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Facility Ground-System Design:Grounding Signal Cables and Analyzing Noise Currents.

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Grounding Signal Cables Proper ground-system installation is the key to minimizing noise currents on signal-carrying cables. Audio, video, and data lines are often subject to ac power noise currents and RFI. The longer the cable run, the more susceptible it is to disturbances. Unless care is taken in the layout and installation of such cables, unac- ceptable performance of the overall system can result. Analyzing Noise Currents Figure 20.32 shows a basic source and load connection. No grounds are present, and both the source and the load float. This is the optimum condition for equipment interconnection. Either the source or the load can be tied to ground with no problems, provided only one ground connection exists. Unbalanced sys- tems are created when each piece of equipment has one of its connections tied to ground, as shown in Figure 20.33. This con- dition occurs if the source and load equipment have unbalanced (single-ended) inputs and outputs. This type of equipment uti- liz...
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Units Conversion Table.

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Reference Data and Tables

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Safety and Protection Systems:OSHA Safety Requirements.

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OSHA Safety Requirements The federal government has taken a number of steps to help improve safety within the workplace. OSHA, for example, helps industries to monitor and correct safety practices. The agency's records show that electrical standards are among the most frequently violated of all safety standards. Table 24.9 lists 16 of the most common electrical violations, which include these areas: • Protective covers • Identification and marking • Extension cords • Grounding Protective Covers Exposure of live conductors is a common safety violation. All potentially dangerous electric conductors should be covered with protective panels. The danger is that someone can come into contact with the exposed, current-carrying conductors. It also is possible for metallic objects such as ladders, cable, or tools to contact a hazardous voltage, creating a life-threatening condition. Open panels also present a fire hazard. Identification and Marking Properly identify and label all...
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Safety and Protection Systems:Polychlorinated Biphenyls

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Polychlorinated Biphenyls P olychlo r inate d biphenyls (PCBs) belong to a family of organic compounds known as chlorinated hydro- carbons . Virtually all PCBs in existence today have been synthetically manufactured. PCBs are of a heavy, oil-like consistency and have a high boiling point, a high degree of chemical stability, low flammability, and low electrical conductivity. These characteristics led to the past widespread use of PCBs in high-volt- age capacitors and transformers. Commercial products containing PCBs were distributed widely from 1957 to 1977 under several trade names, including: • Aroclor • Pyroclor • Sanotherm • Pyranol • Askarel Askarel also is a generic name used for nonflammable dielectric fluids containing PCBs. Table 24.4 lists some common trade names for Askarel. These trade names typically are listed on the nameplate of a PCB transformer or capacitor. Health Risk PCBs are harmful because, once they are released into the environment, they tend not to br...
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Safety and Protection Systems:Facility Safety Equipment.

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Introduction Safety is critically important to engineering personnel who work around powered hardware, especially if they work under considerable time pressures. Safety is not something to be taken lightly. Life safety systems are those designed to protect life and property. Such systems include emergency lighting, fire alarms, smoke exhaust and ventilating fans, and site security. Facility Safety Equipment Personnel safety is the responsibility of the facility manager. Proper life safety procedures and equipment must be installed. Safety-related hardware includes the following: • E mergency power off (EPO) button. EPO pushbuttons are required by safety code for various types of facilities, including data processing (DP) centers. One must be located at each principal exit from the room. Other EPO buttons may be located near operator workstations. The EPO system, intended only for emergencies, disconnects all power to the room, except for lighting. • Smoke detector. Two basic type...
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