57
Chapter 5 SMAW: Equipment and Supplies
Open circuit voltage. Welding machines have a
maximum voltage, or open circuit voltage. Open circuit
voltage (OCV) is the voltage of the welding machine
when it is on, but is not being used. The maximum
OCV for most manual ac or dc machines is 80V.
This relatively low OCV protects workers from
electrical shock. The 80V OCV is still high compared
to the 5V-30V closed circuit welding voltage. An
OCV of 80V is required to start the arc easily. It is also
necessary to maintain the arc during ac welding.
Welding Leads
The electrical cable that connects the electrode
holder to a welding machine is the electrode lead. The
workpiece lead (ground) is the electrical cable that
connects the base metal to the welding machine.
On large welding machines, leads may be
required to carry 600A or more. Leads must have a
large diameter to carry such high current. They must
also be flexible so a welder can easily move them. As
many as 2500 fine conductors are used in a welding
lead to produce the flexibility required. Welding leads
must also be well insulated to prevent electrical
shock. They are usually insulated with a heavy rubber
or neoprene covering. See Figure 5-14.
Voltage and current are affected when the welding
leads are the wrong diameter. Electrical resistance in
the lead increases as its diameter decreases or its
length increases. Voltage drop (voltage loss) occurs
when electricity travels a long distance from the weld-
ing machine. A larger diameter lead is used to coun-
teract the voltage drop when long leads are required.
A greater amount of current flows in a larger diameter
lead when voltage drop is held to a minimum.
Figure 5-12. Rated output information is often shown on
welding machines. During ac operation, the output is 250
amperes at 30 volts. In dc, the output is 200 amperes at 28
volts.
Rated Duty Cycle
300
250
200
150
100
15 20 30 40 50 60 70 80 90 100
Welding
Amperes
% Duty Cycle
Figure 5-13. Duty cycle versus welding current graphs
should be provided with each new arc welding machine. The
duty cycle for this machine is 20% at 200A. At 100 amperes,
the machine may be used 100% of the time.
Figure 5-14. This arc welding lead shows the large number of
fine copper wires used. When twisted into larger bundles,
these fine wires give the lead its flexibility. The lead is then
covered with insulating material, cord reinforcement, and an
outer layer of rubber or plastic.