Document Bynz4d3yGMxbxL4Qn694LQaok

Electrical Hazards used in areas where it may come in contact with oils or solvents Cord for heating devices, such as electric irons and water heaters, is made with an in sulated covering which contains flame-retard ant or thermosetting compound, such as neoprene They are designed to resist high tempeiatuies and, in the case of neoprene, dampness Because the metal frames of portable elec trical equipment should be grounded, cord with a green-covered ground conductor should be used with a polarized plug and re ceptacle If plant circuits are not equipped with polarized receptacles, a third wire taped at intervals to the cord, to prevent its breaking and to prevent a tripping hazard, may be used One end of this third wire is electrically con nected to the frame of the tool, and the other end, which should be several feet longer than the cord, terminates m a spnng-type metallic clip-large enough to be clamped to a water pipe or other effective ground Extension lamps with brass shell sockets should be prohibited because the socket may become energized through contact with loose wires inside the socket, through abrasion of the insulation where the cord enters the socket, or through moisture in the socket in sulation Porcelain, composition, or rubbercovered sockets should be used Handles of portable lamp holders must be made of nonconductive material, and there should be no metallic connection between the lamp guard and the socket shell For use near exposed live parts, such as the rear of switchboards, the guard itself should be of nonconductive matenal Since extension lamps are sometimes used under conditions m which 120-volt shock may prove fatal, it is essential that safe cords and lamp holders be provided and that they be maintained in excellent condition In some plants the shock hazard of portable lamps is eliminated bv use of small portable transformers which step the lamp voltage down to 24 volts or less Special lamps for these units are rated at 75-watt capacity and give sufficient working light Test equipment Most electrical equipment is designed for safe operation under limited overload condi tions for varying penods of time Operators should be thoroughly familiar with the limita tions of their equipment and should be trained to observe and report abnormal condi tions Continued overload may introduce additional operating hazards by causing fire, short circuits, circuit failures, or machine failures Through the use of various types of electri cal testing meters, many of these conditions can be detected before they get out of control and cause damage The following types of equipment are standard and should be considered even by plants with limited budgets split-core am meter, voltmeter, ammeter, megohmmeter, ground fault indicators and locators, watt meter, industrial analvzer, recording instru ment, and specialized testing instruments The split-core ammeter can be used with out tapping into the circuit The instrument's core is slipped around one electric lead, and the scale is then read for the amount ofcurrent flow A current reading m excess of the rated full-load current may indicate an overload or a grounded motor winding When test leads are used with this instru ment, the line voltage can be checked to see if it equals the motor voltage rating This check is important because low voltage can cause excessive current flow which may result in a complete breakdown, arcing, or electrical fires Voltmeter and ammeter When the voltage and current used m a plant exceed the range of a split-core ammeter, separate instruments should be used a voltmeter to measure volt age and an ammeter to measure current When these two instruments are used, more accurate readings can be taken Also separate instruments are useful when simultaneous voltage and current readings are needed Such readings might be necessarv when tests are being made to check on voltage surges or dips and unusual power conditions while cur rent is on When the current to be measured exceeds the ammeter's range, shunts should be used for direct current measurement, and current transformers, for alternating current measure ment Likewise, when voltages exceed the voltmeter's maximum rating, resistors or potential transformers must be used to step 996