Safety in Welding, Cutting, and Allied Processes

ANSI Z49.1:1999
expected current and duty cycles. Special attention shall
be paid to the insulation of cables used with equipment
which includes high voltage, high frequency oscillators.
11.3 Installation of Arc Welding Equipment
11.3.1 Code Requirements. Installation including
grounding, necessary disconnects, fuses, and type of
incoming power lines shall be in accordance with the
requirements of the current ANSI/NFPA 70, National
Electrical Code ¤ , and all local codes.
11.3.2 The Work. The workpiece or metal upon which
the welder welds shall be grounded independent of the
welding leads to a good electrical ground unless a qualified
person assures it is safe to work on an ungrounded
workpiece.
11.3.2.1 Grounding. Grounding shall be done by
locating the work on a grounded metal floor or platen, or
by connection to a grounded building frame or other satisfactory
ground. Care shall be taken however, to avoid
double grounding; otherwise, the welding current may flow
through a connection intended only for safety grounding
and may be of a higher magnitude than the grounding conductor
can safely carry.
E11.3.2 When the work terminal is grounded, care
should be taken to see that the workpiece is not separately
grounded. Refer to 11.3.2.1. Before welding is attempted
the operator should check to be sure that the worklead is
properly connected. This will eliminate the chance of welding
current being misdirected into the grounding conductor
system of other equipment. Misdirected welding current
can damage conductors which do not have adequate
ampacity.
E11.3.2.1 The work lead and work lead clamp are
sometimes incorrectly referred to as ground lead and
ground clamp. The work lead and the ground lead are
not the same. The work lead should not be referred to as
the grounding lead. It is preferable to connect the work
lead directly to the work. Hence, it is inappropriate to refer
to the lead as ground lead or the connection as
ground clamp. The work clamp should never be stored
by clamping it to any part of the grounded power source
frame. Grounding of electrical systems and circuit conductors
is done to limit voltages due to lightning, line voltage
surges, or unintentional contact with higher voltage
lines, and to stabilize voltage to ground during normal
operations.
It also facilitates overcurrent device operation in case
of ground faults. (See ANSI/NFPA 70, National Electrical
Code ¤ , Section 250-1, fine print note No. 1.) Grounding
of workpieces, equipment housings, metal cabinets and
frames, or other conductive material that form part of the
equipment is done to limit the voltage to ground on these
items. Limiting the voltage by grounding helps to prevent
accidental shocks when equipment is misconnected or insulation
fails. (See ANSI/NFPA 70, National Electrical
Code ¤ , Section 250-1, fine print note No. 2.)
Equipment used with ungrounded supply systems, such
as is used in naval shipboard systems, should be connected
in accordance with the requirements of the authority having
jurisdiction.
Special radio frequency grounding may be advisable
for equipment using high-frequency arc stabilizers. (See
Recommended Installation and Test Procedures for High
Frequency Stabilized Arc Welders, 1970, Arc Welding
Section of NEMA.)
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