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Industrial Control Panel Design Guide

2019-08-16223

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Industrial control panels consist of power circuits or control circuits (or both) which provide signals that direct the performance of machinery or equipment. Industrial control panels don’t include the main power, nor do they include the controlled equipment; rather, the panel is mounted on a back panel (or subpanel) or in an enclosure, depending on the application. Industrial control panel design begins with weighing design requirements and specifications and preparing schematics, but the design process can be quite complex in order to ensure that all applicable regulatory standards and safety requirements are met.

This guide provides an overview of the key design considerations applicable to industrial control panel design, including schematics, relevant regulatory standards, and design considerations relating to every facet of effective control panel design for industrial equipment and machinery.

Industrial control panel design–Schematics

Control panel design for industrial equipment and machinery is an important undertaking, resulting in an interface designed to control a machine or process. It’s not a simple matter of selecting an appropriate enclosure and a back panel that houses the electrical hardware. So, the proper hardware must be mounted on a back panel and properly wired and integrated into the machine – any improper configuration can result in malfunctioning machinery, but it’s also likely to pose an unnecessary risk to operators.

The process should always begin with an evaluation of the specifications, requirements, and regulatory standards. After these considerations are evaluated, drawings are created to outline the specific configuration of wiring, circuits, controls, and every other aspect of the final control panel. Good design addresses both the electrical and physical requirements. These drawings should include:

1.Functional diagram
2.I/O (Input/Output) diagram
3.Power distribution
4.Control cabinet and back panel layouts
5.Bill of materials

Because there are so many elements in a proper schematic, a table of contents is also recommended. The schematic is the foundation for the subsequent development of an industrial control panel.

Regulatory standards related to industrial control panel design

Despite many Code cycles, many industrial control panels are still not compliant with the regulatory standards which are accepted industry-wide. Compliance, however, is critical for ensuring minimal safety risks associated with installing and operating industrial equipment and machinery.

Design considerations for Industrial control panels

A variety of design considerations must be weighed throughout the design process in order to design a control panel that meets functional requirements, application specifications, and regulatory standards. The following design decisions represent the primary design considerations in developing an industrial control panel, although additional considerations specific to individual applications may apply.

Enclosures and space requirements

The intended environment largely dictates the appropriate type of enclosure for an industrial control panel. You'll need enough space to install and wire components, and it's also wise to plan for several receptacles to reduce the need for extension cords when it's necessary to power test equipment or appliances.

Placement is another consideration related to enclosures. Depending on where the panel will be located, you may need to account for swing requirements of cabinet doors (if a cabinet enclosure is being used). If a control panel will be located in an area with a high ambient temperature, a ventilation fan or air conditioning may be required to keep the control panel within an ideal operating temperature range. If temperature control applies, it's necessary to allow for easy access to air intakes and exhaust vents (which makes it easier to access and replace filters).

Space considerations are paramount, as one of the most common violations involves control panels that are too small or too confined to allow for the proper space for wiring and wire bending. It's also wise to consider space requirements not only for the current configuration but possible future needs, as restricted space is a common challenge for retrofits.

Wire sizing and component types

When it comes to wire sizing and selecting the appropriate component types, there are two important rules of thumb:

1.Wires should be sized based on load  current. In turn, circuit protection should be based on wire size. Selecting the appropriate wire size is essential for ensuring that the circuit is capable of delivering the required load  current, while selecting the best circuit protection reduces the risk of  fire by preventing wires from overheating.

2.Component types should be selected based on functional requirements. Selecting components of the right size is critical, as well, as voltage and load current requirements can mandate minimum size requirements. Components must be capable of handling the voltage and load current requirements reliably, but they also must function as required.

Control components and circuits

What type of controls are appropriate for the application? There are a variety of options from relays to timers to terminal blocks. Opt for the simplest control components possible.

Control circuits provide logic for the operation of power circuit components. These circuits are typically lower-voltage for safety, and components such as control power transformers (CPTs) and power supplies are utilized to convert the power circuit voltage to the control circuit voltage.

Supply conductors

Supply conductors should allow for the highest possible load that may occur. This is typically calculated by determining the sum of all connected motors and apparatus (keeping in mind duty cycles and which motors and apparatus will operate simultaneously), and adding this sum to the full load current for all resistive loads plus 125% of the full load current of the highest rated motor.

Handling overcurrent protection

You'll also need to consider overcurrent protection in the design phase. There are two options: overcurrent protection can be placed ahead of the panel or incorporating a single, primary protective device in the panel itself. Depending on the application, it may not be desirable to integrate the protective device in the panel to minimize the need to open an enclosure.

Operator devices

Operator devices include components such as push buttons, indicator lights, digital panel meters, levers, and the like, but these devices can also be more complex, touch-screen displays. Such HMIs (human-machine interfaces) allow for more complex functionality, but also require computing components and software development, which can add to the cost.

When it comes to controls, the old K.I.S.S. principle (Keep It Simple, Stupid) applies. Simpler is always better, but simpler may not always be possible. You should, however, opt for the simplest operator devices appropriate for the functional requirements to support ease of use.

All industrial control panels should include an emergency stop (which differs from a cycle stop), typically a self-latching control in a mushroom or palm type.  they must be a push-button design which is hard-wired into the safety circuit. Additionally, any start buttons or switches should be located directly above or to the immediate left of the associated stop button.

Labeling

It's imperative to properly label all wires, terminals, and other components in an industrial control panel. It's a time-saving strategy that also reduces the likelihood of errors in testing, routine maintenance, and repairs. Labels should be durable enough to withstand the conditions of the target environment to avoid fading and damage that renders them unreadable.

Front panels and faceplates

Front panels and faceplates may seem like an afterthought, but these elements are equally as important to the overall operation of machinery as the interior functional components. Front panels should be durable enough to withstand extreme temperatures, weather conditions, cleaning products, and chemicals to protect the underlying components.

Front panels and faceplates may include metal or plastic substrates, depending on the application specifications, and can be mounted with studs, adhesives, or fasteners. Digital or screen-printed graphics provide visual guidance for operators and incorporate labeling of operator devices to ensure usability. Therefore, face plates must have the durability necessary to remain readable for the life of the asset.

There are many, many individual components and elements that go into an industrial control panel. This guide is meant to provide an overview of the primary design considerations.

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