Thermal Dynamics ULTRA-CUT 200 XT, Operating Manual

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ULTRA-CUT 200 XT
3-8 INSTALLATION Manual 0-5304
4. The plasma power supply work cable (see NOTE) is connected to the cutting table at the single point “Star” ground.
NOTE!
Do Not connect the work cable directly to the ground rod. Do not coil up excess ground or power
cables. Cut to proper length and reterminate as needed.
5. Make sure work cable and ground cables are properly connected. The work cable must have a solid connection to the cutting
table. The work and ground connections must be free from rust, dirt, grease, oil and paint. If necessary grind or sand down
to bare metal. Use lock washers to keep the connections tight. Using electrical joint compound to prevent corrosion is also
recommended.
6. The plasma power supply chassis is connected to the power distribution system ground as required by electrical codes. If
the plasma supply is close to the cutting table (see NOTE) a second ground rod is not usually needed, in fact it could be
detrimental as it can set up ground loop currents that cause interference.
When the plasma power supply is far away from the ground rod and interference is experienced, it may help to install a second
earth ground rod next to the plasma power supply. The plasma power supply chassis would then be connected to this ground
rod.
NOTE!
It is recommended that the Plasma Power Supply be within 20 - 30 ft (6.1 – 9.1 m) of the cutting
table, if possible.
7. The plasma control cable should be shielded with the shield connected only at the cutting machine end. Connecting the shield
at both ends will allow ground loop currents which may cause more interference than with no shield at all.
Creating An Earth Ground
1. To create a solid, low resistance, earth ground, drive a 1/2 in (12 mm) or greater diameter copper clad ground rod at least 6 - 8
ft (1.8 - 2.4 m) into the earth so that the rod contacts moist soil over most of its length. Depending on location, a greater depth
may be required to obtain a low resistance ground (see NOTE). Ground rods, typically 10 ft (3.0 m) long, may be welded end
to end for greater lengths. Locate the rod as close as possible to the work table. Install a ground wire, 1/0 AWG (European
50 mm2) 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.
D. Low Cost Ground Rod Tester
1. A key component of reduced EMI is a good low resistance earth ground rod. There are several very expensive instruments
to measure the ground but cost from several hundred to a few thousand dollars. Below is a low cost alternative which can
be constructed by qualified personnel familiar with established electrical construction and safety practices. Previously sug-
gested method using an incandescent light bulb will not work with GFCI outlets which are increasingly being used and the
bulbs are becoming obsolete.
2. This method, as well as the light bulb method and some of the expensive instruments, assumes the utility ground is perfect,
Zero ohms. It connects the rod being tested in series with the utility ground and measures the resistance of both in series.
If the utility ground is not zero ohms, no matter how good your rod is, you won’t get a low reading due the higher resistance
of the utility ground. Fortunately this is rare. Also if your rod is right next to another earth grounded structure you may get a
false lower reading of only resistance between that structure and your rod rather than to gnd.
NOTE!
In the United States most standard AC outlets are 120 VAC 60 Hz. Elsewhere most outlets are
220 VAC 50Hz.
3. Obtain a transformer rated for at least 25 VA with primary voltage and frequency matching your standard outlets. The trans-
former should have an isolated secondary of either 220 VAC (220 -240 is OK) or 120 VAC (110-120 is OK) and be rated for
at least 100 ma. The transformer could also have dual 115VAC primaries wired in series for 220V or in parallel for 120 VAC.
An example is Triad N-68X, shown below, rated 50VA, 50/60 Hz.
Obtain a power resistor of either 1200 (1.2K) ohms, 15-25W min, if using a 120V secondary or 2200 (2.2K) ohms, 25 -30W
for a 220V secondary.