Fuji Electric EW32EAG - Page 89

87
3
Selection and application
3-16 Ground fault protection in system applications
Continued
Comparison
item
Wiring system
TT IT
Circuit
diagram
L 1
L 2
L 3
N
L 1
L2
L3
Features s!LLEXPOSEDCONDUCTIVEPARTSOFTHEEQUIPMENTARECONNECTED
to a ground electrode that is completely separate from the
power supply ground.
s4HISSYSTEMISTHEMOSTCOMMONLYUSEDIN*APAN
s!LLEXPOSEDCONDUCTIVEPARTSOFTHEEQUIPMENTARECONNECTED
to a ground electrode that is completely separate from the
power supply ground.
s4HEPOWERSUPPLYISCONNECTEDTOGROUNDTHROUGHINSERTED
ground impedance or is completely disconnected from
ground.
s4HISWIRINGSYSTEMISWIDELYUSEDIN.ORWAY)N*APAN
however, greater emphasis is placed on circuits that supply
power without interruption rather than on those that shut down
the power supply.
Indirect
contact
protection
standards
50V t Ia × R
A
RA: Sum of the ground resistance and the protective conductor
resistance connected to exposed conductive parts.
Ia: Current that trips the MCCB automatically. (With an ELCB,
Ia is the rated sensitivity current I'n.)
The MCCB is as follows.
s7ITHINVERSETIMEDELAYCHARACTERISTICS)AISTHECURRENTTHAT
can trip the MCCB automatically within 5 s.
s7ITHINSTANTANEOUSTRIPPINGCHARACTERISTICS)AISTHESMALLEST
current that can trip the MCCB automatically.
50V t Id × RA
RA: Same as that on the left.
Id: Ground fault current at the first occurrence of a ground
fault where impedance between the phase conductor and
exposed conductor parts can be ignored. It is derived
from the leak current and total ground impedance of the
electrical equipment.
s)NSTALLANINSULATIONMONITORINGDEVICETHATINDICATESTHE
first occurrence of a ground fault in order to maintain an
uninterrupted power supply.
s0OWERSUPPLYSHUTDOWNCONDITIONSFOLLOWINGTHElRST
occurrence of a ground fault or with the second occurrence of
a ground fault should be provided separately.
Applicable
protective
device
s-##"ONLYIF2
A is very low however)
s%,#"
s)NSULATIONMONITORINGDEVICE
s-##"
s%,#"
Application
(design)
precautions
1. Select a suitable ground fault protection device for the
protection system.
2. Overcurrent breaking precautions:
s4HEADDITIONALCONDITIONSOUTLINEDABOVEMUSTBEPROVIDED
separately.
s/THERPRECAUTIONSARETHESAMEAS4.#ITEMSAND
11. Select a suitable ground fault protection device for the
protection system.
2. The power supply can shut down automatically when a
second ground fault occurs with overcurrent breaking.
3. Id t I'n when leak current breaking is used. Here, the power
supply can shut down automatically when the first ground
fault occurs.