The minimum size conductors permitted to be run between a generator and a distribution panelboard for a 3Ø, 300 kVA generator delivering 480 volts when conductors are run in parallel in two conduits is which of the following?

The minimum size conductors permitted to be run between a generator and a distribution panelboard for a 3Ø, 300 kVA generator delivering 480 volts when conductors are run in parallel in two conduits is which of the following?

• A. 350
• B. 4/0
• C. 250
• D. 3/0

Answer: (B)

The main idea is sizing feeders that run in parallel for a generator. When you have a 3-phase generator supplying a panel, you first find the running current and then account for how parallel paths share that load. Compute the generator current at 480 V: I = S / (√3 × V) ≈ 300,000 VA / (1.732 × 480 V) ≈ 360 A. With two parallel paths, the load splits roughly in half, so each path carries about 180 A. For conductors feeding a panel on a continuous-duty or otherwise uninterrupted basis, you size the conductors for 125% of the load. So per path you need an ampacity of 180 A × 1.25 ≈ 225 A. Check conductor ampacities (copper, 75°C column): 3/0 AWG is about 195 A (not enough), while 4/0 AWG is about 230 A (sufficient). Therefore, the smallest conductor size that meets the requirement is 4/0 AWG copper. This is why the correct choice is 4/0.

The main idea is sizing feeders that run in parallel for a generator. When you have a 3-phase generator supplying a panel, you first find the running current and then account for how parallel paths share that load.

Compute the generator current at 480 V: I = S / (√3 × V) ≈ 300,000 VA / (1.732 × 480 V) ≈ 360 A.

With two parallel paths, the load splits roughly in half, so each path carries about 180 A. For conductors feeding a panel on a continuous-duty or otherwise uninterrupted basis, you size the conductors for 125% of the load. So per path you need an ampacity of 180 A × 1.25 ≈ 225 A.

Check conductor ampacities (copper, 75°C column): 3/0 AWG is about 195 A (not enough), while 4/0 AWG is about 230 A (sufficient). Therefore, the smallest conductor size that meets the requirement is 4/0 AWG copper.

This is why the correct choice is 4/0.