How to Understand the Two Formulas for Overload Protection in Low-voltage Distribution Lines

He Xiangkun（China Electric Design and Research Institute，Beijing 100048，China）

Abstract Aimed at how to understand the overload protection formulas in section 4 ． 3 ． 4 of Code for Design of Low-voltage Electrical Installations（GB 50054 - 95），through analysis of the relevant native and foreign standards and specifications，combined with the calculation examples，the meaning and use of the overload protection formulas for low-voltage distribution lines are explained.

Key words　Low-voltage distribution line　Overload protection　Circuit breaker　Fuse

摘　要　针对《低压配电设计规范》（GB　50054　-　95）中第　4 ． 3 ． 4　条过负荷保护公式如何理解的问题，通过分析国内外相关标准规范，并结合计算实例，说明低压配电线路过负荷保护公式的含义和使用。

关键词　低压配电线路　过负荷保护　断路器　熔断器