Document b5kRevBNbVmYpdjR6obBEg4y1

34--Welding and Cutting metal is connected electrically to one side of the circuit, open circuit voltage of 150 volts may be allowed provided the following condi tions are present 1 All equipment and circuiting are fully in sulated and the operator cannot make elec trical contact other than through the arc itself, while the arc is mamtamed 2 Disconnecting or voltage reducing devices operate within a time limit not exceeding one second after breaking the arc Where neither side of the circuit is elec trically connected to the work, open circuit voltage of 300 volts is allowed if controls are present to prevent the operator from touching both sides of the circuit One hand should be used to operate control devices Also, the voltage should be disconnected automatically by a reliable switch instantly upon breaking the arc For AC or DC welding under wet or humid atmospheric conditions where perspiration is a factor, a reliable automatic control device for reducing no-load voltage is recommended Cables Welding cable is purchased in 50-ft lengths, and several lengths may be used in one circuit Substantially insulated connectors, of a ca pacity at least equivalent to that of the cable, should be used to splice or connect cables Cable lugs used for connections should be securely fastened together to give good electric contact The exposed metal parts of the lugs should be completely in sulated Welding cable is subjected to severe abuse if it is dragged over work under construction and across sharp comers, or run over by shop trucks Special cable with high quality in sulation should be used The fact that weld ing circuit voltages are low may lead to laxity m keeping the weldmg cable m good repair Operators and maintenance men should be instructed to see that defective cable is im mediately replaced or repaired On large jobs, there is likely to be much loose cable lying around Welders should keep this cable orderly and out of the way, preferably strung overhead to permit the pas sage of persons and vehicles Weldmg cables 962 should not he in water or oil, in ditches or bottoms of tanks Rooms m which arc weld mg is to be done regularly should be perma nently wired with enough outlets so that ex tension cables will not have to be strewn about Electrodes and holders Arc weldmg is done with either a metallic or a carbon electrode The carbon electrode is usually a solid carbon or a graphite pencil, X m in diameter or larger, depending upon the amount of current used For gas-shielded metal arc weldmg, the electrode is a solid or flux-cored wire For shielded metal arc weldmg, the electrode is a covered wire. Electrode holders as used for shieldedmetal arc welding (SMAW) are used to con nect the electrode to the welding cable supply ing secondary current Fully insulated hold ers (Fig 34-7) are preferred because there is less likelihood of accidentally striking an arc with such holders, particularly in close quar ters Electrode holders will become hot during welding operations if holders designed for light work are used on heavy weldmg or if connections between the cable and the holder are loose If a holder of the correct size for the elec trode cannot be used, an extra holder should be provided so that one can cool while the other is m use Dipping hot electrode holders in water should be prohibited On light or medium heavy work, where light, extremely flexible cables are used, hold ers may be attached directly to the work lead running to the machine On heavier work, welders generally prefer a short length at tached to the holder, which is more flexible than the mam work lead Properly insulated cables of weight and flexibility which will not inconvenience the welder are available Automatic and semiautomatic welding Arc weldmg may also be done automatically or semiautomatically to increase the speed of weldmg and provide more uniform weld qual ity Machme weldmg is especially efficient for long welds or where a high rate of pro duction is mvolved and the work can be jigged The rate of electrode feed and arc