Automobile assembly lines and other factory operations are massive, intricate undertakings. Each individual part must properly carry out its task to contribute to the entire system. More often than not, small and large mechanical processes are controlled by something called an electrical control panel. This blog will explain what electrical control panels are and the many components and make up the panel as a whole.
An electrical control panel could be thought of similar to the human body. Within the human body are the vital organs that control it. Similarly, an electrical control panel is a metal box that contains critical electrical devices that electrically control and monitor a mechanical process. The outer metal box is known as the enclosure. Enclosures are often made from aluminum or stainless steel and will vary in size depending on the size of the process. Electrical control panel enclosures can have multiple sections, each with its own access door.
There are three non-electrical components in an electrical control panel: the back panel, DIN rails, and wiring ducts. The back panel is a sheet of metal on the inside of the enclosure allowing users to drill mounting holes for other devices. This leads into the DIN rail, a metal rail used for mounting devices within an enclosure. Finally, the wiring duct allows operators to efficiently route wires in an organized manner while simultaneously reducing electrical noise between devices.
Now let’s look at the electrical components of a control panel. These are the main circuit breaker, surge arrester, transformer and 24-volt power supply, terminal block, programmable logic controller (PLC), relays and contactors, network switch, and the human machine interface (HMI).
Main Circuit Breaker
This part of the control panel serves as the source of power for all devices within the enclosure. The circuit breaker frequently features a disconnect on the outside of the panel, allowing operators to shut off the power.
Once power enters the panel via the main circuit breaker, it runs through a surge arrester. This is a device that protects the electrical equipment inside the control panel from electrical surges or overvoltages. Electrical surges can come from a variety of sources, ranging from a lightning strike to a utility power surge.
Transformer and 24-Volt Power Supply
The power supply is also commonly connected to a transformer that switches power down when necessary to power smaller devices. The 24-volt power supply serves a similar function. If incoming power is greater than 120 volts, the transformer is used. Once the power is at 120 volts, the 24-volt power supply can be used to take it down to 24 volts.
A terminal block comprises two terminals capable of joining two or more wires together. They can be arranged in conjunction with several other blocks and mounted on a DIN rail to run power from a single source to many different devices.
Programmable Logic Controller (PLC)
The PLC is essentially the brain of an electrical control panel, as it controls and monitors the entire mechanical process. The PLC features a central processing unit where the logic program is stored, as well as an array of inputs and outputs that control and monitor the assembly line. Devices including proximity switches, photo eyes, and other sensors are used on the assembly line to provide the PLC with the necessary feedback to control the operation of the line.
Relays and Contactors
The PLC’s outputs are wired to a bank of relays used to control an internal contact that sends power to turn a device on the assembly line on or off. Small relays can control devices such as lights or fans, but for larger components like motors, a bigger relay, known as a contactor, is used.
Near the PLC you will also find a network switch. This is a 24-volt device used to communicate to and from the PLC with network compatible devices along the assembly line.
Human Machine Interface (HMI)
An Human Machine Interface (HMI) is a user interface or dashboard that connects a person to a machine, system, or device, in this case the control panel. It can be mounted directly on the panel or in a remote panel located closer to the machinery. The PLC can send signals to the HMI for monitoring and the HMI can send signals to the PLC for controlling the machinery.
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