Crowded Panels: Heated Discussion

We farm out most of our repeat-design panel building work, but we often do the specials ourselves. It's been getting more crowded in many of these panels. Sometimes the simplest and shortest wiring arrangement means more heat generation around the controller and other sensitive components than might be wise. Any tips, best practices or software tools to share for optimal placement of components?

—From July '11 Control Design

Answers

Best Practices

Your problem contains two main issues for which we have best practices to suggest. For the first, which is that it's getting more crowded in many of the panels, the best practice is simply to put it all in a bigger box. That might sound callous or overly simplistic, but when it comes to panel building, like building a race engine, there is no substitute for cubic inches. If that is not possible, try using a deeper box with the same footprint, and mount components in multiple tiers. One trick is to have multiple mounting panels, on swing-out hinges, kind of like the pages of a book.

Another trick is to use two mounting panels, back-to-back in the center of the enclosure, with access from both the front and the rear, which essentially doubles the amount of component mounting space. If you can't go deeper, can you go taller? Or wider? The bottom line is, if you are adding more components, you need a larger box or you need to use the space in the existing box more effectively and efficiently.

Other space-saving tricks: Use encapsulated transformers and mount outside the cabinet (this also removes unwanted heat from within the cabinet); or omit the disconnect switch—the UL508A standard does not require one.

Larger boxes also have added thermal benefits, which addresses the heat issue. As a best practice here, if it isn't wise, don't do it. Again, somewhat simplistic, but without knowing the full story, we must assume this is a UL508A-listed industrial control panel application. That is a 40 °C standard, meaning the air surrounding the components cannot exceed those temperature limits at any time during full-load, steady-state operation, regardless of what the temperature outside the enclosure is.

There are numerous ways to control temperature around sensitive components. Make sure to adhere to the spacing recommended by the component manufacturer. In addition to keeping the control panel away from heat-generating objects, you'll need to keep heat-sensitive components as far away as possible from heat-generating components within the panel. Keep heat-generating devices together to make it easier to manage the heat.

Mounting heat-sensitive components in the lower portion of the cabinet will help to keep them cooler because heat will naturally rise to the top of the panel. You can mount components on the side wall of a panel if necessary to gain maximum air space/air circulation between heat-sensitive and heat-producing components, or even mount heat-sensitive components in a separate, isolated cabinet. Conversely, you can mount the heat-producing components (transformers, line reactors, VFDs, etc.) external to the panel. Raising components and mounting rails up from the mounting panel with standoffs is relatively inexpensive, and greatly improves air movement.

Provide cabinet vents if possible. If not, provide an air conditioner or other heat-mitigating device. Perform a heat calculation to determine the additional cooling (vent grills, fans, A/C unit, heat exchanger, etc.) needed to maintain internal panel temperature to within the components' maximum operating temperature range.

If using additional cooling, position components so as to not impede air flow or as little as possible to achieve maximum cooling efficiency.

Kenneth Wilson, Sr. Application Development Engineer,
Son Dinh, Industrial Control Panel Application Engineer,
Schneider Electric, www.schneider-electric.com

Err on the Cool Side

We focus very little on the physical placement of components; instead, we focus heavily on obeying minimum clearance specifications from the various component manufacturers. We also do a heat rejection analysis on every panel we build. If necessary, we mitigate the heat load with fans, air conditioners or heat exchangers. All of the major enclosure manufacturers have graphs and software tools to predict temperature rise, and these same tools will offer equipment to remove that heat.

In the heat rejection calculation, we use the maximum ambient temperature for the installation, the sum total of the heat rejection for every component, and the materials of construction for the enclosure, with stainless steel being among the worst for heat rejection. We verify that the temperature rise plus the maximum ambient temperature doesn't approach or exceed the maximum rating for the lowest-rated electrical component. If it does, we provide cooling. This analysis is quick, straightforward and easy to do. Important to remember: Electronics are happiest when they're cool, so err in that direction if the situation is marginal.

Jack Chopper, Chief Electrical Engineer,
Filamatic, www.filamatic.com

Power = Heat

Because enclosures can often be space-constrained and thermally challenging, there are a couple tips that we offer to our OEM and machine builder customers. First, we suggest that Power over Ethernet (PoE) should be considered. PoE offers power and data over the same Ethernet cable, eliminating the need for a power supply inside the enclosure as well as any related cabling. So you can reduce the amount of space you need and decrease the amount of heat produced. We see an increasing number of industrial devices coming online with PoE as manufacturers and end users are realizing significant benefits associated with this technology.