When specifying a control enclosure there are a wide range of requirements that must be met from physical size and form factor to environmental ratings and thermal considerations.
Your PLC and control hardware will need a safe and secure home (Figure 1). The power distribution, safety system, contactors, relays, controllers and terminals need to be housed in the appropriate control enclosure and choosing one is not a simple task. There are many mechanical and control system requirements that must be met to get it right, and some of them are reviewed here.
It starts with a layout
On new designs, it is best to have a final or at least have preliminary electrical schematics and a parts list before specifying an enclosure. These documents help to create a panel layout drawing’s needed enclosure size. The layout should follow best practices by separating high-power and low-power components and the related electrical noise, along with grouping like components together and maintaining proper spacing between components for proper heat distribution.
Don't pack it all in a box; plan ahead, and future maintenance will be a better experience.
Where are you going to put it?
The location and function of the enclosure drive the design and form factor. There are many types of enclosures such as wall mount, free-standing, disconnect, rack, IT, consoles, operator interface, outdoor and hazardous location. There are also often requirements and specifications related to the enclosure placements depending on the application. Many configurations are available with a variety of names, so work carefully with the vendor regarding questions during specifying. Working with the mechanical designers or integration crew is also important, or the enclosure may not fit.
It's not uncommon to mount an enclosure on a wall between existing equipment. It is also often necessary to embed the enclosure in a machine frame, and the mechanical guys are not shy about giving the control enclosure as little room as possible. Reserve and confirm the space needed for the control system enclosure through proper design and reviews. Even details such as door clearance from the machine frame and surrounding equipment must be checked.
Safe and secure
Keeping the control hardware clean and dry is the primary function of the control enclosure, and much information is available online explaining NEMA and IP ratings. These ratings define the ability of the enclosure or related accessory to withstand harsh industrial environments. NEMA and IP ratings are similar in that both specify protection against ingress of solid foreign objects and liquids. NEMA also specifies protection against corrosive substances.
While IT enclosures may be installed in climate-controlled rooms where an open or NEMA 1 configuration is suitable, industrial environments are better suited for enclosures rated NEMA 12, 4 or 4X which are equivalent to IP54 and IP65 respectively with the NEMA 4X having protection from corrosion. Many options are available so understand the area classification, but don't skimp on the seal in industrial environments. Keep this in mind when specifying accessories for the enclosure such as a fan and bulkhead fittings, also.
Something as simple as a handle on a enclosure door can affect safety and protection of both personnel and hardware. Often, if door clamps are used, they are left loose allowing dust, oil and foreign materials to enter the enclosure. A variety of handles and latching mechanisms are available to allow quick access to the control panel but quickly seal the door shut.
Handles and disconnects with door interlocks and through-door disconnects also help to ensure personnel protection by providing lockout/tagout points and by inhibiting opening the door unless power is off.