Tweco 400 XT Ultra-Cut Plasma Cutting System - Manual (Page 30)

ULTRA-CUT 400 XT
3-8 INSTALLATION Manual 0-5275
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. Con-
necting 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.