Ambient temperature
Cable section 30 °C 40 °C 45 °C 50 °C 55 °C
25 mm² < 110 A < 96 A < 87 A < 78 A < 67 A
35 mm² < 137 A < 119 A < 108 A < 97 A < 84 A
50 mm² < 167 A < 145 A < 132 A < 119 A < 102 A
Calculation method for IEC:
• Single supply cables (3 phases + PE - configuration (1)):
• Add 10 % to the total compressor current (I
tot
Pack or I
tot
FF from the tables)
• Install the prescribed fuse on each cable
• Parallel supply cable (2 x 3 phases + PE - configuration (2)):
• Add 10 % to the total compressor current (I
tot
Pack or I
tot
FF from the tables) and divide by 2
• Multiply the ampacity of the cables with 0.8 (see table A.52.17 (52-E1))
• Install fuses of half the size of the recommended maximum fuse size on each cable.
• When using 2 x 3 phases + PE as in (3):
• Add 10 % to the total compressor current (I
tot
Pack or I
tot
FF from the tables) and divide by √3
• Multiply the ampacity of the cables with 0.8 (see table A.52.17 (52-E1))
• Fuse size: the recommended maximum fuse size divided by √3 on each cable.
• Size of the PE cable:
• For supply cables up to 35 mm²: same size as supply cables
• For supply cables larger than 35 mm²: half the size of the supply wires
Always check the voltage drop over the cable (less than 5 % of the nominal voltage is recommended).
Example: I
tot
= 89 A, maximum ambient temperature is 45 °C, recommended fuse = 100 A
• Single supply cables (3 phases + PE - configuration (1)):
• I = 89 A + 10 % = 89 x 1.1 = 97.9 A
• The table for B2 and ambient temperature = 45 ° C allows a maximum current of 93 A for a 50 mm²
cable. For a cable of 70 mm², the maximum allowed current is 118 A, which is sufficient. Therefore,
use a 3 x 70 mm² + 35 mm² cable.
If method C is used, 50 mm² is suffficient. (35 mm² for method F) => cable 3 x 50 mm² + 25 mm².
• Parallel supply cable (2 x 3 phases + PE - configuration (2)):
• I = (89 A + 10 %)/2 = (89 x 1.1)/2 = 49 A
• For a cable of 25 mm², B2 at 45 °C, the maximum current is 63 A x 0.8 = 50.4 A. So 2 parallel cables
of 3 x 25 mm² + 25 mm² are sufficient.
• Install 50 A fuses on each cable instead of 100 A.
Fuse calculations for IEC are done according to 60364-4-43 electrical installations of buildings, part 4:
protection for safety- section 43: protection against overcurrent. Fuse sizes are calculated in order to protect
the cable against short circuit. Fuse type aM is recommended but gG/gL is also allowed.
9.3 Reference conditions and limitations
Reference conditions
Air inlet pressure (absolute) bar 1
Air inlet pressure (absolute) psi 14.5
Air inlet temperature ˚C 20
Instruction book
2920 7104 10 91
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