nected to the work terminal of the welder. How-
it is best to use a ground rod inside the building,
ever, the welder will secure its ground through the
immediate y adjacent to the welder. Where the
ground lead of the welding circuit, to the work
building has a concrete floor, it will be necessary
table, and thence to the ground rod. The welder
to make an opening approximately 6 inches in di-
case should not be grounded by means of a third
ameter all the way through the concrete floor in
conduction in the primary cable. The weldar should
order to be able to properly treat the earth around
not be operated unless the case is grounded in ac-
the ground rod. The ground rod should be driven
cordance with foregoing.
below the level of the concrete surface and a cover
provided to avoid accidents.
g. Radiated Energy from Welder Equipment.
(2) Soil treatment for good ground. T h e
(1) Welder leads.
amount of reduction in radiation which a good
(a) The manner in which the noise is ra-
ground will produce will depend upon the ground
diated will depend upon the type of installation. In
resistance. The lower the resistance between the
an installation in which all of the power wiring,
ground rod and the surrounding earth, the lower
lighting wiring and telephone wires are shielded
will be the radiated signal. It has been found that
or are remote from the high frequency unit, the
if the earth around the ground rod is treated with
major part of the radiation will be directly from
a conducting solution known as an electrolyte the
the welding leads. In most cases, the amount of
signal will be lowered by an appreciable amount.
radiation will be too small to cause any interfer-
(3) Outside ground. Dig a circular trench
ence.
around the ground rod as shown. Place in this
(b) The amount of radiation is dependent
trench 20 to 30 pounds of copper sulphate, magne-
upon the length of the welding leads; the longer
sium sulphate, or salt, Then flood the trench sev-
the welding leads, the greater the radiation.
eral times and allow the water to sink into the
Therefore, the welding leads should be made as
ground, The trench can then be covered over with
short as possible, consistent with convenience in
earth. Normal rainfall will generally keep the
welding but should not exceed 25 feet.
ground moist enough to continually dissolve more
salt which will continually renew the electrolyte,
(2) Electromagnetic coupling.
thus maintaining a low ground resistance. (Refer
(a) In all cases, the initial radiation comes
to A, fig. 2-3. )
almost entirely from the welding leads. In installa-
(4) Inside ground. Fill the 6 inch diameter
tions where the power wiring is not in conduit or
hole around the ground rod with copper sulphate,
where there are unshielded lighting, telephone, or
magnesium sulphate, or rock salt and flood this a
control wires near the welder, another factor must
number of times until at least 8 to 10 pounds have
be considered.
dissolved and soaked into the earth. Then fill the
(b) Any circuit which carries current sets
hole with salt and let it remain in this condition. It
up around itself a field which extends for some
will be necessary to flood the hole periodically in
distance in all directions. Any other circuit which
order to keep enough electrolyte in the ground cir-
is within the influence of this field is said to be
cuit. Therefore, provide a removable cover instead
coupled to the first circuit. Thus, a circuit such as
of pouring concrete around the ground rod.
the welding leads which is carrying a high fre-
quency current can transfer a part of this current
(5) Grounding of welders.
from the welding leads to other unshielded power
(a) The welder should be grounded by run-
wiring, telephone wires, etc. These wires will in
ning a piece of braid from a connection on the
turn, act as antennas which will also radiate the
welder enclosure to the work terminal of the
high frequency current, Since these unshielded
welder. Do not run a separate ground to the enclo-
wires are usually considerably longer and higher
sure as, under certain conditions, this may greatly
than the welding leads, they are much better ra-
increase the amount of radio interference.
diators than the welding leads. Therefore, in an
installation of this type, the radiation into space
(b) The work or work table should not be
from the power wiring and other unshielded
grounded since the addition of a ground at this
wiring can be many times as great as the radia-
point will generally increase the amount of radia-
tion from welding leads alone (fig. 1-5 and 1-6).
tion. If, for any reason, it is impossible to avoid a
ground at the work or work table, then put the
(c) It has been established by tests and
measurements that, in most cases, very little of
ground rod near the work table, making this the
only ground in the system. The ground connection
the energy in the power wires reaches the power
wires by passing back through the welding equip-
to the enclosure of the welder can still be con-
2-5
