This paper contains analysis of a part of Russian Electrical Code called PUE. This paper describes a basic heat balance model for wires of GOST 839-80 (Russian equivalent of EN 50182). As a result, the current- carrying capacity of this model is much less than the current-carrying capacity of GOST 839-80. This means that the PUE requirements may be incorrect. A formula for determining the current-carrying capacity in this model, ready for use in engineering, is proposed. Tables of the current-carrying capacity for all wires of GOST 839-80 are given. This paper only analyzes the requirements of PUE for the current- carrying capacity of outdoor wire. The PUE requirements for the current-carrying capacity of indoor wires will be discussed in the next paper.