Voltage Drop Tables
A number of electrical reference books contain voltage drop tables which allow the correct wire size to be determined if the desired voltage drop limit, maximum current, and distance from the source to the load are known. These tables are very convenient and do not require the use of the mathematical formulas. They do require you to find the appropriate voltage, phase, conductor material, and voltage drop table in order to determine the correct answer. This requires a large number of tables.
To use the tables, find the amperage in the left column and the length of run or distance between the source and load along the top of the table. If your number is between two of the table numbers, use the higher value. The row and column where they intersect on the table is the recommended wire size that will keep voltage drop within acceptable limits.
Using Voltage Drop Tables
* Wire Type: There are different tables for Copper and Aluminum wire.
+ Amperage: The maximum amperage this table can be used for.
D Voltage: The voltage rating for this table. There are different tables for each of the standard service voltages.
O Phase: There are different tables for Single and Three Phase power.
l Percent Voltage Drop: The allowable voltage drop limits for table. There are tables with other values.
Minimum Size of Conductor: * Copper, + Up to 200 Amperes, D115120 Volts, 0 Single Phase, l Based on 3% Voltage Drop
Example:
Find the size of copper wire to carry a load of 40 amperes at 120 volts a distance of 500 feet with 3% voltage drop. Use the Table: Note the column heading of the table: Copper, Single Phase, 120 volts, 3% voltage drop. Follow the first column "amperage" down to 40 amps. Find the 500 feet column in the table under length of run. Where the 40 amp row and 500 foot column cross, the wire size can be found. In this case, a 00 or 2 ought copper wire. This method of finding the correct wire size is simple when you have the right table.
