Remember, in estimating the size of your plant for light, heat, and power, that it does not have to be big enough to use all the devices at one time. Also remember, that two water horsepower to one electrical horsepower is a very liberal allowance; and that a generator working under one-half or two-thirds capacity at normal loads will require less attention than a machine constantly being worked above its capacity. Therefore, let your generator be of liberal size, because the difference in cost between a 5 and 10 kilowatt machine is not in proportion to their capacity. In fact (especially among second-hand machines), the difference in cost is very small. The mere fact that the generator is of 110 electrical horsepower capacity does not require a turbine of 20 horsepower. The chances are that (unless you wish to heat your house and do large power jobs) you will not use more than 3 to 5 electrical horsepower normally; therefore an allowance of 10 water horsepower, in this case, would be ample. A plant used simply for lighting the house and barn, for irons, and toasters, and one horsepower motors, need not exceed 2 or 2-1/2 kilowatts for the generator, and 5 or 6 horsepower for the turbine wheel. Normally it would not use one-half this capacity. CHAPTER VII TRANSMISSION LINES Copper wire--Setting of poles--Loss of power in transmission--Ohm's Law and examples of how it is used in figuring size of wire--Copper-wire tables--Examples of transmission lines--When to use high voltages--Over-compounding a dynamo to overcome transmission loss. Having determined on the location of the farm water-power electric plant, and its capacity, in terms of electricity, there remains the wiring, for the transmission line, and the house and barn. For transmission lines, copper wire covered with waterproof braid--the so-called weatherproof wire of the trade--is used. Under no circumstances should a wire smaller than No. 8, B. & S. gauge be used for this purpose, as it would not be strong enough mechanically. The poles should be of chestnut or cedar, 25 feet long, and set four feet in the ground. Where it is necessary to follow highways, they should be set on the fence line; and in crossing public highways, the ordinance of your own town must guide you. Some towns prescribe a height of 19 feet above the road, others 27 feet, some 30. Direct current, such as is advised for farm installations, under ordinary circumstances, does not affect telephone wires, and therefore transmission lines may be strung on telephone poles. Poles are set at an average distance of 8 rods; they are set inclined outward on corners. Sometimes it is necessary to brace them with guy wires or wooden braces. Glass insulators are used to fasten the wires to the cross-arms of the poles, and the tie-wires used for this purpose must be the same size as the main wire and carry the same insulation. _Size of Wire for Transmission_