubing absorbs under specified conditions.

   • Important for maintaining electrical insulating properties over time.

Test Specimens

• Test specimens are typically cut sections of tubing.

• For mechanical tests, tubing may be flattened or left cylindrical depending on test requirements.

• Conditioning before testing is important—specimens should be equilibrated at standard laboratory conditions unless otherwise specified.

Procedure Highlights

1. Conditioning:

   • Unless otherwise stated, condition specimens at 23°C (73°F) and 50% relative humidity for at least 40 hours before testing.

2. Testing Sequence:

   • Conduct mechanical tests (tensile and elongation) first on unaged specimens.

   • Subject specimens to thermal aging, then retest.

   • Perform dielectric strength tests, dimensional measurements, and any optional tests like cold bend.

3. Failure Criteria:

   • Tubing must meet minimum specified values for tensile strength, elongation, dielectric strength, and flexibility both before and after thermal aging.

   • Cracks during cold bend, low dielectric strength, or poor aging performance can result in material rejection.

Results and Reporting

A complete ASTM D876 report should include:

• Material description (compound type, lot number).

• Tensile strength and elongation (before and after aging).

• Dielectric strength values.

• Dimensional measurements.

• Visual observations (cracking, surface irregularities).

• Test conditions (temperatures, humidity, voltages, mandrel sizes).

• Pass/fail judgments based on criteria established by end users or product specifications.

Related ASTM Standards

Several other ASTM standards are closely related to or often referenced with ASTM D876:

• ASTM D2671 – Standard Test Methods for Heat-Shrinkable Tubing for Electrical Use:
  Similar to D876 but focused on tubing that shrinks under heat exposure rather than static PVC tubing.

• ASTM D3032 – Standard Test Methods for Hookup Wire Insulation:
  Involves electrical testing on wire insulation materials, which may include flexible PVC.

• ASTM D1248 – Specification for Polyethylene Plastics Extrusion Materials for Wire and Cable:
  Covers similar electrical insulating materials, but specifically polyethylene-based.

• ASTM D922 – Test Methods for Rubber Insulating Materials:
  Similar approach to electrical insulation testing but applied to rubber rather than plastics.

• ASTM D1056 – Standard Specification for Flexible Cellular Materials—Sponge or Expanded Rubber:
  Although focused on sponge rubber, D1056 shares some mechanical and environmental testing methods like tensile and cold flexibility.

Applications of ASTM D876 Testing

Nonrigid PVC tubing tested to ASTM D876 is commonly used in:

• Consumer electronics (cable harnesses, chargers, adapters)

• Automotive wiring (flexible conduit and wire protection)

• Household appliances (internal electrical insulation)

• Industrial equipment (control panel wiring, robotics)

• Medical devices (where flexible yet electrically insulating tubing is needed)

By verifying tubing performance against ASTM D876, manufacturers ensure long-term durability, flexibility, and electrical safety under a wide range of operating environments.