Tweco FP-55 - Manual (Page 22)

INSTALLATION 3-6 Manual 0-2846
welded end to end for greater lengths. Locate the rod
as close as possible to the work table. Install a ground
wire, 1/0 (53,5 mm
2 ) or greater, between the ground
rod and the star ground point on the cutting table.
NOTE
Ideally, a properly installed ground rod will have a
resistance of three ohms or less.
To test for a proper earth ground using 115 VAC, refer
to the following diagram. Ideally, the reading on the
multimeter should be 3.0 VAC or less.
A-02971
+
_
Meter set to
VAC setting
Machine
Earth Ground
Neutral
Line (Hot)
100W
Light Bulb
115 or 230VAC
WARNING
Use extreme caution. This
test uses live voltage.
115VAC: 3.0 VAC
230VAC: 1.5 VAC
V ~
V
~
VR COM A
Figure 3-6 Ground Testing
2. Increasing the ground rod length beyond 20 - 30 ft
(6,1 – 9,1 m) does not generally increase the effective-
ness of the ground rod. A larger diameter rod which
has more surface area may help. Sometimes keeping
the soil around the ground rod moist by continuously
running a small amount of water into it will work.
Adding salt to the soil by soaking it in salt water may
also reduce its resistance. When these methods are
used, periodic checking of the ground resistance is re-
quired to make sure the ground is still good.
D. Routing Of Torch Leads
1. To minimize RF interference, position torch leads as
far as possible from any CNC components, drive mo-
tors, control cables, or primary power lines. If cables
have to pass over torch leads, do so at an angle. Do
not run the plasma control or other control cables in
parallel with the torch leads in power tracts.
2. Keep torch leads clean. Dirt and metal particles bleed
off energy, which causes difficult starting and in-
creased chance of RF interference.