Tweco N7500 - Manual (Page 25)

Manual 89250890 3-9 SYSTEM COMPONENT DESCRIPTION
SYSTEM COMPONENT DESCRIPTION N7500
3.06 Selecting the Proper Electrode
Diameter
Your choice should be based on the depth and width of
the gouge you need. If you want a gouge 1-1/2 times
greater than the diameter of the electrode being used,
make the groove in two or more passes or oscillate
the Torch Head.
3.07 Keeping Electrodes Dry
Keep electrodes dry. Damp electrodes should be dried
before using. (Ten hours at 300°F [176.7°C]) Wet
electrodes may shatter from internal steam pressure
when an arc is struck.
POWER SUPPLY (SUPPLIED BY USER) FOR THE
N7500 SYSTEM
WARNING
Direct current/electrode positive (reverse
polarity) is required for the N7500 Sys-
tem. Use direct current/electrode negative
(straight polarity) for special applications.
DO NOT use alternating current with the
system.
CAUTION
Power Supplies must be rated for 100%
duty cycle at the amperage required for the
size (diameter) electrode used. Contact the
manufacturer of the Power Supply for parallel-
ing procedures or with questions concerning
amperage ratings and duty cycles.
NOTE
Recommendations are based on a 4 volt DC
drop per 100 ft. (30.48 m) length given is one-
half the sum of lengths of electrode and ground
leads. Inadequate grounding may cause cable
overheating. There should be at least 1 square
inch (6.45 cm 2 ) of contact per 1000 amps.
DC Welding Power Supply with a minimum Open-Circuit
Voltage (OCV) of 60 volts and 45 volts at rated load supply
the DC current for the N7500 System. Use single Power
Supplies rated at 1,000 or 1,500 amperes to get enough
amperage for larger diameter electrodes. Power Supplies
may be paralleled in combinations of two or more similar
units.
3.08 Secondary Power Cables (Welding Leads)
Recommended Number and Size of Secondary Cables
Amps
25 ft. (7.5 m) 50 ft. (15 m) 100 ft. (30 m) 150 ft. (46 m) 200 ft. (61 m) 250 ft. (76 m)
No. Size No. Size No. Size No. Size No. Size No. Size
100 4 4 1 1 1/0 1 2/0 1 4/0
200 3 2 1 1/0 1 3/0 1 3/0 3 3/0
300 2 1 1 3/0 2 2/0 2 4/0 4 4/0
400 2 1 1/0 1 4/0 3 3/0 3 4/0
500 1 1 2/0 2 2/0 3 4/0 4 4/0
600 1 1 3/0 2 3/0 3 4/0
800 1 3/0 1 4/0 2 4/0 5 4/0
1000 1 4/0 2 2/0 3 3/0
1200 2 2/0 2 3/0 3 4/0
1400 2 4/0 2 4/0 4 3/0
1600 3 3/0 2 4/0 4 4/0
1800 2 4/0 3 3/0
2000 3 4/0 3 4/0
Table 3-13: Power Cable Requirements
Choose the number and size of secondary power cables on the basis of the combined length of both the positive
(Electrode) and negative (work piece/ground) cables to ensure greatest efficiency and safe operation in terms of
100% duty cycle.