Tweco 400 XT Ultra-Cut Plasma Cutting System With Automated Gas Control - Manual (Page 29)

ULTRA-CUT 400 XT
Manual 0-5306 INSTALLATION 3-7
A. Electromagnetic Interference (EMI)
Pilot arc starting generates a certain amount of electromagnetic interference (EMI), commonly called RF noise. This RF noise
may interfere with other electronic equipment such as CNC controllers, remote controls, height controllers, etc. To minimize RF
interference, follow these grounding procedures when installing mechanized systems:
B. Grounding
1. The preferred grounding arrangement is a single point or “Star” ground. The single point, usually on the cutting
table, is connected with 1/0 AWG (European 50 mm 2 ) or larger wire to a good earth ground (measuring less
than 3 ohms; an ideal ground measures 1 ohm or less. Refer to paragraph ‘C’, Creating An Earth Ground. The
ground rod must be placed as close as possible to the cutting table, ideally less than 10 ft (3.0 m), but no more
than 20 ft (6.1 m) from the cutting table.
NOTE
All ground wires should be as short as possible. Long wires will have increased resistance to RF fre-
quencies. Smaller diameter wire has increased resistance to RF frequencies, so using a larger diameter
wire is better.
2. Grounding for components mounted on the cutting table (CNC controllers, height controllers, plasma remote controls, etc.)
should follow the manufacturer’s recommendations for wire size, type, and connection point locations.
For Thermal Dynamics components (except Remote Arc Starter and Gas Control Module) it is recommended to use a minimum
of 10 AWG (European 6 mm 2 ) wire or flat copper braid with cross section equal to or greater than 10 AWG connected to the
cutting table frame. The Remote Arc Starter uses 1/0 earth ground wire and the Gas Control Module should use minimum #
4 AWG wire. The connection point must be to clean bare metal; rust and paint make poor connections. For all components,
wires larger than the recommended minimum can be used and may improve noise protection.
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 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.