STATION WIRING 625 



insulators on telephone circuit in case of crosses with 

 power lines after series fuses are blown. 

 4. Drainage coils installed with fuses at each end of 

 line; possibly an additional coil at the middle if 

 the voltage to ground is not held to a safe value 

 by two coils. 



10. STATION WIRING 



Experience has shown that in a great number of instances 

 the shut-down of power plants has been caused by a defective 

 installation of the station wiring. The design and construction 

 of the cabling and wiring system of a station is, however, of equal 

 importance to the rest of the equipment. 



It is obvious that the main electrical conductors should be of 

 such a character and so installed as to minimize as far as possible 

 any trouble from short-circuits or grounds, and particularly to 

 confine such disturbances, in event of its occurrence, to the cir- 

 cuit affected. It is likewise apparent that such buses or circuits 

 on which a short would mean a complete station interruption 

 should be still better insulated and protected. 



The general practice of not providing automatic protection 

 on the excitation system makes it essential to properly install 

 all the exciter field circuits and to provide sufficient insulation to 

 care for the high inductive voltage inherent to field circuits. The 

 safety of the instrument and control system wiring should further- 

 more not be neglected, because in the event of trouble the main 

 circuits may become involved through the accidental operation 

 of an oil switch or the failure of a switch to open on an outside 

 short-circuit. Every cable and wire should, therefore, have a 

 definite place provided for it in advance, just as much as any 

 other piece of machinery, and wires carrying currents of different 

 voltages should, as far as possible, be kept apart from each other. 



Insulation. The principal materials used for cable insulation 

 are: rubber compound, saturated paper, and varnished cambric. 

 Rubber insulation is commonly used on low-voltage cables of 

 small size say up to 600 volts and No. 0000 B. & S. For larger 

 sizes and higher voltages, either paper or varnished cambric in- 

 sulation may be used. The latter is very much less hydroscopic 

 than paper insulation. In fact, while not offered as being water- 

 proof in itself without 'a lead sheath, it is nevertheless sufficiently 



