Virtarajat

Virtarajat refers to the maximum electrical current that a conductor, cable, component, or system can carry continuously without exceeding its temperature rating. They are essentially a thermal constraint: current causes heat, and if the temperature rise is too high due to ambient conditions or limited cooling, the allowable current must be reduced. Virtarajat are not the same as voltage ratings or short-circuit ratings, but they interact with how a system handles heat during operation.

Determination of virtarajat is based on ampacity, which is specified in standards for particular materials, sizes, insulation types, and installation conditions. Typical tables define nominal values for copper or aluminum conductors under specified ambient temperatures and installation methods (in air, in conduit, buried, etc.). Engineers apply derating factors for high ambient temperatures, crowded cable runs, or restricted ventilation. There are continuous ratings for normal operation and sometimes a separate short-term or peak rating for temporary overloads. In equipment design, short-circuit current rating (Isccr) and device protection settings are also linked to the concept of virtarajat, though they describe different protective limits.

Application and safety: Virtarajat guide the sizing of cables and protective devices to keep temperatures within safe limits, protecting insulation, reliability, and safety. Exceeding virtarajat can cause insulation damage, reduced lifespan, or fire risk. National and international standards—such as IEC, EN, or NEC-based guidance—provide the detailed tables and derating rules used by electricians and engineers to determine appropriate current ratings for a given installation.

In electronics contexts, a device may implement an internal current limit to prevent overheating, which is a component-level form of virtarajat.