TM 5-3431-225-15
the source. The intensity and frequency of the
radiation can be altered over wide limits by chang-
and connect suitable pipe and fittings to the weld-
ing machine. If a portable water coolant system
ing the location and relative position of the weld-
is used, connections should be made directly to
ing leads and work. If possible, loops and sus-
the electrode holder water connections, by-pass-
pended sections should be avoided.
ing the welding machines water valve.
(d) Pick-up and reradiation from power
connect suitable pipe and fittings to the welding
off rapidly with distance, the field strength in
machine.
the immediate vicinity of the welding area may
be extremely high. Unshielded wiring and un-
Note. When installing the welding machine, allow at
grounded metallic objects in this strong field
least 18-inches clearance on all sides for proper ventila-
tion.
may pick up the direct radiation, conduct the
energy for some distance, and produce a strong
e. Radio Interference.
interference field in another area. This is usually
(1) The following information is necessary
the most troublesome source of interference, but
to make a proper installation of the high fre-
careful adherences to proper installation proce-
queney arc welding equipment described in this
dure as outlined in this booklet will minimize
manual. The manufacturer of the equipment cov-
this type of interference.
ered herein has conducted approved field tests
(3) The specific installation instructions
and certifies that the radiation can reasonably be
for making the proper primary connections to the
expected to be within the legal limits if the cor-
equipment as outlined in the manual furnished
rect installation procedures, as outlined, are fol-
with the equipment, should be followed care-
lowed. The importance of a correct installation
fully. Only solid metallic conduit or conduit of
cannot be over-emphasized since case histories of
"equivalent electrical shielding ability" should
interference due to high frequency stabilized arc
be used to enclose the primary power service
welding machines have shown that invariably
leads. Solid metallic shielding shall enclose the
all inadequate installation was at fault.
primary power service to the equipment from a
(2) In a high frequency stabilized arc weld-
point 50 feet from the equipment in an unbroken
ing machine installation, interfering radiation
run. This shielding shall be grounded at the
can escape in four distinct ways as outlined be-
farthest point from the equipment and should
low:
make good electrical contact with the casing of
(a) Direct radiation from the welding
the equipment. The ground should be in accord-
machine. This is radiation that escapes directly
ance with the specifications outlined in para 2-4a
from the welding machine case. This is very pro-
and b and as shown in figure 2-2. Care should
nounced if access doors are left open and unfas-
be taken that paint or corrosion at the junction
tened and if the welding machine case is not
of conduit and case do not interfere with good
properly grounded. Any opening in the metal
electrical contact. There shall be no gap in this
welding machine case will allow some radiation
shielding run. This simply means that within 50
to escape, The high frequency unit of this cer-
feet of the equipment, no portion of the power
tified equipment is adequately shielded to pre-
wires serving the equipment shall be unshielded.
vent direct radiation of any consequences if prop-
If there is any question about the electrical ef-
er grounding is carried out.
ficiency of the joints between individual conduit
(b) Direct feedback to the power l i n e .
sections, outlet boxes and the equipment case,
High frequency energy may get on the power
line by direct coupling inside the equipment or
copper strap or wire across the joint as shown in
the high frequency unit, the power line then
serving as a radiating antenna. By proper shield-
(4) The location of the equipment should
ing and filtering, direct coupling is prevented in
be chosen with respect to nearness to a suitable
this certified equipment.
ground connection. The equipment case, firmly
bonded to the power conduit, should be grounded
(c) Direct radiation from welding leads.
to the work terminal of the equipment with a
Direct radiation from the welding leads, al-
copper cable or braid with rated current carrying
though very pronounced, decreases rapidly with
equal to or greater than that of the power service
distance from the welding leads. By keeping the
wires. The "work" output terminal of the equip-
welding leads as short as possible, the operator
ment should then be grounded to a "good elec-
can do a great deal to minimize interference from
2-2
