. Electric railway journal . the extension of the local electric rail-way system. Extensions of about 54 miles are proposedfor the next four years. 248 Electric Railway Journal Vol. 52, No. 6 Hard Spots in Trolley Wire Resultfrom Hammering of Trolley Wheels Flexibility of Supports and Light-Weight FittingsWill Reduce Hammering and Result inIncreased Service By G. H. Bolus Designing Engineer The Ohio Brass Company TROLLEY wire freely suspended between supportsassumes a catenary curve the depth of which isgoverned by the weight of the wire, the tension towhich it is subjected and the distance be
. Electric railway journal . the extension of the local electric rail-way system. Extensions of about 54 miles are proposedfor the next four years. 248 Electric Railway Journal Vol. 52, No. 6 Hard Spots in Trolley Wire Resultfrom Hammering of Trolley Wheels Flexibility of Supports and Light-Weight FittingsWill Reduce Hammering and Result inIncreased Service By G. H. Bolus Designing Engineer The Ohio Brass Company TROLLEY wire freely suspended between supportsassumes a catenary curve the depth of which isgoverned by the weight of the wire, the tension towhich it is subjected and the distance between a trolley wire could be suspended between supportswithout sag the ideal condition would be catenary type of construction with messenger wireand hangers of various lengths approximates this, buteven with a spacing as short as 10 ft. between hangersthere is some sag in the trolley wire. The catenary type of construction is not well adaptedto city service as the extra number of fittings required. REDUCED SECTION OP TROLLEY WIRE COMMON AT EARAPPROACHES and the cost are against it. The most common con-struction for this service consists of direct suspendedtrolley wire supported by brackets or cross-span wiresevery 100 ft. With such a spacing of the supports thereis more or less sag. For instance, at 1800-lb. tensiona No. 00 copper trolley wire sags in. When a trolley car equipped with pole and wheelhaving, say 25-lb. tension, is run under a stretch ofdirect suspended trolley wire the wheel moves in botha horizontal and vertical direction, the latter due to thesag in the wire. In other words, the trolley wheeltravels a greater distance than the car. An abruptchange in direction of motion occurs at support points,which causes a hammering or hollowing out of thetrolley wire by the force of the blow. In practice the points where hollowings occur in thecontact wire are usually spoken of as hard spots in theline and they are present at all supports an
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