Basic Electricity I History of Electricity Ancient Greeks – Static Electricity • Rub amber with wool. • Amber becomes negatively charged by attracting negative charges (electrons) from the wool. • The wool becomes positively charged. • The amber can then pick up a feather. How? • The Greeks called amber Elektron, Which is where we get the term electricity. Benjamin Franklin (1706 – 1790) • Conducted many experiments on static electricity from 1746 – 1751 (including his lightning experiment) and became famous throughout Europe by describing these experiments in a series of letters to Peter Collinson. Alessandro Volta (1745 – 1827) • Interpreted Galvani’s experiment with decapitated frogs as involving the generation of current flowing through the moist flesh of the frog’s leg between two dissimilar metals. • Argued with Galvani that the frog was unnecessary. • In 1799 he developed the first battery (voltaic pile) that generated current from the chemical reaction of zinc and copper discs separated from each other with cardboard discs soaked in a salt solution. • The energy in joules required to move a charge of one coulomb through an element is 1 volt. Other Notable Electrical Pioneers • Andre Ampere- 1 coulomb/sec moving past a point is called an Ampere(I) • Michael Faraday- Wrote Law about electromagnetism. • Joseph Henry- worked with Inductance, measurement of inductance are Henrys(L) • Heinrich Hertz- worked with electromagnetic waves. Measurement of frequency is in Hertz(Hz) • Georg Ohm- discovered a relationship between Voltage(E), Amperes(I), and resistance(Ω). Ohm’s Law defines this relationship. Notable Electric Inventors Thomas Edison 1847 - 1931 • Invented and developed complete DC electric generation and distribution system for city lighting systems • Carried on a major competition with George Westinghouse who developed an AC generation and distribution system Notable Electric Inventors Nikola Tesla 1856 - 1943 Over 700 patents Rotating magnetic field principle Polyphase alternatingcurrent system Inducton motor AC power transmission Tesla coil transformer Radio Fluorescent lights War of the Currents • Edison had developed a system that ran on Direct Current (DC), and was convinced that this system would be used to power the country. • In opposition to Edison was George Westinghouse and Tesla. Based on the designs of Tesla, Westinghouse saw how Alternating Current (AC) would have distinct advantages over DC. Why AC over DC? • AC has several advantages over DC, the most significant being that AC has the ability to be transformed, or changed to different voltages. • This allows power to be generated at high voltages, transmitted over long distances, then stepped down to usable household voltages. • DC cannot be transformed, so to overcome voltage drop, larger cables and higher voltages would have been necessary. • AC is more efficient and more cost effective, by using smaller cables, and has less watts loss and voltage drop than DC. War of the Currents • Edison steadfastly refused to believe he was wrong, and began a smear campaign against Westinghouse and the “evils” of AC. • Edison was successful in having the State of New York use AC to put a prisoner to death. The idea was that the public would associate AC with death. • Westinghouse successfully won the contract for generators at Niagara Falls as well as lighting the World’s Fair in 1893. Electricity and Safety • The Linemen of the 1890’s had no formal training and learned through trial and error. • As many as 1 in 2 linemen were killed during this time, either through electrocution or falling. • National Brotherhood of Electrical Workers, later to be the International Brotherhood of Electrical Workers (IBEW), was formed to ensure that safety standards were established and pay rates were equal and fair. Electricity and Safety • As was the case with linemen, electricians of the time also needed safety standards. • In 1895 there existed 5 different electrical standards, with different rules, creating much confusion and putting the public at risk. • A National Code was drafted in 1897, and was quickly adopted as the national standard. This is the National Electrical Code we use to this day. National Electrical Code • 90.1(A)- Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. • This means the rules are written to ensure an installation that won’t burn the structure down or give someone a shock. Might not be the most efficient way to do something, but will be safe if done to Code.
