Cable sizing according UL/cUL
Calculation method according UL 508A, table 28.1 column 5: allowable current of insulated
copper conductors (75 °C (167 °F)).
Maximum allowed current in function of the wire size
AWG or kcmil
Maximum current
AWG or kcmil
Maximum current
10
< 30 A
8
< 50 A
6
< 65 A
4
< 85 A
3
< 100 A
2
< 115 A
1
< 130 A
1/0
< 150 A
2/0
< 175 A
3/0
< 200 A
4/0
< 230 A
250
< 255 A
300
< 285 A
350
< 310 A
400
< 335 A
500
< 380 A
Calculation method for UL:
• Single supply cables (3 1 PE - configuration (1)):
• Add 25 % to the total current from the tables (see UL 508A 28.3.2: "Ampacity shall
have 125 % of the full load current")
• Install the prescribed maximum fuse on each cable
• Parallel supply cable (2 x 3 2 PE - configuration (2)):
• Add 25 % to the total current from the tables and divide by 2
• Multiply the ampacity of the cables with 0.8 (see UL 508A table 28.1 continued)
• Install fuses of half the size of the recommended maximum fuse size on each cable.
• Size PE cable:
• For supply cables up to AWG8: same size as the supply cables
• For supply cables larger than AWG8: use maximum allowed ampacity of the selected
supply cables and compare with value in table below (see CEC Part 1 table 17)
< 100 A: use AWG8
< 200 A: use AWG6
< 300 A: use AWG4
Always check the voltage drop over the cable (less than 5 % of the nominal voltage is
recommended).
Example of supply cable calculation:
I
tot
= 128 A, maximum ambient temperature is 45 °C,
recommended fuse = 150 A
• Single supply cables (3 1 PE - configuration (1)):
• I = 128 A + 25 % = 128 x 1.25 = 160 A
• For AWG2/0, the maximum current is 175 A, which is sufficient => use AWG2/0
• Install the prescribed maximum fuse (150 A) on each cable
• Parallel supply cable (2 x 3 2 PE - configuration (2)):
• I = (128 A + 25%)/2 = (128 x 1.25)/2 = 80 A
• For a AWG4, the maximum current is 85 A x 0.8 = 68 A, which is insufficient. For an
AWG3, the maximum current is 100 x 0.8 = 80 A. So 2 parallel cables of 3 x AWG3 + 2
x AWG8 are sufficient.
• Install 80 A fuses on each cable.
Instruction book
API480496
117
Summary of Contents for GA 37 VSD
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