December 2009

Enclosure-rated PLC ports

By Brandi S. Borgstadt

NFPA 70E is often referred to as the arc flash standard, and this electrical safety guideline allows for few exceptions when working on live voltage in and around enclosures. If voltage is present, then electrical incidents can happen, and the incidents only happen if voltage is present. Therefore, creating a barrier that keeps workers away from voltage, or an arc flash explosion, is a sure way to increase electrical safety around enclosures.

One approach proving to be the most effective is the notion of thru-door electrical safety.  While the concept may be self-explanatory, a basic definition is designing enclosures that take as many components as possible from inside the enclosure and put them on the outside of the cabinet. The most common instrument used in thru-door electrical safety is the programmable logic controller (PLC) port. Since keeping enclosure doors closed has become the key objective for any Safety Director who understands the benefits of enacting the NFPA 70E guidelines, finding ways to program and test equipment without opening the door is an essential component of compliance to NFPA 70E.  Having a variety of PLC ports to fit the many different types of enclosures is a fundamental key to unlocking all the benefits of a thru-door electrical safety program. The National Electrical Manufacturers Association (NEMA) prescribes number designations that indicate design characteristics of enclosures. There is an array of types of enclosure-rated PLC ports that vary depending on the degree of protection needed against things like corrosion, windblown dust and rain, splashing water, hose-directed water, falling dirt, dripping corrosive and non-corrosive liquids, and undamaged by the formation of ice on the enclosure. 

The most commonly used enclosure-rated PLC port is rated NEMA Type 12/4 because they are dust and water tight, but this was not always the case.  In the 1970s and 1980s, the most common enclosure was Type 13 because it provided protection against the spraying of oil. Oil-based coolant was the standard choice when cutting metal because of its ability to keep down temperatures.  However, due to growing concerns regarding the environmental effects of oil, the U.S. Environmental Protection Agency instituted stringent regulations regarding the disposal of oil-based products.  Many companies found the new regulations regarding oil-based coolants to be cost prohibitive, and they switched to water-based ones. The rise in popularity for enclosures rated to protect against water reflects that change. 

Other common enclosure-rated PLC ports include NEMA Type 1, which are used on flush mounted enclosure types that protect people from coming in contact with live wires.  Also, there are NEMA 4X rated PLC ports, which are similar to NEMA 12/4 enclosures with the exception that NEMA 4X enclosures are corrosion-resistant.

There are also enclosure-rated PLC ports to protect in locations categorized as Class 1 Groups C or D, as defined by the National Electric Code.  NEMA Type 7 enclosures are "designed to be capable of withstanding the pressures resulting from an internal explosion of specified gases, and contain such an explosion sufficiently that an explosive gas-air mixture existing in the atmosphere surrounding the enclosure will not be ignited." 

Finding the correctly-rated PLC port to enhance compliance to NFPA 70E guidelines is essential to any thru-door electrical safety program, yet protecting oneself and company from the direct and residual effects of an arc flash are not the only benefits to using PLC ports with enclosures. More companies are finding that using enclosure-rated PLC ports in their thru-door electrical safety program enhances not only their compliance to NFPA 70E, but it also increases employee productivity.  If an external PLC port is mounted on an enclosure, programming machines does not have to mean taking them down or offline. No longer will it be necessary to call in an electrician who has to don Personal Protective Equipment to open the panel door.  Neither will people and equipment be put unnecessarily at risk of an arc flash for a simple task like updating software or changing run times. Keeping panel doors closed means employees can do their jobs quicker and more efficiently outside the enclosure and away from voltage.  Enclosure-rated PLC ports that are custom made to fit a company's exact programming needs also means the cost-effectiveness is not limited to the time savings and arc flash protection. 

Often times, regulations brought forth from this governing board or that regulation committee are unfunded mandates.  These regulations are deemed necessary and become standards to which companies are legally and morally compelled to adhere. Yet, the cost and effort of implementing them is the sole burden of the company.  While no one is proposing companies should ignore the recommendations of these boards and committees, it is suggested thru-door safety methods that enhance compliance to NFPA 70E are not only safety-sound, but they can also be business-savvy decisions that have a positive effect on the balance sheet.

ABOUT THE AUTHOR

Brandi S. Borgstadt (brandib@grace-eng.com) is marketing manager for Grace Engineered Products, a leading innovator of thru-door electrical safety.