Electrical Testing for Plastics

A close-up image of a machine testing a piece of plastic.

Volume resistivity test

This method is used to determine the volume resistivity of an insulating material. The surface flows of the test specimen are eliminated using an electrode.

Test specimen	Ø 80 mm, 2 mm thick
Test voltage	Between 1 V and 1,000 V
Current measurement	10-1 A to 10-14 A
Temperature range	23°C to 200°C

Standards for volume resistivity
UL 746A, ASTM D257, IEC 62631, or equivalent standards

Results of the volume resistivity test method: Volume resistivity ρ (rho). This is the volume resistivity of an insulating material in the form of a cube whose edges measure 1 cm.

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Surface resistivity testing of plastics

This method is used to determine the surface resistivity of a test specimen. The volume flows of the insulating material are eliminated using an electrode.

Test specimen	usually Ø 80 mm, 2 mm thick
Test voltage	Between 1 V and 1,000 V
Current measurement	10-1 A to 10-14 A
Temperature range	23°C to 200°C

Standards for surface resistivity
UL 746A, ASTM D257, IEC 62631, or equivalent standards

Dielectric strength test

This method is used to assess the dielectric strength of an insulating material. It calculates the voltage at which a harmonic alternating voltage collapses upon destruction of the insulating material.

Test specimen	usually Ø 80 mm, 2 mm thick
Max. test voltage	100 kV (50 Hz)
Current on breaking	40 mA
Surrounding medium	Insulating oil
Electrode pairs	Plate/plate Ball/ball Ball/plate

Standards for dielectric strength
IEC 60243-1, VDE 0303-21, UL 746A, or equivalent standards

A close-up picture of a machine testing plastic.

Comparative Tracking Index (CTI) ASTM D3638

This method is used to assess the relative resistance of insulating materials to tracking.

CTI / tracking IEC 60112

This method is used to assess the relative resistance of insulating materials to tracking.

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High voltage tracking resistance (IPT)

This method can be used to assess the susceptibility to tracking of insulating materials that are exposed to high voltages outdoors.

Insulators installed in the open are often at the mercy of humidity. Their electrical insulation properties can deteriorate to such an extent as a result that tracking paths are formed on the insulator surface. This test determines the tracking resistance that defines the dielectric strength of the insulating material surface and the maximum allowable leakage current (tracking).

Test specimen	130 mm x 50 mm x 6 mm
Test voltage	2,5 kV, 3,5 kV, 4,5 kV (50Hz)
Test solution	0,15 ml/min at 2,5 kV 0,30 ml/min at 3,5 kV 0,60 ml/min at 4,5 kV
Failure criteria Method A:	Current exceeds 60 mA Specimen burns Hole is formed
Failure criteria Method B:	Tracking reaches mark (25 mm) Specimen burns Hole is formed Current exceeds 60 mA

Results of the high voltage tracking resistance (IPT) test method: The maximum test voltage at which five specimens each resist the stress for six hours without any of the failure criteria being met.

High-Current Arc Ignition (HAI)

The high-current arc ignition (HAI) test determines the number of arcs which are necessary to ignite a plastic material. This test is carried out on the plastic surface: 40 arcs per minute are ignited between a fixed and a movable electrode.

Standards High-Current Arc Ignition (HAI)
UL 746A

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