Standards are everything when it comes to control systems engineering. Whether it’s high-performance practices for HMI development, iterative quality control for PLC programming, or peer-review design for industrial process control, enforcing standards is a critical aspect of any legitimate engineering endeavor, including control panel design.
Underwriter’s Laboratory (UL) serves as one of the best certification organizations for ensuring control panel safety. The two primary governing standards for panels designed for the water and wastewater industry are UL 508A (Standard for Safety of Industrial Control Panels) and UL 698A (Standard for Safety of Industrial Control Panels Relating to Hazardous (Classified) Locations). Identifying the purposes of each, and the differences between the two, is critical for ensuring that control panel designs adequately meet these standards.
According to UL, standard 508A covers “industrial control panel enclosures and industrial control panels for general use, as well as specific use panels for industrial machinery, air conditioning and refrigeration, crane control, elevator control, flame control, marine use and use as service equipment.” This standard addresses safety practices for the average control panel located in a non-hazardous area (for example, an electrical room at a water treatment facility).
On the other hand, standard 698A covers industrial control panels that are “intended for installation in ordinary locations with intrinsically safe circuit extensions into Class I, II, and III, Division 1 and 2; and Class I, Zone 0, 1 and 2 hazardous (classified) locations.” This standard addresses safety practices for the average control panel that interfaces with instrumentation in a hazardous area (for example, a wetwell transducer in a lift station connected to a PLC in an above-ground enclosure).
While UL 698A addresses panels related to hazardous locations; it does not address panels installed in hazardous locations. Other standards (such as UL 1203, UL 60079, UL 1604, and NFPA 496) pertain to those situations.
The distinctions can be summarized as follows:
- A control panel installed in a non-hazardous location, without any circuit extension into hazardous locations, would be expected to meet only UL 508A standards.
- A control panel installed in a non-hazardous location, with circuit extensions into hazardous locations, would be expected to meet UL 508A and 698A standards.
- A control panel installed in a hazardous location would be expected to meet other, more stringent, standards.
Ultimately, a standard is only as good as it is upheld. Thus, identifying which standard meets the need is foundational to best practice for design. After all, standards are everything.