Select Page

Understanding the general differences between UL 508A and UL 698A is the first step in meeting the standards for engineering control panels. But before determining the specific content addressed in UL 508A and UL 698A, it must be asked, “How is a control panel actually defined?”

According to UL 508A,
“This equipment consists of assemblies of two or more power circuit components, such as motor controllers, overload relays, fused disconnect switches, and circuit breakers, or control circuit components, such as pushbuttons, pilot lights, selector switches, timers, and control relays, or a combination of power and control circuit components, with associated wiring, and terminals. These components are mounted on, or contained within, an enclosure, or are mounted on a sub-panel.”*

In other words, your typical PLC panel or motor starter enclosure at a water or wastewater facility constitutes a control panel, and would fall under these standards.

With that said, it should be noted that based on that definition, there are some instances in which a panel would be exempt from UL 508A requirements. For example,

  • A field wiring interconnect panel solely containing terminal strips
  • An enclosure with only one electrical device
  • A fiber patch panel with no electrical circuitry

Certainly, there may be other safety considerations related to the aforementioned scenarios, but they fall outside of the jurisdiction of UL 508A.

Once the standards have been identified, and the enclosure is defined as being subject to them, it is simply a matter of determining how to design for the standards pertaining to the particular enclosure at hand. UL 508A defines standards pertaining to general practices (wiring, disconnects, overcurrent protection, control circuits, etc), while UL 698A defines standards pertaining to interfacing with hazardous locations (intrinsically-safe barriers, spacing, grounding, etc).

Because UL 698A solely describes the specifics of safety circuit extensions (and doesn’t cover general practices), any panel constructed to UL 698A standards must also meet UL 508A standards. In other words, it’s not either/or when it comes to panels containing safety circuits—UL 698A is essentially an “extension” to the standards contained within UL 508A. With that said, if there are conflicting requirements between the two standards, any requirements in UL 698A supersede those found in UL 508A.

Best practices begin with definitions, and control panel design is no different. Once you know the standard and have accurately defined the enclosure, you’re well on your way to a successful design.

*UL 508A Standard for Safety: Industrial Control Panels,” UL, July 31, 2017, 10