Relation to UL
The control panel—known in English as an “industrial control panel”—must meet various requirements depending on its location, purpose, and environment in order to be connected to the power grid in the United States. The easiest way to verify that regulatory requirements and standards have been met is through a UL label.
What is an industrial control panel?
Industrial Control Panel, abbreviated as IPC, refers to industrial switchgear or industrial control panels. The National Electrical Code (NEC) defines an IPC as an assembly of two or more components within an electrical circuit, a control circuit, or a combination of both. The rated voltage is 600 volts or less.
Regulatory Requirements
In North America, there are specific regulatory requirements and standards for industrial control panels. For example, ICPs must comply with the provisions of NEC Article 409.2 and Section 110.3(B), as well asANSI/NFPA 70. An ICP that does not meet these requirements and lacks certification will not be approved by the local AHJs (Authorities Having Jurisdiction). And that can be costly for the manufacturer. In addition to regulatory requirements, there are standards that apply to ICPs. These include UL 508A for the U.S. and CSA C22.2 No. 14 for Canada.
UL Program for Industrial Control Panels
In North America , Underwriters Laboratories (UL) is the world’s leading provider of testing and certification services. The organization offers an Industrial Control Panel Shop Program (ICP Program) that enables control panel manufacturers to custom-build ICPs or produce them in series. If control panel manufacturers have completed a specific certification process, they are authorized to affix the UL marks to the control panels themselves for the U.S. and Canada. They effectively become the certification body themselves. However, in Germany, there are only about a handful of companies that hold this authorization.
Industrial Control Panel – Certification Requirements
When regulatory agencies, designers, and certifiers of end products see the UL Mark, they can be confident that the ICP meets the certification requirements. The ICP program simplifies the process of obtaining UL certification while offering great flexibility in panel design. If the goal is to implement a UL-compliant system, it is important that as many of the components used as possible are already UL-listed and thus certified.
Industrial control panels for the Canadian market can also obtain UL certification, as UL and the Canadian Standards Association (CSA), Canada’s leading testing and certification organization, have entered into a formal agreement that allows for the approval of certain components for use in end products, including ICPs. Conversely, ICPCs for the U.S. market can also receive CSA certification. UL and CSA have introduced the following marks for these markets:
If the manufacturer does not participate in UL’s Panelshop program, it must have its ICPs certified by an external body. This involves a significantly greater investment of time and money.
Industrial Control Panel – Design
Planning an ICP should begin with a list of specifications, requirements, and regulatory standards. Based on this, drawings are then created to outline the specific configuration of the wiring, circuits, controls, and other details. This wiring diagram then serves as the basis for the development of the control cabinet.
There are a number of design considerations that should be incorporated into the design process:
- Enclosures and Space Requirements
The environment largely determines the appropriate enclosure type for the ICP. The enclosureof acontrol panel must meet certain requirements depending on the environment. - Wire Sizing
Wires should be sized based on the load current. Circuit protection, in turn, should be based on the wire size. Furthermore, the wire size must ensure that the circuit can supply the required load current, while the circuit protection must be selected to reduce the risk of fire by preventing the wires from overheating. - Component Types
In addition to functional requirements, selecting the correct size is also important when choosing components, as voltage and load current requirements may necessitate a minimum size.Furthermore, UL standards describe specific wiring requirements, such as wiring materials, conductor marking, circuit conductor sizing, and wire sizing. - Control Components
When selecting control elements—from relays and timers to terminal blocks—you should choose components that are as simple as possible.
Circuits Control circuits specify how the components of the electrical circuit are to operate. For safety reasons, these circuits typically operate at a lower voltage. Components such as control power transformers (CPTs) and power supplies are used to convert the circuit’s voltage to the control circuit’s voltage.
Supply Line Since varying loads may occur, the supply lines must be selected to accommodate the highest possible load.
Overcurrent Protection Overcurrent protection must also be taken into account as early as the design phase. It can either be placed outside the control cabinet or integrated into the control cabinet itself as a single, primary protective device. Depending on the application, it may be important to minimize the number of times the enclosure is opened. In such cases, the protective device should be placed outside the control cabinet.
Control DevicesControl devices range from pushbuttons, indicator lights, digital displays, and levers to complex touchscreen displays. The more complex these HMIs (human-machine interfaces) are, the more functions they have; at the same time, however, they also require more computer components and additional software. Control devices should be simple and user-friendly, while always ensuring that they meet all functional requirements.All ICPs should be equipped with an emergency stop switch featuring a self-locking mechanism. For this purpose, it has proven effective to install a red, momentary-action stop button with an elongated head—such as a mushroom-shaped one—to interrupt the machine’s power supply. These emergency stop switches are also required by the U.S. Occupational Safety and Health Administration ( OSHA ).- Labeling
All wires and terminals, as well as all other components in the control cabinet, must be properly labeled to reduce the likelihood of errors during testing, routine maintenance, and repairs. When using labels, ensure that they remain legible at all times and do not fade or become damaged in their intended environment.
General Questions About UL/CSA
What Are UL-Listed Industrial Control Panels?
For UL listing, representative samples of the industrial control panel are tested. If they meet UL’s applicable safety requirements during testing, they are awarded the “UL Listed” mark. The UL standards UL 508A (OrdLoc), UL 698A, or UL 1203 (HazLoc) apply to UL control panel construction.
Are all industrial control panels UL-certified?
The majority of industrial control panels are not certified as a whole, but consist of UL-listed components assembled in accordance with UL standards. It is crucial that all IPCs comply with the required safety standards when they are inspected on-site by inspectors from the AHJ (Authority Having Jurisdiction), the authorities responsible for ensuring compliance with local safety requirements.
Why does my industrial control panel need to be UL-listed?
The reason lies in safety considerations: The IPC must meet certain minimum electrical safety requirements. In North America, there are strict standards and regulations for this, such as UL 508A. If the industrial control panel or its components comply with the prescribed standard, it receives the UL Listed mark and is accepted by the on-site inspector without further testing. Without the UL Listed mark, there is a significant risk that the inspector will discover defects or deviations from the standard, that the control panel will not be approved, and that it therefore cannot be put into operation.
What is a UL 508A control panel?
UL 508A is the standard for Industrial Control Panels (IPC) that are exported to North America and used in all environments except hazardous locations. If the IPC and all its components comply with this standard, it receives the “UL Listed” mark upon UL certification. This mark is recognized by inspectors from the local authorities having jurisdiction (AHJ). The industrial control panels can be put into service without further detailed testing.
Zusammenfassung
The enclosure for industrial switchgear is referred to as an Industrial Control Panel Enclosure. Like control cabinets, these enclosures must also comply with the NEC and UL 508A, but they are not tested for compatibility with electrical components. They provide protection for a wide variety of electrical devices, such as circuit breakers or control panels. The UL Type Rating according to UL 50E is used to evaluate enclosures; enclosure types are classified there. Depending on the application (and location), the enclosure must meet specific requirements. For example, sufficient space for the individual components and their proper placement must be ensured. Incorrect sizing of industrial control panel enclosures is actually one of the most common NEC violations related to switchgear.
