Tweco FP-55 - Manual (Page 21)

Manual 0-2846 3-5 INSTALLATION
Adapter
Pilot Lead
Torch Lead
Assembly
Negative/Plasma
Lead
Adapter Connector Negative/Plasma
Lead Connection
A-03528
Control Circuit
Connectors
Remote
Cable
Connector
Not
Used
Not
Used
Figure 3-5 Torch Lead Connections To Bulkhead
3.08 Ground Connections For
Mechanized Applications
A. Electromagnetic Interference (EMI)
Pilot arc initiation generates a certain amount of electro-
magnetic interference (EMI), commonly called RF noise.
This RF noise may interfere with other electronic equip-
ment such as CNC controllers, remote controls, height
controllers, etc. To minimize RF interference, follow these
grounding procedures when installing mechanized sys-
tems:
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 (42 mm
2 ) or larger
wire to a good earth ground (refer to paragraph ‘C’,
Creating An Earth Ground). The ground rod must be
placed as close as possible to the cutting table. Ide-
ally less than 10 ft (3,0 m), but no more than 20 ft
(6,1 m).
NOTE
All ground wires should be as short as possible.
Wires of long length will have increased resistance
to RF frequencies. Smaller diameter wire has in-
creased resistance to RF frequencies, so using a
larger diameter wire is better.
2. Components that are mounted on the cutting machine;
CNC controller, plasma remote controls, height con-
trollers, remote arc starters, etc., should be grounded
to the cutting machine frame (chassis) with at least a
12 AWG (4 mm
2 ) wire. Flat copper braid works even
better.
3. The cutting machine frame is then connected to the
“Star” point using AWG 6 (13,3 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.
5. Make sure work cable and ground cables are prop-
erly 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 elec-
trical codes. If the plasma supply is close to the cut-
ting table (see NOTE) a second ground rod is not usu-
ally 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 recommend that the Plasma Power Supply be
within 20 - 30 ft (6,1 – 9,1 mm) 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.
C. 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 re-
quired to obtain a low resistance ground (see NOTE).
Ground rods, typically 10 ft (3,0 m) long, may be