Document 5kD81KrgmqvKZpjnGz90yegOR

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 welding under wet or humid at mospheric conditions where perspiration is a factor, a reliable automatic control device for reducing no-load voltage is recommended Cables Welding cable is usually purchased in 50-ft lengths, and several lengths may be used in one circuit Substantially insulated connec tors, or a capacity at least equivalent to that of the cable, should be used to splice or con nect cables Cable lugs used for connections should be securely fastened together by more than one bolt to give good electric contact The exposed metal parts of the lugs should be completely insulated 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 insu lation should be used The fact that welding circuit voltages are low may lead to laxity in keeping the welding cable in 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 pass age of persons and vehicles Welding cables should not lie m water or oil, m ditches or bottoms of tanks Rooms in which arc weld ing is to be done regularly should be permanendy wired with enough oudets so that ex tension cables will not have to be strewn about Electrodes and holders Arc welding is done with either a metallic or a carbon electrode The carbon electrode is usually a solid carbon or a graphite pencil, Vi in in diameter or larger, depending upon the amount of current used For gas-shielded metal arc welding, the i Fig 31-7 --Fully insulated electrode holder on the electrode lead and the ground clamp on the work lead have insulated locking-type plugs for connection to receptacles on the welding machine Courtesy Westinghouse Electric Corp electrode is a solid or cored bare wire For shielded metal arc welding, the electrode is a covered wire Electrode holders are used to connect the electrode to the welding cable supplying secondary current Fully insulated holders (Fig 31-7) are preferred because there is less likelihood of accidentally striking an arc with such holders, particularly in close quarters Electrode holders will become hot during welding operations if holders designed for light work are used on heavy welding, if connections between the cable and the holder are loose, or if ground connections are poor 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 in use Dipping hot electrode holders in water should be prohibited On light or medium heavy work, where 935