Digital telephones line engineering Page 299 of 504Telephones and Consoles Description, Installation, and OperationSelecting a LoopFor a Meridian digital telephone, the loop must be without bridge taps, lessthan 175 ohm DC resistance, and less than 12.0 dB loss at 256 kHz. Forsingle-gauge 22 and 24 AWG cable, and D inside wiring, the length limit is914.4 m (3000 ft). For single-gauge 26 AWG cable, the length limit is640.08 m (2100 ft).The allowable loop length assumes there is no under-carpet cable. If there isunder-carpet cable that is a different type than Western Electric (WE) 4-paircable, reduce the allowable loop length by using the following equation:LM = [12 – (UC x UL)] /LLwhere:Calculating DC Loop ResistanceUse Procedure 46 to calculate the DC loop resistance.Procedure 46Calculating DC loop resistance1 Calculate the DC loop resistance by adding the resistance of each cablesection. Calculate the resistance of each cable section by using thefollowing formula (cable resistances are given in Table 41 on page 300):LRi = CRi x SLiwhere:LRi = DC resistance for cable section iCRi = conductor resistance per unit length for the cable section iSLi = length of cable section iLM = loop length limit in km (kft) (excluding the length of theunder-carpet cable)LL = loop loss in dB/km (dB/kft) at 256 kHzUC = length of the under-carpet cable in km (kft)UL = loss of the under-carpet cable in dB/km (dB/kft) at 256 kHz(see Table 43 on page 306 for dB values)
