MEANING OF TERMS

Evening Post, Volume CVI, Issue 105, 31 October 1923, Page 12

MEANING OF TERMS

USED IN ELECTRICITY ■SIMPLE EXPLANATIONS. ■ In writing of electricity, one has to use perforce certain terms—such as volt, unit, kilowatt, amperes, horse-power— . which the .general public does not always ■.understand quite clearly. Electricity is different from most o£ the other forms of energy in that it is invisible, noiseless in itself and odourless. It issues no warnings of its presence and its potency, and : that is one of its dangers to the careless public. There is. no difference in appearance between a, live wire and a dead one, and an escape of electricity does not announce itself to the nose like an escape of .gas to the eye like a, leak :of water. To the general public electricity remains a mysterious power, '• however simple it is in use. Some explanation of terms used is therefore desirable. .HORSE-POWER, The unit of mechanical power is called the horse-power, curiously enough from James Watt's estimate of the work that a_ horse could do. Watt .wanted to sell his steam engine for pumping and other .purposes, for which horses had .briginalIy been used, and he had to make a, case for the engine on some unit of power basis. Naturally, he selected the horse, which he found to be capable on the average of doing 25,000 foot-pounds of i work per minute, a foot-pound being .weight multiplied by feet lifted,- and, to Ibe on the safe side, he added 50 per [ cent._ to this and made his unit of mechanical power a horse-power of 33,000 foot-pcrunds per minute. This remains the unit of mechanical power to-day. ELECTEIGAL TERMS. When electricity came into use new terms had to be devised to express measurements of its various aspects. Thus, electricity really requires quite a dictionary to itself. For the .following explanation of terms,.the writer^ indebted to the Manawatu Power Board's booklet :— VOLT is the unit of pressure, which may be compared to- water in a pipe at a pressure of so many pounds to the square inch. AMPERE is the unit rate of the 1 volume of the flow of current, like so many gallons per second of water alon<* a pipe. OHM is the name given to the unit of resistance in a conductor or wire. The three units of measurement, each called after a notable pioneer in electricity, are so related that if a pressure of one volt is -connected to a conductor of one ohm resistance. a current of one ampere will How. WATT is the name used to denote the product of volts and amperes. Thus, electric current of amperes at 250 volts represents 1000 watts or us it usually written a killowatt. A UNIT is 1000 watts used for one hour or a kilowatt for one hour, the kilowatt being made up of any combination of volts am} amperes, as explained. A horse-power is equal to 746 wattsor .746 kilowatt; conversely a kilowatt, is equal to 1.34 llorse-po'wer. But when the electrical energy measured on the meter corner to bi: re-convert-ed into mechuuiuul energy there is .ji certain loss ia. !t£s pjotfie,

1' horse-power and upwards—must be operated on 400 volts.

But 400 volts is too high a voltage to use in a lamp; 230 volts is now one of the world standard voltages, so another \yir» is brought out of the transformers called the "neutral" wire. Thus , it will be noted that all the high voltage lines (3300 and 11,000 and 110,000 volts) are of three wires; all the consumers lmes from the distributing side of transformers ■ carry the current on four wires (400 and 230 volts). ■ There are technical advantages to this ir-ethod that need not be gone into hero, but amongst other advantages may' be mentioned that if a person touches-a live wire, the shock is of only 230 volts, as the neutral wire is rounded (that is, fastened to a pipe driven in the ground).. Another is that the power is transmitted at 400 volts in most rv-ses, and used at 0n1y.230 volts, making great economy in the size of wire.