. Electrical world. hase star, or delta, or com-bined star and delta give generally a slightly lower maximum volt-age on the conditions shown above. It is now- necessary to consider the conditions to be met by ground-ing the low-potential distributing mains, an illustration of future reference, is given in Fig. 4. All low-potential circuits requiring over 660 watts should bewired and operated on the three-wire system, unless the load con-sists of one receptive device requiring over this amount of power,in which event it should be operated wherever possible from theouter wires of the
. Electrical world. hase star, or delta, or com-bined star and delta give generally a slightly lower maximum volt-age on the conditions shown above. It is now- necessary to consider the conditions to be met by ground-ing the low-potential distributing mains, an illustration of future reference, is given in Fig. 4. All low-potential circuits requiring over 660 watts should bewired and operated on the three-wire system, unless the load con-sists of one receptive device requiring over this amount of power,in which event it should be operated wherever possible from theouter wires of the system, thereby preserving the balance and re-quiring considerably less weight of conductors. The two-wiresystem, besides requiring an excessive investment for conductors,does not readily permit of grounding, owing to the grounded legcarrying the same amount of current as the other wire. In a properly balanced three-wire system the neutral wire carriesonly a small percentage of the total current. By placing the per-. FIC. 4.—DMGRAM OF GROUNDED CONNECTIONS. manent ground on this neutral, should it accidentally open, theground connections would not be called upon to carry any largeamount of power; consequently, they need not be made as heavyor with as much care as would be necessary for their operation on atwo-wire system. A grounded direct-current, two-wire system might, under certainconditions, result in severe electrolytic action upon other metallic 354 ELECTRICAL WORLD and ENGINEER. Vol. XLIII, No. 8. structures in its vicinity. This would not be true of a three-wiresystem, as the neutral current would be of small amount, and inmost cases of an alternating character, reversing at each change ofthe unbalanced load. Referring to Fig. 4, we will assume that ground connection i ismade by a driven pipe or small plate buried in moist earth, theresistance of which under even the most favorable conditions willseldom be less than 50 ohms. With wire b (Fig. 4) grounded, across betwee
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
