Interpretation of Design Plans and Building Documents
This domain tests plan literacy: can you read the approved set, extract the design basis, and compare it with field conditions? You will see site plans, roof plans, single-line diagrams, equipment schedules, structural details, and specifications.
Documents to read together
- Cover sheet and code summary: adopted NEC edition, local amendments, design loads.
- Site and roof plan: array dimensions, setbacks, pathways, tilt, azimuth, mounting points.
- Single-line diagram: module count and string configuration, combiner, overcurrent device, disconnect, inverter, and point of interconnection.
- Equipment schedule: model numbers, ratings, listing, conductor sizes.
- Structural drawings and calculations: roof framing, attachment spacing, load path, flashing details.
- Utility interconnection application and approval conditions.
Worked example
A single-line shows a 200 A main breaker panel with a 200 A busbar and a 40 A backfed PV breaker at the opposite end. Under the 120% rule, the busbar allowance is 200 × 1.2 = 240 A; 200 A main + 40 A PV = 240 A, so it is exactly acceptable. If the plans called for a 50 A PV breaker, 250 A would exceed 240 A and the design would need a supply-side connection, a larger busbar, or a different panel. The inspector should verify the breaker location, not just the arithmetic.
Traps
- Reading only the single-line and missing roof setback dimensions.
- Confusing AC and DC ratings in the equipment schedule.
- Missing revision clouds and superseded sheets.
- Assuming a structural letter covers a changed attachment layout.
- Ignoring utility approval conditions on the plans.