Control Panel Design: Tips and Tricks

Enclosure ratings, filters, input and output, networking, and safety are among enclosure design considerations.

04/24/2012


All control panel design activity must start with an awareness of the enclosures working environment. Follow the NEMA environmental rating for the area for all components in the panel. For example, in many food plants all external surfaces are coated daily with sanitizing foam producing airborne corrosives, and then rinsed with 80 lb force of hose-directed water. This requires NEMA 4x rated equipment for this area. Using a NEMA 12 enclosure, which provides some protection against water ingress from dripping or light splashing, would not meet the requirements of this area. Don’t mix and match components within an enclosure, in particular for externally mounted devices on the panel.

Where risk of arc flash exists, panels should be externally stickered, alerting workers of such risk. Requirements for working in such panels should include wearing appropriate personal protection equipment for the panel.

When dealing with pneumatic equipment in the panel, always exhaust the air outside the panel. A recommended practice is to put the pneumatic penetrations low in the panel. Moisture in pneumatic air is a common problem, so placing the entry low will insure there are no drips on electronic equipment, should moisture ever become a problem. It is also a good idea to use a low micron prefilter for biologics and some water, coupled with a coalescing filter, to remove the majority of water in the air.

From an equipment protection standpoint, wiring conduit penetrations should never be at the top of the panel. Moisture and water in conduit lines are not that uncommon. Penetrations near the bottom are the safest from an equipment protection standpoint but will be harder to work with for the electricians. Mid-level side-mount penetrations are a common compromise.

While not necessary, systems will be easier to maintain over time with true earth grounds versus floating grounds. This can help mitigate panel equipment damage in the event of inadvertent cross-connects between two different potential levels.

Input/out racks

A good practice is to segregate signal types. TriCore engineers group discrete I/O and analog I/O by voltage type. Always run analog signals in shielded cable. It is a good practice to minimize interference as combining different voltage types in internal panel wiring ducts. (Conflicting voltages should cross at right angles to minimize interference.)

Motor control panels

Motor starters and drives often have networked cable. Generally this should be isolated from high-voltage cable, unless using a high-voltage-rated Ethernet cable. It is a best practice to have a physical barrier within an enclosure for high- and low-voltage sections, although size and cost considerations often come into play. Touch-safe terminals should be used, with cover plates used for high-voltage power distribution.

- David McCarthy is president and chief executive officer, TriCore Inc. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering.

www.tricore.com

www.nema.org

http://controleng.com/integration



No comments
Consulting-Specifying Engineer's Product of the Year (POY) contest is the premier award for new products in the HVAC, fire, electrical, and...
Consulting-Specifying Engineer magazine is dedicated to encouraging and recognizing the most talented young individuals...
The MEP Giants program lists the top mechanical, electrical, plumbing, and fire protection engineering firms in the United States.
High-performance buildings; Building envelope and integration; Electrical, HVAC system integration; Smoke control systems; Using BAS for M&V
Pressure piping systems: Designing with ASME; Lab ventilation; Lighting controls; Reduce energy use with VFDs
Smoke control: Designing for proper ventilation; Smart Grid Standard 201P; Commissioning HVAC systems; Boilers and boiler systems
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Consulting-Specifying Engineer case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Protecting standby generators for mission critical facilities; Selecting energy-efficient transformers; Integrating power monitoring systems; Mitigating harmonics in electrical systems
Commissioning electrical systems in mission critical facilities; Anticipating the Smart Grid; Mitigating arc flash hazards in medium-voltage switchgear; Comparing generator sizing software
Integrating BAS, electrical systems; Electrical system flexibility; Hospital electrical distribution; Electrical system grounding
As brand protection manager for Eaton’s Electrical Sector, Tom Grace oversees counterfeit awareness...
Amara Rozgus is chief editor and content manager of Consulting-Specifier Engineer magazine.
IEEE power industry experts bring their combined experience in the electrical power industry...
Michael Heinsdorf, P.E., LEED AP, CDT is an Engineering Specification Writer at ARCOM MasterSpec.