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By Mike Holt
CHAPTER 6 - SPECIAL EQUIPMENT
Chapter 6, which covers special equipment, is the second of four chapters that deal with special topics. Chapters 5, 7 and 8 deal with special occupancies, special conditions, and communications systems, respectively. Remember, the first four Chapters of the NEC are sequential and form a foundation for each of the subsequent four Chapters.
What exactly is "special equipment?" It is equipment that, by nature of its use, construction, or unique nature creates a need for additional measures to ensure the "safeguarding of people and property" mission of the NEC put forth in Article 90.
The NEC groups these logically, as you might expect. Here are the general groupings:
It's important to remember that Chapter 6 covers only the minimum safety requirements for the special equipment it covers and that, in most cases, other standards also apply. The NEC is not meant as a substitute for those other standards. So before you begin work on any of this special equipment, first obtain the standards written for that equipment. If you are not sure what standards apply, contact the manufacturer for assistance.
Article 600. Signs
One of the first things you will notice when entering a strip mall is that there is a sign for every store. Every commercial occupancy needs a form of identification, and the standard method is the electric sign. Thus, 600.5 requires a sign outlet for the entrance of each tenant location. Article 600 requires a disconnect within the line of sight of a sign unless the disconnect can be locked in the open position. The lamps in signs burn out for a variety of reasons, and tenants or owners change the lamps. But the signs themselves also change-tenants relocate all the time.
Another requirement is height. Freestanding signs, such as those that might be erected in a parking lot, must be located at least 14 feet above areas accessible to vehicles unless they're protected from physical damage.
As you studied Chapters 1 through 4, you saw requirements based on the laws of physics. A major theme in those chapters is how to prevent wires from melting. But, the physics approach is not the only one the NEC takes to safety. From bird droppings to bus traffic to bulb burnouts, you'll find Article 600 requirements compensate for the realities of commercial establishments.
Article 604. Manufactured Wiring Systems and Article 605. Office Furnishings (Wired Partitions)
The next two Articles are very similar. Article 604 applies to field-installed manufactured wiring systems, while Article 605 applies to relocatable partitions. In both cases, you are installing and/or assembling pre-wired components or subassemblies. These normally come with manufacturer's instructions, so Code compliance is almost automatic if you follow the instructions. However, you still need to:
The Articles contain the specific requirements. They aren't difficult to understand, but you should be familiar with them before installing manufactured wiring systems or wired partitions.
Article 620. Elevators, Dumbwaiters, Escalators, Moving Walks and Stairway Chair Lifts
With the exception of dumbwaiters, the equipment covered by Article 620 moves people. Thus, a major concept in Article 620 is that of keeping people separate from electrical power. That's why, for example, 620.3 requires live parts to be enclosed. For related reasons, HVAC circuits cannot exceed 600V.
Article 620 consists of the following Parts:
That's a quick overview, but it covers quite a bit. Now let's look at the requirements you really need to understand.
Article 625 Electric Vehicle Charging Systems
Two particular goals dominate Article 625:
Avoidance of inadvertent connections or disconnections. Vehicle charging connectors must be configured such that they aren't interchangeable with other electrical systems. They must prevent inadvertent contact of live parts with people. They must prevent unintentional disconnection. In fact, Article 525 requires automatic de-energization of charging cables under certain conditions. And, as you might expect, the grounding pole (if provided) must be the first to make and the last to break contact.
Provision of adequate ventilation. Batteries are chemical reaction chambers. As the chemicals in battery cells react, they release gases, such as hydrogen. Different types of batteries release different amounts of gas and some don't release much at all. But the types of batteries required for electric vehicles release relatively high amounts of gas. Thus, Article 525 devotes extensive space to ventilation requirements. Even when a charging station is outdoors, Article 525 provides height requirements to prevent ignition of battery gases.
If you keep these two goals in mind, you will better understand Article 525 requirements. Article 525 accomplishes other goals as well, but these two are responsible for the bulk of the text.
Article 630. Electric Welders
Welding equipment does its job either by creating an electric arc between two surfaces or by heating a rod that melts from overcurrent. Either way results in a hefty momentary current draw. Welding machines come in many shapes and sizes. On the smaller end of the scale are portable welding units used for manual welding, such as in a fabrication shop. At the larger end of the scale are robotic welding machines the size of a house, used for making everything from automobile bodies to refrigerator panels. All of these must comply with Article 630.
The primary concern of Article 630 is adequately sizing the conductors and circuit protection to handle this type of load. Fortunately for the power distribution engineer and the field electrician, Article 630 requires certain information to be provided on the nameplate of the equipment. Article 630 explains how to use this information for proper sizing of conductors and circuit protection.
Welding cable has requirements other conductors don't have. For example, it must be supported at not less than 6-inch intervals. Also, the insulation on these cables must be flame-retardant.
