Classified-area control panels
Designing a control panel rated for a classified area can be a daunting task for individuals with limited or no prior experience. These four basic steps should get you started in the right direction:
1. Determine applicable codes for your geographic region—Before embarking on the design and laying out components, determine which governing agencies and applicable codes will come into play. That includes being cognizant of where the system will be built in addition to where it will be installed. If installed in another country you may have additional regulations to consider.
2. Obtain official documentation that declares the area classification—Note the emphasis on official, getting verification of the declared rating with tangible documentation. This is not an area in which “back of napkin,” or “word of mouth,” will suffice. A misstated classification requirement jotted down during a conference call could result in very serious if not deadly consequences.
3. Identify design constraints that may limit viable options—Knowing what capabilities can’t be supported can avoid going down dead ends. For example, don’t suggest a pressurized cabinet if instrument air isn’t available.
4. Don’t sacrifice functionality and safety as you weigh the pros and cons of viable solutions—Don’t forget that control panels in classified areas are typically very costly to produce and must be de-energized for maintenance, which results in downtime. The best solution is to move the system to a non-classified area and utilize intrinsic safety barriers. If relocation is not an option, then you must sift through the pros and cons of a pressurized (aka purged) enclosure versus an XP (explosion proof) enclosure to determine a path forward.
Although cost of ownership is always part of the equation, here I believe functionality will dictate much of the direction as it rightfully should. As an overview, XP enclosures are limited in size, are self-contained, and are capable of meeting some of the more difficult classifications. In contrast, pressurized systems can be fairly large, require additional support systems such as instrument air, and can only meet certain classifications. Less critical criterion to consider for both options are installation cost, installation methods, and accessibility.
This post was written by Andy Crossman. Andy is a senior control system specialist at MAVERICK Technologies, a leading automation solutions provider offering industrial automation, strategic manufacturing, and enterprise integration services for the process industries. MAVERICK delivers expertise and consulting in a wide variety of areas including industrial automation controls, distributed control systems, manufacturing execution systems, operational strategy, business process optimization and more.