• 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.
Cable sizing according UL/cUL
Calculation method according UL 508A, table 28.1 column 5: allowable ampacities of insulated copper
conductors (75 °C (167 °F)).
Maximum allowed current in function of the wire size
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
Calculation method for UL:
• Single supply cables (3 phases + 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 phases + 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.
• When using 2 x 3 phase + 2 PE as in (3):
• Add 25 % to the total current from the tables and divide by √3
• Multiply the ampacity of the cables with 0.8 (see UL 508A table 28.1 continued)
• Fuse size: the recommended maximum fuse size divided by √3 on each cable.
Instruction book
2920 7109 23 123
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