How to Read Electric Schematic Drawings

Schematic drawings show how the components of an electrical device are interconnected.

Schematic drawings, also called wiring diagrams or schematic diagrams, are maps that show how the components of an electrical device are connected. The maps are mostly lines representing wires, which connect together an array of individual symbols made from lines. The symbols stand for electrical components such as switches, lights, coils and capacitors. The symbols must be learned one at a time. Schematic diagrams are essential for troubleshooting, debugging and building electrical devices.

Instructions

Understand the Map

1. Learn the symbols associated with your power supply -- the source of electricity for your device. There are two standard sources: wall plugs and batteries. The symbol for a wall plug is a line drawing of a wall plug -- a semicircle with two parallel lines running through it and extending out the flat side of the semicircle to suggest the two prongs of the plug. The symbol for a battery is a series of alternating lines perpendicular to the line that connects the battery to the rest of the device. The alternating parallel lines are alternating short and shorter.

2. Understand how the symbols for switches are denoted as breaks in the wire, with a short line nearby that looks like it could be pushed into place to make the wire continuous. Such switches are called "normally open." Sometimes it looks like the short line is already in place, and these switches are called "normally closed." A switch that switches from one circuit to another will look like a short line that is attached to one wire, but could be moved to connect to two or more other wires. A push button switch will be a short line parallel to the gap. The ground symbol is a wire that terminates in four or five parallel lines that get progressively shorter.

3. Get a list of the symbols of the electric components that are specific electrical components you will be using. House wiring symbols tend to be squares or circles with the device name and part number written beside the symbol. Typical audio and automotive symbols tend to be the resistor, which has a zigzag in the line, the capacitor, which has a gap with a short perpendicular line on either side, and the coil, which has several loops in the line. Transistors, used in both audio and computer circuits, are the conjunctions of three lines. One line terminates in a short line, and the other two lines terminate on the other side of the short line and one of these two lines will have an arrowhead.

Tips & Warnings

• A schematic diagram is more like a subway map than a road map in that the length of the lines do not correspond to the length of the wires. Schematic diagrams show what is connected to what, not what the distances are.

• The components are not arranged in the schematic as they are in the device. The schematic is laid out to look good on the page. The actual components are laid out using other constraints.

References

• Physics: Schematic Diagrams
• ThinkQuest: Schematic Diagrams
• PlayHooky: Using Schematic Diagrams

Resources

• PhysicsClassroom: Circuit Connections