Condition monitoring approaches for railway point machines are often based on the analysis of motor current or power curves, with occasional consideration of external factors such as temperature. A critical underlying assumption in these approaches is the constancy of the voltage of the power supply. This study investigates the validity of this assumption by analyzing a dataset from a small railway yard, where both operational voltage and motor current curves were measured across all switches. The results reveal both long-term changes in no-load voltage and transient changes in operating voltage due to overlapping movements of multiple switches connected to the same power supply, challenging the conventional assumption of voltage constancy. While the impact of transient voltage fluctuations in the small yard studied is arguably minor, the potential implications for condition monitoring in larger railway yards are significant. This is indirectly quantified using a dataset from a large railway yard where motor current curves, but not operating voltage, are measured across all switches. This paper discusses the impact of voltage variability on existing monitoring techniques and proposes practical solutions to identify and address these issues.