Real circuits are chains: service → panel → subpanel → load, often in different wire sizes carrying different currents. Build the chain segment by segment and watch the cumulative drop against the 5% total budget.
The NEC's 5% recommendation covers the entire path from service equipment to the farthest outlet. A common allocation is 2% for the feeder and 3% for the branch — but any split works as long as the sum stays inside the budget. This tool computes each segment with its own conductor size and current (downstream segments usually carry less), then accumulates the total so you can see exactly where the volts go.
Because load divides along the path. A 100 A feeder might serve a subpanel from which only 24 A continues to the workshop circuit you care about — each leg drops voltage according to the current it actually carries.
That is the point — feeders are large, branches are small. Each segment row takes its own AWG size, and the totals combine correctly.