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Chapter 5 SMAW: Equipment and Supplies
Direct Current
Direct current (dc) flows in only one direction.
Current flows from one terminal of the welding
machine to the base metal. It then flows back to the
second terminal of the welding machine. On some
welding machines, the electrical leads are manually
reversed on the machine terminals. This changes the
direction of current flow. On other machines, a polar-
ity switch is flipped to electrically reverse the terminal
leads within the machine. See Figure 5-4. Welding
must be stopped and the electrode insulated from
the circuit whenever the polarity is changed.
The circuit polarity affects the selection of the cov-
ered electrode and how the covered electrode will
perform. Direct current electrode positive (DCEP)
used with the proper electrode produces deeper pen-
etration than direct current electrode negative
(DCEN). Most electrodes use DCEP.
Direct current electrode negative (DCEN) is used
with electrodes that do not produce deep penetration.
Asmall electrode using DCEN and a low-current setting
will produce a soft arc with only minimal penetra-
tion. Thus, DCEN, with proper electrodes, is used for
welding thin metals. DCEN is also used with some
electrodes to deposit weld metal quickly. DCEN can
melt an electrode more rapidly and deposit filler
metal at a faster rate than DCEP.
When limited to a certain polarity, the selection of
the electrode will depend on the type of polarity. If
only certain electrodes are available, the electrode will
determine the type of polarity. The polarity and the
electrode must always agree.
Alternating Current
Alternating current (ac) generally operates at 60
cycles per second in the United States. A cycle is a set
of repeating events, such as the flow and reversal of
flow in an electrical circuit. Alternating current flows
in one direction for 1/120 of a second, then reverses
its direction and flows for 1/120 of a second to form
one complete cycle. See Figure 5-5. The total time for
a cycle is 1/60 of a second:
1/120 sec + 1/120 sec = 1/60 sec
Frequency is a term used to describe the number
of cycles per second there are in ac power. Frequency
is measured in hertz (Hz). One cycle per second is the
same as one hertz. Thus, ac power at 60 cycles per sec-
ond is also called 60-hertz power.
Welding with ac and with ac electrodes produces
a medium depth of penetration. Many electrodes (but
not all) will work with alternating current. See
Chapter 7 and manufacturer's recommendations for
more information on electrodes.
SMAW Outfit
SMAW requires the use of proper protective
clothing and various tools, supplies, and equipment.
The welding outfit includes equipment required to
actually create a weld. The welding station includes
tools, supplies, and other items required to make
welding safe and comfortable. A complete SMAW
outfit includes the following:
• Welding machine/power source (dc, ac, or ac/dc).
• Electrode and workpiece leads.
• Electrode holder.
Selects alternating
current
Selects direct current
electrode positive
Selects direct current
electrode negative
Figure 5-4. This polarity switch has positions for DCEP, AC,
and DCEN.
Maximum
Current
1/120 sec
1/60 sec
One cycle or hertz (Hz)
Time
Maximum
0
0
1/120 sec + 1/120 sec = 2/120 sec = 1/60 sec
Figure 5-5. Alternating current plotted against time results in
an ac sine wave. The current increases from zero and returns to
zero. It then increases in the opposite direction and returns to
zero. The complete process is one cycle and takes 1/60 second.