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ARTICLE 525 Carnivals, Circuses, Fairs, and Similar Events
These locations (carnivals, circuses, fairs, and similar events) are similar to assembly occupancies [Article 518], but there's a big difference. The assemblies occupancies covered by Article 518 aren't temporary. Another big difference is that the items covered by Article 525 include such things as amusement rides and attractions.
See if you can spot other similarities, as well as differences, between Article 518 and Article 525 as you study. Being aware of these will help you understand both articles better.
ARTICLE 547 Agricultural Buildings
Two factors have a tremendous influence on the lifespan of agricultural equipment: dust and moisture.
Dust gets into mechanisms and causes premature wear. But with electricity on the scene, dust adds two other dangers: fire and explosion. Dust from hay, grain and fertilizer is highly flammable. Litter materials, such as straw, are also highly flammable. The excrement from farm animals may cause corrosive vapors that eat at mechanical equipment but can also cause electrical equipment to fail. For these reasons, Article 547 includes requirements for dealing with dust and corrosion.
Another factor to consider in agricultural buildings is moisture, which causes corrosion. Water is present for many reasons, including wash down. Thus, Article 547 has requirements for dealing with wet and damp environments. Article 547 also includes other requirements. For example, it requires you to install equipotential stray voltage planes in all concrete floor confinement areas of livestock buildings containing metallic equipment accessible to animals and likely to become energized.
Livestock animals have a very low tolerance to small levels of stray electrical current, which can cause loss of milk production and, at times, livestock fatality. As a result, the NEC contains specific requirements for an equipotential stray voltage plane for buildings that house livestock.
ARTICLE 551 Recreational Vehicles and Recreational Vehicle Parks
Article 551 is similar to Article 550. After all, RVs are similar to mobile homes. While mobile homes are essentially trailers, RVs are essentially vehicles. Thus, RVs have their own article. RVs also have voltage converters, which mobile homes do not have. Other differences emerge as you look more closely.
While most of the requirements in Parts II and III apply to the RV manufacturer, an electrician doing work in an RV must also comply with these requirements.
If you're going to install an engine generator for an RV, you'll need to understand Part IV. Parts V and VI are primarily for RV manufacturers.
The typical electrician starts to get involved in Article 551 with Part VII, which provides the requirements for power distribution systems in RV parks. Perhaps the most important aspect of Part VII is understanding how to calculate loads and apply the demand factor, based on the number of RV sites in the park.
ARTICLE 555 Marinas and Boatyards
Water level isn't constant. As the earth and the moon play their eons-old game of tug-of- war, oceans, lakes, rivers, and other bodies of water rise and fall at the shoreline. Other forces also cause the water level to change. For example, lakes and rivers vary in depth in response to rain. The variations can sometimes be dramatic.
To provide power to a marina or boatyard, you must allow for the variations in height between the point of use and the power source. Article 555 addresses this issue.
But that's not the only issue involved with marinas and boatyards. As you might expect, Article 555 also presents requirements for accommodating the high levels of moisture inherent in these installations. Boatyard and marina installations pose further challenges as well. For example, sunlight reflected off the water is much more intense than it would otherwise be-and this has implications for insulation. Other factors to consider include temperature extremes, increased abrasion, oil, gasoline, diesel fuel, ozone, acids, and chemicals.
Then, of course, docking a boat isn't as easy as pulling into a shopping center parking spot with your automobile. Electrical equipment must meet certain spatial requirements, such as not interfering with mooring lines or masts.
Article 555 begins with the concept of the electrical datum plane. You might think of it as the border of a "demilitarized zone" for electrical equipment. Or you can think of it as a line that marks the beginning of a "no man's land" where you simply don't place electrical equipment. Once you determine where this plane is, don't locate transformers, connections, or receptacles below that line.
ARTICLE 590 Temporary Installations
It's a common misconception that temporary wiring meets a lower standard than that of other wiring. In truth, it merely meets a different standard. The same rules of workmanship, ampacity, and circuit protection apply to temporary installations as to other installations.
So how is a temporary installation different? In one sense, it does meet a lower standard. For example, you can use Types NM and NMC rather than the normally required raceway-enclosed wiring-without height limitation. And you do not have to put splices in boxes.
You must remove a temporary installation upon completion of the purpose for which it was installed. If the temporary installation is for holiday displays, it cannot last more than 90 days.
Article 590 addresses practicality and execution issues inherent in temporary installations, thereby making the installation less time consuming to install.
Mike Holt's Comment: If you desire more information about any of the above changes, be sure to order my Changes book and/or library (Video/DVD).
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