U.S. building design conventionally moves through Schematic Design (SD) → Design Development (DD) → Construction Documents (CD), following the AIA's standard phase structure. What "complete" actually means for the electrical scope at each stage is easy to underestimate — electrical deliverables mature at a different pace, and in a different shape, than architectural ones do.
Schematic Design: sizing the service, not yet designing the system
At SD, electrical scope is less about specific equipment and more about space and capacity claims that constrain the architecture: how much room the main electrical room and switchgear need, roughly where the service entrance and main distribution risers have to sit, and a preliminary service size based on rough-order-of-magnitude load estimates rather than a final calculation. This is the phase where an undersized electrical room or riser shaft gets baked into the building's floor plan and vertical circulation in a way that's expensive to correct later — SD electrical input is disproportionately about protecting future flexibility, not producing numbers a contractor could build from.
Design Development: the one-line gets real
DD is where a preliminary single-line diagram becomes an actual one-line diagram with real equipment selections — a specific switchgear line, specific panel and transformer sizes — rather than a generic capacity placeholder. Load calculations mature from SD's planning-grade estimate toward the full NEC Article 220 calculation, and conduit and cable tray routing gets laid out, not just sized. DD drawings still generally aren't permit-ready; they're the coordination set used to resolve conflicts — a cable tray run crossing a beam, a panel location blocking a door swing — before committing to final construction documents.
Construction Documents: the set that gets permitted, bid, and built
CD is the complete package: full plans, panel schedules, one-line and riser diagrams, and specifications — the version of the design that goes to the AHJ for permitting and to contractors for pricing. Everything behind a proper NEC load calculation, voltage drop check, and fault current study is aimed at producing CD-quality, permit-ready numbers — a level of rigor SD and DD deliberately don't require yet, because committing to that detail before the building's basic configuration is settled means redoing the calculation every time the architectural plan shifts.
Why electrical BIM coordination matters most at DD
DD is where cable tray, conduit, and equipment space claims collide most directly with structure and with the other trades competing for the same ceiling cavity. This is the phase where 3D coordination — clash detection between conduit, cable tray, and structure in Revit or Navisworks — delivers the most value, because DD-level routing is detailed enough to reveal real conflicts but not yet so finalized that resolving them means redrawing a completed CD set.
Delegated design is a real variation, not just a contract label
Not every project has the engineer of record producing every electrical detail. Design-build delivery and delegated design — where a specialty contractor produces final engineering for a defined system, such as fire alarm or certain low-voltage scope — shift detailed design later into the schedule, often into construction as a deferred submittal. A design team working under one of these models needs to be explicit, in the contract documents, about exactly which systems are delegated and what performance criteria the delegated design has to meet. An ambiguous delegation is a common source of coordination failure, precisely because it isn't caught at DD the way a fully engineer-of-record-designed system's conflicts would be.
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Electrical Design