Topic 2 of 5
Drawings, scales and symbols
Drawings show what goes where. Reading them correctly saves fitting things in the wrong place.
Types of drawing
| Drawing | Shows |
|---|---|
| Location or site plan | Where the building sits on the site and its surroundings |
| Layout drawing (floor plan) | The positions of sockets, lights, switches and equipment in each room, using symbols |
| Block diagram | The main parts of a system and how they connect, as simple boxes |
| Circuit (schematic) diagram | How a circuit works electrically, without showing physical positions |
| Wiring diagram | How each conductor is actually connected between terminals |
| As-fitted (as-built) drawing | What was really installed, including any changes, for handover |
Symbols
Electrical drawings use standard graphic symbols from BS EN 60617, so anyone can read them. Each drawing has a key (legend) explaining the symbols used, and a title block with the drawing number, revision, scale and date.
Scale
A scale of 1:50 means 1 mm on the drawing is 50 mm in real life.
Real length = drawing length × scale
- At 1:50, 80 mm on the drawing is 80 × 50 = 4,000 mm, which is 4 m.
- At 1:100, 35 mm on the drawing is 35 × 100 = 3,500 mm, which is 3.5 m.
- To go the other way, divide: a 6 m wall at 1:50 is 6,000 ÷ 50 = 120 mm on the drawing.
Floor plans are usually 1:50 or 1:100. Site and location plans use smaller scales such as 1:500 or 1:1250.
Exam tip: always check you're using the latest revision of a drawing. Working from an old one is a common cause of mistakes.
Mini test
6 questions. Pick an answer to see if you're right and why.