What is the 80% rule for electrical circuits?

The 80% rule for electrical circuits is an important safety guideline primarily used to guide circuit load design and avoid overload risks. This design principle is reflected in the GB 19517 series of electrical safety technical specifications, with its core purpose being to reserve a 20% safety margin for the operation of electrical equipment to cope with uncertain factors such as instantaneous peak currents and ambient temperature changes. In the industrial sector, this rule is directly related to the requirements for conductor temperature rise limits (e.g., enclosure ≤ 60K) in the GB 5226.1 standard; for temporary electrical use in construction, the JGJ/T46-2024 standard also indirectly embodies this principle through power distribution system design. The 80% rule applies not only to main circuit design but also needs to be followed in links such as the selection of distribution box circuit breakers and the calculation of cable cross-sectional area, forming a technical closed loop with the requirements for electrical equipment safety protection in the GB/T 16895.22 standard. For Malaysia's automotive circuit systems, this rule is particularly important in the power supply design of high-power equipment such as on-board charging modules and electric compressors, which can prevent safety hazards caused by overheating of lines.