Tweco 100 XT Ultra-Cut Plasma Cutting System - Manual (Page 31)

ULTRA-CUT 100 XT
Manual 0�5272 INSTALLATION �9
Obtain a power resistor of either 1200 (1.2K) ohms, 15�25W min, if using a 120V secondary or 2200 (2.2K) ohms,
25 �0W for a 220V secondary.
4. Assemble the transformer and power resistor in a metal box. Connect a  wire (w/gnd) power cord with ground
wire attached to the metal box for safety. If a plastic box is used instead, connect the transformer core and the
resistor mounts to the power cord ground wire. There should be a fuse ¼ � ½ A, in series with the transformer
primary. From the transformer secondary connect one wire to the utility safety ground. This could be the cutting
table frame, the ground terminal of the 120 or 220 VAC outlet or the test box if grounded as indicated.
An excellent ground measures 1 ohm or less. Up to  ohms is often acceptable, higher reduces the effectiveness
of the EMI suppression.
0.1 VAC = 1 OHM,
0.3 VAC = 3 OHM,
etc.
Triad N-68X
Utility (building) GND
11
5 V
AC
220 VAC
GND
Triad N-68X
F
F
11
5 V
AC
11
5 V
AC
11
5 V
AC
11
5 V
AC
GND
120 VAC
R = 1.2K, 15W
(2.2K, 25W for 220 VAC)
Ground Rod with other
connections removed
5. Increasing the ground rod length beyond 20 � 0 ft (6.1 – 9.1 m) does not generally increase the effectiveness
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. You may also try a chemical ground rod
devise. When these methods are used, periodic checking of the ground resistance is required to make sure the
ground is still good.
E. Routing Of Torch Leads
1. To minimize RF interference, position torch leads as far as possible from any CNC components, drive motors,
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 increased
chance of RF interference.