A Power system earth
B Exposed conductive parts
Network type IT (Impedance Terra) :
The IT power distribution system has no direct connection to Protective Earth (PE). It is earthed
via a high ohmic impedance, so that the network is effectively behaving like an unearthed floating
network. The exposed conductive parts of the installation are directly connected to earth. In the
event of an initial earth leakage fault of a motor phase, the power supply continues. However, the
customer must detect the initial earth leakage fault. The fault must be indicated as an alarm.
A Power system earth
B Exposed conductive parts
C Impedance
CSA/UL versions
For UL designed control panels, calculations for cable sections and fuses are done according to
UL508a (Industrial control panels).
For CSA designed control panels, calculations for cable sections and fuses are done according
to CSA 22.2 (Canadian electrical code).
Standard conditions refer to maximum 3 copper conductors in raceway or cable with 85-90°C
(185-194°F) insulation at ambient temperature 30°C (86°F), operating at nominal voltage; cables
not grouped with other cables.
Worst case conditions refer to:
• ambient temperature > 30˚C (86 ˚F)
• maximum 3 copper conductors in raceway or cable with 85-90°C (185-194°F) insulation at
46°C (115°F) ambient temperature and operating at nominal voltage.
• cables not grouped with other cables
Fuse size is the maximum fuse size in order to protect the motor against short circuit. For CSA
fuse HRC form II, for UL fuse class RK5.
If the local conditions are more severe than the described standard conditions, the cables and
fuses for worst case conditions should be used.
Instruction book
52 AIF999999
To Next Page
Loading...
Need help?
General
