Power system analysis, protection, and earthing are interdependent disciplines that are critical to high-voltage network design. Yet, they are often conducted in isolation, introducing errors and reducing overall accuracy. Decisions made during the earthing design phase can directly influence fault current magnitudes and the performance of protection schemes. Conversely, power system modelling that relies on simplified or incorrect earthing assumptions risks generating inaccurate fault parameters, which can propagate errors into subsequent earthing and protection studies. This presentation investigates the impact of varying earthing impedances on fault levels and their consequences for protection coordination. By modelling different fault scenarios and protection schemes, it demonstrates how integrated studies can lead to more accurate analyses, improved coordination, and safer overall system performance. The findings highlight the necessity of a holistic design approach that accounts for the mutual dependencies between earthing, system modelling, and protection engineering.