The terms schematic drawing and P&ID drawing are sometimes used interchangeably but they refer to different things. Understanding the distinction matters when specifying drawing requirements for a project or when briefing a CAD outsourcing supplier.

What is a schematic drawing?

A schematic drawing is a simplified diagram that shows the components of a system and how they are connected, without representing their physical size, shape, or layout. Schematics are used to convey system logic and connectivity rather than physical arrangement.

Schematic drawings are used across a wide range of disciplines. In electrical engineering, schematics show circuits, wiring, and connections. In mechanical and HVAC engineering, schematics show pipework flow and system connections. In fire engineering, schematics show alarm zones and panel connections.

What is a P&ID drawing?

A P&ID is a specific type of schematic used in process engineering. It follows strict international standards — ISA 5.1 and BS EN ISO 10628 — and shows all pipework, valves, instruments, and control systems in a process plant.

The key distinction is that a P&ID is a formalised, standardised document with specific symbol conventions and data content requirements. A schematic drawing is a broader term covering any simplified diagram showing system connectivity.

When would you use a schematic vs a P&ID?

Use a schematic drawing for electrical wiring diagrams, fire alarm system schematics, HVAC flow diagrams, plumbing schematics, and general system connectivity diagrams for M&E installations.

Use a P&ID for process plant documentation in oil and gas, utilities, chemical processing, pharmaceuticals, and any facility involving instrumented process systems with control loops.

Outsource CAD services

Outsource CAD produces both schematic drawings and P&ID drawings across all engineering disciplines. Contact us for a free quote.