A Voltage Drop and Load Flow Study is performed to determine if the conductors are sufficiently sized to deliver electrical power without adding excessive impedance to the system. The NYC Electrical Code in Article 215.2(A) requires feeder conductors to be sized such that the voltage drop does not exceed 3%. The NYC Energy Code in Article 8.4.1 states that the total voltage drop at the last branch circuit device cannot surpass 5%.
The current is calculated from electrical load calculations. The impedance is calculated from the feeders and transformers. The length, size, quantity, and material of the conductor all contribute to the overall system impedance. Once all this information is available, the voltage could then be calculated. At 208V, it is a code violation to have less than 197.6V at an electrical outlet. Load Flow calculations allow you to determine if the ampacity of the conductors are rated sufficiently to carry the calculated load.
In the event where the voltage drop surpasses 5%, electrical motors and HVAC equipment may fail to operate. It is difficult to resolve Voltage Drop issues after a building has been constructed, so it is advisable to have the Voltage Drop Study completed prior to installing the electrical system.