 1300 So (in RRD it is increased to 1500 S2). 4. The design loop is the subscriber loop under study for a given distribution area to which the switch design limit is applied to determine conductor sizes (i.e., gauges or diameters). It is normally the longest loop in the cable of interest. 5.4 SUBSCRIBER LOOP DESIGN Table 5.4 Some Properties of Cable Conductors Mutual Attenuation Diameter Capacitance Resistance at 1000 Hz (nF/km) Loading (s2/km) (dB/km) 0.405 0.511 0.644 Source: ITT, Outside Plant, Telecommunication Planning Documents. (Courtesy of Alcatel.) (Ref. 4) 5. The theoretical design is the subscriber cable makeup consisting of the two finest (smallest in diameter) standard consecutive gauges necessary in the design loop to meet the switch design limit. There are three steps or procedures that are carried out before proceeding with resis- tance design: (1) determination of the resistance design boundary, (2) determination of the design loop, and (3) selection of the cable gauge(s) to meet design objectives. The resistance design boundary is applied in medium- and high-subscriber-density areas. LRD procedures are applied in areas of sparser density (e.g., rural areas). TRANSMISSION ASPECTS OF VOICE TELEPHONY The design loop length is based on local and forecast service requirements. The planned ultimate longest loop length for the project under consideration is the design loop, and the theoretical design and gauge(s) selection are based on it. The theoretical design is used to determine the wire gauge or combinations of gauges for any loop. If more than one gauge is required, Ref. 6 states that the most economical approach, neglecting existing plant, is the use of the two finest consecutive standard gauges that meet a particular switch design limit. The smaller of the two gauges is usually placed outward from the serving switch because it usually has a larger cross section of pairs. Since the design loop length has been determined, the resistance per kft (or km) for each gauge may be determined from Tables