490 ELEMENTS OF ELECTRICAL ENGINEERING. 



If the customer uses his lamps 2 hours per day the year round, 

 find the size of wires he should use in his house, in circular mils 

 per ampere, for greatest economy, the cost of copper being 16 

 cents per pound, and the interest and depreciation being 8 per 

 cent. Ans. 4,507 circular mils per ampere. 



162. The cost of power at the switch-board in an arc-lighting 

 station is 2 cents per kilowatt-hour. The plant supplies a current 

 of 6.6 amperes to a circuit of 50 arc lamps which are operated 

 on a moonlight schedule for 2,160 hours each year. The cost 

 of copper is 21 cents per pound, and the annual charge on the 

 cost of the wire is 1 1 per cent, (interest 6 per cent., depreciation 

 3.5 per cent, and taxes 1.5 per cent). The cost of the wire is 

 high and its depreciation is large because the wire is insulated. 

 The price of 21 cents per pound is on the net weight of copper 

 in the wire and this price is intended to cover the cost of the 

 insulation. Find the size of wire to give a balance between loss 

 of power and cost of copper. Ans. 17,040 circular mils. 



Note. The falling of an arc light wire into the street would be very dangerous on 

 account of the high voltage. Therefore, it is important that an arc-lamp circuit be 

 very substantial. It is usually not considered allowable for this reason, to use wire 

 smaller than No. 6 Brown and Sharpe gauge (26,000 circular mils) for an arc-lamp 

 circuit. 



163. Find the cost to the station owners of 16.5 kilowatts of 

 power delivered for 1,200 hours each year at 220 volts over a 

 special line to a single customer at a distance of one mile from the 

 station, the wire being of such size as to give a balance between 

 loss of power and cost of copper. Determine the size of wire on 

 the basis of a 6 per cent, annual charge on the cost of the copper at 

 1 6 cents per pound, the cost of power at the switch-board being 

 2.5 cents per kilowatt- hour. Reckon the total cost of the line 

 at 2.25 times the cost of the copper, and reckon the total annual 

 cost of interest, depreciation, taxes, and maintenance of line at 

 15 per cent, of the total cost of the line. Ans. $1,176.80 per 

 year, or about 6 cents per kilowatt-hour delivered. 



164. Given ten groups of lamps, each group taking 10 amperes, 