Article 640. Audio Signal Processing, Amplification and Reproduction Equipment
If you understand three major goals of Article 640, you will better be able to understand and apply the requirements. These three goals are:
In addition, Article 640 distinguishes between permanent and temporary audio installations. Part II provides requirements for permanent installations, and Part III provides requirements for temporary installations.
Article 645. Information Technology Equipment
One of the striking things about Article 645 is the requirement of a shutoff switch readily accessible from the exit doors (645.10). This requirement would seem to be wrong on its face because it allows someone to shut off the IT room from a single point. So despite having a UPS and taking every precaution against a power outage, the IT system is still vulnerable to a shutdown from a switch located outside the room. What was the Code making panel thinking of when they added this requirement?
They were thinking of fire and rescue teams. Having a means to shut down the power and disconnect the batteries before entering the IT room during a fire allows the rescue team to use fire hoses and other equipment without risking contact with energized equipment. Yes, there is loss of IT function during the shutdown. But if the room needs fire and rescue teams, loss of the IT function is the least of its problems at that time. The shutdown allows the rescue of people and property. A breakaway lock can protect the IT room from inadvertent shutdown via this switch.
What about the rest of Article 645? The major goal is to reduce the spread of fire and smoke. The raised floors common in IT rooms pose special additional challenges to achieving this goal, so Article 645 devotes a fair percentage of its text to raised floor requirements. Fire-resistant walls, separate HVAC systems, and other requirements further help achieve this goal.
Article 647. Sensitive Electronic Equipment
Power quality problems have caused misoperation of electronic equipment in some cases and outright loss in others. Attempts to protect this equipment from power quality problems have often taken approaches that endanger people and property. For example, a designer might consider the grounding system to be a source of dirty power and specify that the equipment not be connected to ground or that it have a floating ground. Article 647 provides some direction for designers and installers to resolve power quality issues without creating a dangerous situation.
Some people have criticized the title of Article 647, arguing that all electronic equipment is sensitive. The intent of that title is to convey the idea that Article 647 will apply to electronic equipment that the designer, installer, or user considers in need of extra protection from power quality issues. If the title simply said "electronic equipment," then it would imply a much broader coverage than what was intended.
People often refer to the voltage drop "requirement" in 310.15, 210.19 and 215.2. That is actually a Fine Print Note (FPN) that suggests voltage drop limits. However, the voltage drop specification in 647.4(D) is a requirement. And it's twice as stringent as the suggestion in the FPNs. However, it applies only to sensitive electronic equipment.
Pay attention to the grounding and labeling requirements of this Article. Most electronic equipment misoperations due to power quality problems cease occurring when an installation is brought into compliance with Article 647. Even more will clear up when the installation is brought into compliance with Chapter 3 wiring methods.
Article 680. Swimming Pools, Fountains and Similar Installations
The overriding concern of Article 680 is to keep people and electricity separated. Some ways Article 680 accomplishes this include:
After presenting general requirements in Part I, Article 680 covers specific equipment in subsequent Parts: permanently installed pools, storable pools, spas and hot tubs, fountains and pools and tubs for therapeutic use.
Article 690. Solar Photovoltaic Systems
A solar power system seems pretty simple at first glance. Solar panels produce electricity, which you use to supply power to a building. In the typical application, solar systems complement, rather that replace, one or more power sources. Additionally, solar power must provide some sort of energy storage (usually batteries) to be effective. Both of these factors complicate the picture. When you have another source, you must prevent backfeeds to the solar cells.
Even a standalone system needs an inverter to allow running normal equipment from the batteries. And whether the system is stand-alone complementary, you still need to meet requirements for grounding, overcurrent protection, labeling, and disconnecting means. Plus, the charging systems pose additional challenges to ensuring a safe installation. Article 690 addresses all of these issues.
Article 692 Fuel Cell Systems
Intro already exists in book. -Mark Lamendola
Article 695 Fire Pumps
The general philosophy behind Code Articles is that circuit protection will shut down equipment before letting the supply conductors melt from overload. Article 695 departs from this philosophy. The idea is that the fire pump motor must run, no matter what. It supplies water to a facility's fire protection piping. This piping normally supplies water to the sprinkler system and fire hoses. Article 695 contains many requirements to keep that supply of water uninterrupted.
Some of these requirements are intuitively obvious. For example, locating the pump so as to minimize its exposure to fire. Or, ensuring the fire pump and its jockey pumps have a reliable source of power. And, of course, it makes sense to keep fire pump wiring independent of all other wiring.
Other requirements seem wrong at first glance, until you remember why that fire pump is there in the first place. For example, the disconnect must be lockable in the closed position. You would normally expect these to be lockable in the open position because other Articles require that for safety of maintenance personnel. But the fire pump runs to ensure the safety of an entire facility and everyone in it. For this reason, fire pump power circuits cannot have automatic protection against overloads.
Remember, the fire pump must be kept in service, even if doing so damages pump. It is better to run the pump until its windings melt, than to save the pump and lose the facility. And the intent of Article 695 is to save the facility.
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