# Derating of Electrical Contacts with Varying Surface Roughness
## 1 Introduction
For instance, in high-humidity environments, there is an increased risk of corrosion, which raises contact resistance and reduces conduction efficiency [17]. Derating takes these factors into account, reducing the load on contacts to extend their lifespan and reliability in such conditions [18]. The use of derating in electrical contacts is significant in various fields, such as the automotive, aerospace, energy, and consumer electronics industries [12; 16; 19]. In these sectors, system reliability is critical, and failures resulting from insufficient protection of contacts can lead to severe consequences, including equipment damage, financial losses, or threats to human life and safety. In summary, derating in electrical contacts is a design strategy that involves intentionally reducing maximum operating parameters relative to nominal values to enhance the reliability and durability of contacts under actual operating environments. This process considers factors such as changes in contact resistance, thermal effects, environmental factors, and mechanical wear [14; 20]. Through derating, electrical systems can operate more reliably and safely, even in challenging operating conditions. Derating in the context of machined electrical contacts refers to the necessity of reducing the rated parameters of these components, such as maximum current, voltage, or power dissipation, to ensure their reliability and durability under non-ideal conditions. Machined electrical contacts, produced through mechanical processing, have specific surface and geometric properties that directly affect their electrical and thermal performance [3; 7; 15] and the required level of derating [18]. The turning process plays a crucial role in shaping the contact surface, which is one of the most important factors affecting the performance and reliability of electrical contacts. Ideally, the contact surface should be smooth and free from defects to minimize contact resistance and energy losses. However, turning, as a method of mechanical machining, often leaves surface micro-roughness and chip patterns that can influence contact quality. Surfaces with high roughness reduce the actual contact area, leading to localized increases in current density and heat generation, raising the risk of overheating and material degradation [21]. Surface irregularities created during turning can also impact the mechanical properties of contacts. High localized stresses at contact points can accelerate mechanical wear processes such as material fatigue or abrasion, further increasing contact resistance and decreasing conduction efficiency. Consequently, derating is necessary to minimize the risk of failure caused by heat accumulation and surface degradation [22]. Turning also affects the chemical properties of contact surfaces, which is significant in the context of derating. The machining process may leave residues of oils, contaminants, or oxides on the surface, increasing contact resistance. The high operating temperatures resulting from increased resistance can accelerate oxidation or corrosion, particularly in harsh environmental conditions such as high humidity or the presence of aggressive chemical substances. To mitigate these effects, the operating parameters of contacts are deliberately reduced, accounting for additional safety margins [22]. The geometry of turned contacts also directly impacts derating. Turning enables precise shaping of contacts; however, slight deviations from the ideal shape can affect the uniformity of pressure and current distribution on the contact surface. In cases where contact pressure is too low or uneven, the actual contact area decreases further, leading to localized current concentrations and accelerated heating in those regions. As a result, the current flowing through the contact must be limited, reflected in the derating values [23]. Another critical aspect is the impact of turning on heat dissipation from electrical contacts.