Table 7-1. - Cable Size Selection Guide

Figure 7-3. - Combination ac, dc transformer-rectifier arc welder.

RECTIFIER WELDING MACHINES. - Rectifier welders are single-phase or three-phase transformers that have selenium or silicon rectifiers added to direct current. Most of these machines have the capability of producing either ac or dc straight or reverse polarity current. By flicking a switch, the welder can select the current that best suits the job. Figure 7-3 shows an example of a combination ac/dc rectifier.

Cables

Welding cables carry the current to and from the workpiece. One of the cables runs from the welding machine to the electrode holder and the other cable connects the workpiece to the welding machine. The cable that connects the workpiece to the welding ma- chine is called the ground. When the machine is turned on and the operator touches the electrode to the work- piece, the circuit is completed, current begins to flow, and the welding process commences.

The welding cables must be flexible, durable, well insulated, and large enough to carry the required current. Only cable that is specifically designed for welding should be used. A highly flexible cable must be used for the electrode holder connection. This is necessary so the operator can easily maneuver the electrode holder dur- ing the welding process. The ground cable need not be so flexible because once it is connected, it does not move.

Two factors determine the size of welding cable to use: the amperage rating of the machine and the distance between the work and the machine. If either amperage or distance increases, the cable size also must increase. rectify (change) the output current from alternating to (See table 7-1.) A cable that is too small for the amperage or the distance between the machine and the work will overheat. On the other hand, larger size cables are more