Voltage drop for branch circuits is automatically calculated by Design Master Electrical. There are two settings that can be used to change how the voltage drop is calculated. These settings are found at the bottom of the Looping Options dialog box.
DM Electrical 
Circuiting and Homeruns Set Looping Options
When the Compute Conduit Length Orthogonal to Building Angle option is not checked, the distance between devices is calculated using a straight line. The distance is therefore minimized. This setting may often be used on site plans, where the conduits do not have to follow the walls.
The default setting is for this option is checked. When it is checked, the distance between devices is calculated following the x and y axis. This setting is commonly used inside a building, where the conduits have to be run in the walls. The Building Angle determines the angle at which the conduit length is calculated when the orthogonal setting is checked. On a typical plan, the walls are horizontal and vertical on the screen, which corresponds to an angle of 0. If the building, or a section of a building, is rotated on the plan, this angle should be changed to match the angle of one of the walls. You may indicate the building angle either by typing in an angle in the Building Angle field, or by pressing Select Angle, which will take you to the drawing where you may click twice to select the building angle. This allows you to trace a wall of the building if the numerical value of the building angle is not known. After you have clicked on the drawing to indicate the angle, you will be returned to the Looping Options dialog box, which will then include the angle you chose in the Building Angle field.