When we configure and wire our control panel housings, we follow all the regulations to the letter. However, because our panels house a constantly increasing array of devices, we're faced with design uncertainties about issues, such as how much expansion space (mostly for I/O) to leave in the panel; the most efficient designs to minimize wiring; how to leave only the minimum device spacing and deal with device density and potential overheating; and how to avoid additional cooling requirements. Simply asked, who has some best practices they've learned and would share?
—from January'14 Control Design
A Lot to Consider
This is a complex question with no easy answer. When asked to design for future expansion, you need to understand the process being controlled, and if the process has no room or plans for expansion, then maybe no future space is required. The question of budget is also paramount when determining how much extra space and equipment can be included in the panel. A commonly specified spare space requirement is 20%, but most engineered drawings and panel layouts do not show this. Is it the panel builder's responsibility to correct this at bid time and possibly not capture the work against a panel builder who quoted to the drawings which do not show this spare space and equipment?
Make certain the wire duct is sized for some (about 25%) extra capacity, some of which may be used in the field for the base design I/O.
My rules of thumb are:
- Leave room near the power distribution sections for one additional power supply and several (20%) control fuses or circuit breakers with terminal blocks;
- Design cooling for 20 to 30% extra capacity, some of which is absorbed at the base design level due to dirty filters that often do not get attention;
- Side panels in some cases can be added to the interior left and right walls of the enclosure, and if you plan for this when designing the enclosure, it can often be a great benefit later. This requires the enclosure be deeper than specified, but if explained to the customer, it is easy to sell. A deeper enclosure also helps when future additions of HMIs or pushbuttons are done, thus reducing the risk of these devices bumping into back panel components;
If the panel I/O terminal block arrangement is not defined well, then careful planning can save considerable space. Some engineers want every channel fused for DI, DO, AI and AO, which can add up very fast. Perhaps group-fusing, dual-level or compact fuse/terminal blocks can be used.
—Ken Schultze, Engineering manager, Easter-Owens, www.easter-owens.com
Manage the Wires
Putting too much in one control panel can be costly if you introduce EMI noise, thermal problems or poor network connectivity. Up to half of the control panel space is consumed for wire management that is often inefficient. Optimize how DIN-rail modules and terminal blocks are deployed with wiring duct to reduce space required and provide design flexibility for device spacing and future expansion. A rapidly growing area that consumes significant panel real estate is Ethernet switch deployment. A new way to deploy Ethernet switches is to install separate, pre-wired, integrated zone enclosures with optimized spacing for these critical network connections. Panduit and Pentair Hoffman collaborated on a new website, www.hoffman-panduit.com, to share control panel best practices and learnings on topics including space optimization, noise mitigation, environmental protection (including thermal), security and safety.
—Dan McGrath, Industrial automation solutions manager, Panduit, www.panduit.com
Machine Mount Alternative
When configuring control panels to accommodate ever-changing I/O points, consider the worst case. But this might result in an oversized control panel, which is not cost-effective and could leave the customer asking why such a large cabinet. Our solution is to not put the I/O points in the control cabinet, but to use an on-machine solution, such as Allen-Bradley's 1738 ArmorPoint I/O. It can be mounted on the machine without a cabinet and close to the sensors and actuators. With connectivity support for DeviceNet, ControlNet, EtherNet/IP and Profibus, it can be used with a wide variety of PLCs.
—Joe Allard, Controls engineering, Pearson Packaging Systems, Software Aids
You should take a look at 3D virtual validation. By using some very simple but effective tools you can easily create, edit and visualize your complete enclosure in 3D before you decide to manufacture that enclosure.