Tweco 300 Ultra-Cut(March 2013) - Manual (Page 34)

INSTALLATION 3-10 Manual No. 0-5134
ULTRA-CUT 300
3. The cutting machine frame is then connected to the “Star” point using 1/0 AWG (European 50 mm 2 ) or larger
wire.
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 electri-
cal 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.
To test for a proper earth ground, refer to the following diagram. Ideally, the reading on the multimeter should be as
shown.
CAUTION
No other connections should be made at the ground rod being tested.