Document LJmM7YBrvm08XyX3xNgo3LK67

WELDING AND CUTTING boos where the probability o{ contact with the open circuit voltage may be greater. Heavy duty AC welding machines (rat ings usually over 500 amp for automatic machine welding) are also built with open circuit voltages of 75 to 80 volts with a special tap to provide 100 volts where neces sary The tap may be needed to obtain rated output from the machine if the line voltage is low or if the voltage of the sec ondary circuit drops The tap should not be accessible to the welder for current adjust ment but should be under the control of a responsible electrician or supervisor Open circuit voltages should be as low as 50 volts on small AC welding machines used without expert supervision Since these machines are often used with low arc voltage electrodes and with leads not more than 20 ft long, the probability of a large voltage drop in the welding circuit is small Cables Welding cable is usually purchased in 50ft lengths, and several lengths may be used in one circuit. Substantially insulated con nectors, of a capacity at least equivalent to that of the cable, should be used to splice or connect cables Cable lugs used for connechons should be securely fastened to gether by more than one bolt to give good electnc 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 construc tion and across sharp comers, or run over by shop trucks Special cable with high quality insulation should be used. The fact that welding circuit voltages are low may lead to laxity m keeping the welding cable in good repair Operators and maintenance men should be instructed to see that defec tive cable is immediately replaced or re paired 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 passage of persons and vehicles Welding cables should not he in water or oil, in ditches or bottoms of tanks Rooms in which arc welding is to be done regularly should be permanently wired with enough outlets so that extension cables will not have to be strewn about Fig 29-7. Fully insulated electrode holder on the electrode lead and the ground clamp on the work lead have Insulated locking-type plugs far connection to re ceptacles on the welding machine. Courtesy WestmQhouie Electric Corp Electrodes and bolder; Arc welding is done with either a metallic or a carbon electrode The carbon electrode is usually a solid carbon or a graphite pen cil, X in in diam or larger, depending upon the amount of current used For gas-shielded metal arc welding, the electrode is a sobd 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 29-7) 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 bght work are used on heavy welding, if connections between the cable and the hold- 29-17