STATION WIRING 631 



insulation in time. In multiple-conductor cables this action does 

 not occur, the static activity being neutralized. 



Single-conductor cables are made in sizes up to 2,000,000 C.M. 

 and three-conductor cables up to 500,000 C.M. 



General Practice. The following is a general summary of 

 prevailing practice covering the kind of conductors and the manner 

 in which they are installed in a station. 



Bare Grounded Conductors. Bars, tubing, cable, wire: Used 

 for all kinds of ground connections or ground return circuits. 



Rare Conductors on Insulators. Bars, tubing, wire: Generally 

 employed for circuits above 13,200 volts. 



Insulated Conductors on Insulators. Wire, cable, rods: Used 

 for all circuits up to 13,200 volts when not housed in compartments 

 or conduits. 



Insulated Conductors in Iron Conduit. Cable: Employed 

 for voltages up to 1200 volts generally for small-capacity circuits 

 where size of conduit does not exceed 2 inches. 



Insulated Conductors in Clay or Fiber Ducts. Cable : May be 

 used for large capacity circuits for voltages up to 13,000 provided 

 ducts are maintained free from moisture. 



Leaded Conductors in Ducts or Conduits. Cable: Used for 

 voltages up to 13,200 when ducts or conduits are subject to mois- 

 ture. 



For convenience of reference, station wiring may also be classi- 

 fied as follows: 



1. Exciter and field wiring. 



2. A.C. generator and low-tension transformer wiring. 



3. Control and instrument wiring. 



4. High-tension wiring. 



Exciter and Field Wiring. These leads consist, as a rule, 

 of single-conductor rubber-covered cables with a double weather- 

 proof braid (or tape and braid), although for sizes larger than No. 

 0000 B. & S. the insulation may be varnished cambric. Because 

 of the inductive discharge in field circuits, causing an excessive rise 

 in potential when opening the circuit, it is important that a liberal 

 margin of safety is allowed in the insulation. For damp locations 

 lead-covered cables may be required. These leads are mostly 

 installed in iron conduits. 



Generator and Transformer Wiring. For this wiring varnished 

 cambric insulation is, as previously stated, preferable, the thick- 



