As is known, the “two wires–rail” power supply system (TWR line) does not meet the modern electromagnetic compatibility requirements, which is a factor causing increased damageability of alarming, centralized control and interlocking devices, as well as other non-traction electric power consumers. In addition, there often occur unexplained differences (unbalance) in the accounting of electricity received by end users and consumed by the TWR line at a traction substation. The accomplished studies have shown that in almost all sections of the network, the actual electricity consumption is significantly lower than that recorded by the TWR line metering devices. The discrepancy in the readings could be explained by unauthorized taps of electricity. However, such a statement will be superficial. The article considers the real factors causing the unbalance in accounting the electricity consumed on the TWR line, which are explained by the magnetic influence of the contact system. An equivalent circuit of the contact system magnetic influence on the TWR line is presented for any configuration of the section with different placements of self-contained transformer substations at different levels of their power capacity. The magnetic influence of the contact system on the TWR line is illustrated by a phasor diagram.