Understanding Basic Electrical Ladder Diagrams

For those of us who work with and design electrical systems, we understand the inherent complexity behind circuitry. To simplify complex systems, engineers use ladder diagrams which provide a graphical representation of the electric schematic for circuits. Electrical ladder diagrams provide a way for personnel to gain a better understanding of electric pathways when troubleshooting, evaluating and maintaining any circuit.

Understanding and interpreting the symbols used in creating ladder diagrams is essential for being able to effectively read a diagram. Ladder diagrams are composed of rectangles, lines and other common electrical symbols. In order to quickly diagnose or repair an electrical circuit, you must be familiar with the meanings of these symbols in order to determine what is going on within the system.

Circuit Power Sources

At the top of most electrical ladder diagrams is the power source, typically of alternating current (AC). It is often shown as a circle symbol. The symbol will have one or more lines extending from it that represent the incoming power. This can be derived from a transformer, part of the control system, or even a unique power source like a battery.

Overload Protection

In any motor-driven equipment, it is important to include overload protection. This allows the motor to draw more current than normal but protects it from overheating or excess current. The circuit should be designed to protect itself and the user from any harm. This is usually accomplished with a fuse, circuit breaker, or relay. They may also include circuit monitors that can detect any changes in current.

Contacts, Switches, and Relays

Contacts, switches, and relays are used in a number of different ways. On electrical ladder diagrams, contacts, switches, and relays are usually represented by a box with one or two lines coming out of it. Contacts can be normally open (NO) or normally closed (NC). Switches are shown as a manual switch, while relays are often represented by a coil and contact points.

Control Systems

The heart of any ladder diagram is the control system. This contains the components used to program and control the operation of the motor or machine. It is represented by a block diagram, a large rectangle that includes all the parts of the system along with arrows indicating the flow of information. The arrows may also indicate where a signal is gained, lost, or combined.

Conclusion

Ladder diagrams are a great way to quickly and easily understand complex electrical circuits. With some basic knowledge and understanding of the symbols used in ladder diagrams, it is easier to diagnose, troubleshoot and repair any electrical system. Knowing the components, symbols and different parts of a ladder diagrams, will help you safely and efficiently work with any electrical system.

Plc Ladder Diagrams For Electrical Engineers