Voltage Drop Considerations

Voltage drop calculations should be performed over the entire circuit from the POCO (Power Company) to the branch circuit panels. Upsizing conductors for voltage drop from the POCO to the first disconnect is acceptable, as this will reduce the voltage drop over that section.

Conductors to Branch Circuit Panels

The circuit conductors extending from the first disconnect to the branch circuit panels must be sized to handle the total amperage of the loads within those panels. The amperage of the loads at each branch circuit panel can be summed to determine the required conductor size. It is not required to maintain the upsized conductor size throughout the entire circuit if the amperage of the loads decreases at each branch circuit panel.

Parallel Conductors

Running two parallel 500kcmil AL conductors to the 400A meter/disconnect is acceptable. The current-carrying capacity of the parallel conductors is equal to the sum of their individual capacities. If you intend to run two sets of 250kcmil AL conductors from the disconnect to the two interior breaker panels, ensure that each set of conductors is sized appropriately for the amperage of the loads in the respective panel.Based on your description, the following is a possible layout:

Meter/Disconnect

Two parallel 500kcmil AL conductors

Interior Panel 1

One set of two 250kcmil AL conductors (sized for the amperage of the loads in this panel)

Interior Panel 2

One set of two 250kcmil AL conductors (sized for the amperage of the loads in this panel)

Note: The maximum allowable distance for parallel conductors is 30 feet (9.14 meters).* You should consult local electrical codes and regulations for specific requirements in your area. Flag for review