Atlas Copco GHS 900 VSD+ - Page 108

Instruction book
108 6996 0227 40
Calculation method for IEC:
 Single supply cables (3 phases + PE - configuration (1)):
 Add 10% to the total vacuum pump current (Itot 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 vacuum pump current (Itot 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 vacuum pump current (Itot 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: Itot= 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 sufficient. (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