Factors affecting the insulation resistance of wires and cables

The phenomenon of low insulation resistance is often encountered in cable production, and there are many factors that affect the insulation resistance value of cables. In fact, there are four main factors that have a significant impact on the insulation resistance coefficient.

1.  The influence of temperature

As the temperature increases, the insulation resistance coefficient decreases. This is due to the increase in thermal motion, which leads to an increase in the generation and migration of ions. Under the action of voltage, the conduction current formed by ion movement increases, and the insulation resistance decreases.

Theory and practice have shown that the insulation resistance coefficient decreases exponentially with increasing temperature, while the conductivity increases exponentially with increasing temperature.

2. The influence of electric field strength

When the electric field strength is within a relatively low range, the migration rate of ions increases proportionally with the increase of electric field strength. Ionic current and electric field strength follow Ohm's law. When the electric field strength is relatively high, as the electric field strength increases, the migration rate of ions gradually changes from a linear relationship to an exponential relationship. When the electric field strength approaches breakdown, a large amount of electron migration occurs, resulting in a significant reduction in the insulation resistance coefficient.

The withstand voltage test voltage for various wire and cable products specified in the standard is in the stage where ion mobility increases proportionally with electric field strength, so the influence of electric field strength on insulation resistance coefficient cannot be reflected. When the sample undergoes a breakdown test, the influence of the electric field on the insulation resistance coefficient is reflected.

3. The influence of humidity

Due to the high conductivity of water, the size of water molecules is much smaller than that of polymer molecules. Under the action of heat, polymer macromolecules and constituent chains move relative to each other, allowing water molecules to easily penetrate into the polymer, increasing the conductive ions in the polymer and reducing insulation resistance.

This standard specifies immersion tests for various wires and cables. For example, before measuring insulation resistance, the rubber specimen is soaked in water for 24 hours. The purpose is to assess the impact of moisture and water on electrical performance during use.

Insulation resistance is one of the main electrical properties of insulation materials and an important indicator of wire and cable products or materials. Usually, the insulation resistance requirement is not lower than a certain value. If the insulation resistance value is too low, the leakage current along the wires and cable lines will inevitably increase, resulting in energy waste. At the same time, electrical energy will be converted into thermal energy, preparing for thermal breakdown and increasing the possibility of thermal breakdown.

4. The influence of material purity

Impurities mixed into the material increase the conductive particles and reduce the insulation resistance. Therefore, the insulation resistance of a certain rubber material will reflect the purity of the material and verify whether it meets the standards.

During the production process of wires and cables, if the process does not strictly follow the operating procedures, mixed impurities and materials may bubble due to moisture, insulation core deviation, or outer diameter size smaller than the standard, insulation delamination or cracks, insulation scratches, etc. It will reduce the insulation resistance of the product.

Therefore, in order to check the insulation resistance, it is necessary to check whether there are any problems in the process operation. During the use of wires and cables, measuring changes in insulation resistance can also help check for insulation damage and prevent accidents from occurring.