This book cover theory & practical examples about Voltage Drop & Cable sizing Calculations. AC & DC Breaker, Voltage drop and cable sizing calculation of real substation is included in this book for better understanding.Knowing about voltage drop and cable size calculations is always the important topic for Electrical Engineers, Technicians. I have covered topics from very basic concept and definitions to advance practical calculations. Basic theory is explained with examples that are very easy to understand. After understanding the basic concept we will further solve a basic calculation example for voltage drop and cable sizing of cable. Furthermore I have included AC & DC Breaker, Voltage drop & Cable sizing calculations of real 380kV Substation for review and better explanation. If you like to know how cable sizes are selected, what is voltage drop and its acceptable ranges, different type of installation method, what is bonding, why it is important to earthed the sheath of cable. Why cable is heat up and how to avoid it.