TM 5-3431-225-15
(7) Frequent reference is made to a "good
trical ground" with a short length of welding
ground" in previous sections. Although there is
cable of the same capacity as the "work lead"
considerable leeway in the interpretation of this
term, for the purpose covered in this manual the
tion, all access and service doors shall be closed
following specifications apply: A "ground" con-
and properly fastened. Spark gap settings shall
nection should be made to a driven rod at least 8
be maintained at the minimum separation consist-
feet long and driven into moist soil. A cold water
ent with satisfactory welding results (fig. 3-16).
pipe can be used in place of the ground rod pro-
(5) In order to minimize direct weld lead
vided it enters the ground within 10 feet of the
radiation, the welding leads (electrode lead and
equipment to be grounded. All leads connecting
work lead) must be kept as short as possible.
the point to be grounded to the ground rod or
Certification tests on this machine have been
pipe should be as short as possible since the
made with leads 25 feet long. Considerable im-
ground lead itself can become an effective radi-
provement in radiation minimization can be had
ating antenna. The effectiveness of a ground in
by shortening the leads as much as possible.
reducing interference depends upon the ground
Keeping the electrode lead and ground or work
conductivity. In certain locations it may become
lead as close as possible and on the floor serves
necessary to improve the ground conductivity by
to reduce the radiation (fig. 2-2D).
treating soil around the ground rod with a salt
(6) The most serious source of interference
solution.
is reradiation from wires that are located near
(8) It is frequently thought that operation
the welding area. Any ungrounded electrical con-
of high frequency stabilized arc welding equip-
ductor in the strong "directly radiated" field,
ment in metallic buildings will completely elim-
produced by the welding leads, serves as a pick-
inate troublesome radiation. This, however, is a
up device and may conduct the interference for
false assumption. A metallic building structure,
some distance and reradiate strongly at another
if properly grounded, may serve to reduce direct
location. For purpose of simplification and stand-
radiation from the weld zone but will have no
ardization, the space all around the weld zone
effect on conducted interference and reradiation.
at a distance of 50 feet in all directions is re-
As a result, all installation requirements men-
ferred to as the high field intensity (H.F.I.)
tioned above must be complied with. If the me-
tallic building is not properly grounded, bond-
type, all wiring in the H.F.I. zone shall be in
ing to several good electrical grounds placed
rigid metallic conduit, lead covered cable, copper
around the periphery of the building will give
braid or material of equivalent shielding effi-
reasonable assurance that the building itself is
ciency. Ordinary flexible helically wrapped me-
not contributing to the radiation.
tallic conduit, commonly referred to as "B. X."
f. Check List of High Frequency Stabilized
is not satisfactory for shielding, and should not
Arc Welding Equipment Installation.
be used. The shield on all wiring should be
(1) Has the equipment been located so that
grounded at intervals of 50 feet and good elec-
ground leads can be kept short?
trical bonding between sections shall be main-
(2) Are the power leads serving the unit
tained. This shielding requirement applies to all
in conduit?
wiring, including telephone, inter-communica-
(3) Is there good electrical contact between
tion, signal and control and incidental service.
power conduit and case?
Extreme precaution should be taken to make sure
(4) Do the conduit couplings make good
that the location of the zone is chosen so that
electrical contact? (If in doubt, use bonding.)
none of the conditions are voided by unshielded
(5) Is there good electrical contact between
wires off the premises but still within the radial
conduit and switch on service boxes?
dimensions of the H.F.I. zone. This 50 foot
(6) If rigid metallic conduit is not used, is
H.F.I. zone is a minimum that is imposed on the
the shielding used of equivalent shielding effi-
installation. Certification tests by the manufactur-
ciency? (Copper sleeving, lead covered cable,
er are based on this limit. Keeping unshielded
etc., is satisfactory. Spirally wound flexible me-
wires farther than 50 feet from the weld zone
tallic conduit is not suitable.)
will materially aid in minimizing interference.
(7) Is the conduit system grounded at a
If it is impossible to relocate unshielded wires,
point at least 50 feet from the equipment?
that section within the H.F.I. zone, should be
placed in conduit and each end of the conduit
(8) Is the conduit run complete (without
section grounded.
any gap) in the H.F.I. zone?
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