Understanding Arc Resistance and How to Test It

Arc resistance on gray volt meter at 414

Electric currents or charges cannot travel freely through electrical insulator materials. Electrons have extremely little flexibility to drift from atom to atom in electrical insulator materials.

When selecting a material for electrical insulation, you depend on its protection. 

As an illustration, you’ve probably noticed that the outside of your phone charger plug is plastic to prevent electric charges from passing through to human flesh. Well, you can thank arc resistance for that. 

These are some of the most used electrical insulators:

  • Styrofoam
  • Plastic
  • Porcelain
  • Wax
  • Rubber
  • Dry air
  • Glass
  • Ceramics
  • Teflon
  • Mica
  • Asphalt

Keep in mind that you shouldn’t insulate electricity using easily combustible, highly conductive materials. You must test each substance using scientifically proven procedures.

With that said, here are the fundamentals of arc resistance. 

Related: Types of Electrical Grounding Systems & Techniques

What is Arc Resistance?

The ability of an insulating material to endure a high-voltage electric arc and resist the creation of a conducting route over its surface is known as arc resistance.

Thermal and chemical degradation and erosion of the substance produce this conducting route. Plastic materials with strong arc resistance qualities are chosen to handle situations vulnerable to electric arcing.

When a high voltage source of current causes a leakage or fault channel through the surface of an insulating material, a carbonized path forms slowly, appearing as a thin line between two electrodes.

Since arc resistance varies from material to material, the comparisons that are done between them need to be in the quantifying property of time units.

When materials are exposed to a high voltage, low current arc close to their surface, this is stated as the number of seconds it takes for an electrically conducting channel to form along its surface.

As a result, it is an ultimate source of arc resistance distinction between various plastic materials. That’s why data centers need to have an ample amount of experts who handle all energy consumption efficiently. 

Related: What is Arc Flash? What to Know for Prevention

Electric Arc Failure of Plastic Materials

The failure of plastic materials due to arcing happens by the following:

Materials Become Incandescent

When exposed to high-voltage electric arcs, many inorganic dielectric materials turn incandescent. 

When an object becomes incandescent, it is emitting electromagnetic radiation from its hot body due to its high temperature.

This, in turn, makes the object the ability to conduct electric currents. Nevertheless, the material will regain its insulating characteristics after cooling.

Becomes Too Hot

Few organic compounds catch fire without leaving a noticeable conducting trail across the surface.

Carbonization of Surface

Once there is enough carbon to transmit the electric current across the material, the last kind of failure happens through the carbonization of the surface.

Other Elements Affecting Arc Resistance

Cross-section of the Arc

The arc resistance increases as the cross-sectional area of the arc decreases.

Length of the Arc

The arc resistance rises as the arc length or the distance between the contacts increases.

Degree Of Ionization

The arc resistance rises as the number of ionized particles between the contacts decreases.

How To Test Arc Resistance

The ASTM D495, a standard method using a high-voltage, low-current set-up under dry conditions, is provided to test various materials for arc resistance.

Keep in mind that this method is generally not used to rank the relative arc resistance of materials exposed to different arcs, such as low-voltage arcs at low or high currents.

The dry arc resistance test is used for three purposes because of its convenience and low testing time:

  • Testing for quality assurance
  • Materials are screened first.
  • Detecting the impact of formulation changes

The test is normally performed in a clean, dry laboratory environment that is rarely encountered in the field.

As a result, the forecast of a material’s relative performance in typical applications and shifting from clean to filthy environments may be significantly influenced.

There are also criteria for arc resistance testing in both wet and dry circumstances if necessary.

Related: What is HIPOT Testing? Dielectric Strength Test Explained

ASTM-D495 for Polymer Arc Resistance

Test Method ASTM D 2132, D 2303, and D 3638 analyze wet, contaminated materials, while ASTM-D495 evaluates dry, uncontaminated samples.

For engineering purposes, the ASTM recommends this extra testing. They should assist ASTM-D495 in determining the importance of quality control.

Materials that cannot form a conductive route in reaction to an electric arc are exempt from the ASTM-D495 test.

Materials that leave fluid residues or melt should not be utilized because they inhibit the formation of a conductive route.

Need help with your data center? Book a strategy call with us to assist you with everything from infrastructure design and power to cooling technologies and specialized cleaning services.

Electric Arc Failure in Plastics and Methods to Improve Arc Resistance

Many inorganic materials become incandescent when exposed to an electric arc, resulting in electric current conductivity. However, they revert to insulators when cooled. 

Another factor is surface carbonization, which occurs once enough carbon is present to transmit electric current across the material.

Different polymers have varying levels of arc resistance. 

Thermoset phenolics are prone to carbonization and so have low arc resistance. On the other hand, alkyds, melamine, and fluorocarbons are good arc-resistant materials.

The inclusion of reinforcements such as fiberglass, minerals, and other inorganic fillers can significantly improve the arc resistance of thermoplastics.


Electric arcing is a tough problem that can negatively impact the electric power of your data center, as well as the distribution and electronic equipment.

Now that you know what arc resistance is and how to test it, it’s essential that you choose the best materials for your data center. This will lower the risk of equipment damage, and fire suppression and avoid human danger.

Completely understanding arc resistance may take more time and research, but knowing what the measurement indicates is critical for the safety and efficiency of processes in many industries.

If you have any questions about electrical insulating materials, reach out to our team at C&C Technologies today!

Last Updated on June 8, 2023 by Josh Mahan

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