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API RP 552:1994(2007) pdf download

API RP 552:1994(2007) pdf download.Transmission Systems.
If groups of cubic trays arc stacked vcrtically, the signal wiring should he in the top tray, and high-voltage feeders should be in the bottom-most tray. With this arrangement. the signal wiring is not in the electric field that exists between all voltage lines and ground
The circuits, might be arranged top to bottom as follows:
a, Signal wiring.
b. Light-capacity power circuits.
c. Medium voltage AC and DC feeders.
d. High-voltage feeders.
Although direct routing is desirable for all types of wiring. the sensitivity of signal wiring to electrical magnetic interferences may call for special routing precautions. Magnetic field interference occurs when signal wires pass through strong AC fields which are present near large motors, generators, electric furnaces, and transformers. As a general rule. a minimum of 5 feet (1.5 meters) of clearance should be allowed between the noise generating equipment and signal carrying wires. If steel conduit is used, clearances can be reduced by half.
Signal leads should, if possible. enter or exit AC power equipment at right angles to the equipment’s magnetic field. When power and signal wiring cross in close proximity to each other, the crossover should be made at right angles and no closer than 12 inches (0.3 meters).
10 Effect of Transmission Distance on
Electronic Signal Installations
The design of an installation is largely governed by economics: for example. more expensive signal mLIItipIcxiflg equipment using fewer wires or fiber optic systems may be justified for long distances, hut less expensive direct connected wiring may be more economical for short distances. The economics of various types of transmission systems should be evaluated on an individual project basis.
The length of the transmission line also affects the magnitude of electrical inierferences. Generally, the longer the distance the greater the possibility of noise. Lightning also creates problems in longer lengths of cable. The spare conductors in a multiconductor cable should be grounded at one point so that they do not induce large voltage surges on signal circuits when lightning strikes nearby.
AC powered solenoid valves connected to wire runs of 10(X) feet (3000 meters) or more may fail to switch on the opening of the control contacts due to electrostatic
11 High Temperature Areas
When wire is run next to fired heaters or other heat radiating equipment (as occasionally is required with thermocouples), every effort should be made to keep the wire in areas where temperatures are not excessive. If this condition is not practical, wire with a moisture resistant, high temperature insulation should be used. A common junction box should be provided in a safe area, away from the heat source. to allow connection to regular wire which can be run the remaining distance.
12 General Information On Installation Methods For Electronic Systems
Although signal wires may be installed and protected from physical damage by methods that are similar to those for power wiring, such methods are not always sufficient for good signal transmission. Information on methods and hardware that result in a good signal transmission system is given in Sections 13 through 20. Routing of redundant data highway cables requires consideration of the need to maintain redundancy by avoiding exposure to common hazards.
13 Installation Of Trays For Electronic Systems
Cable trays may be used advantageously to support a large number of cables between two points if their use is permitted by the NEC and other applicable codes for the application in question. Tray use is generally limited to Division 2 and non- classified areas unless Intrinsically Safe wiring is used. The primary advantage of trays over conduit is their lower initial cost. Power Limited Tray Cable (PLTC) is normally required.
The diflerent types of trays are discussed in the following
13.2.1 Applications and LImitations
Many varieties of metal trays are available for either horizontal or vertical mounting. Prefabricated trays are usually purchased. hut some users prefer to have trays made in their own shops or by local steel fabricators, The general types of prefabricated trays for horizontal mounting are ladder. trough. and channel. A ladder tray is a prefabricated metal structure consisting of two longitudinal side rails connected by individual transverse members (rungs).


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