Protection Against Ground Faults
Introduction
Protection against ground faults is provided by:
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Earth-leakage protection in the case of low intensity fault currents (fault current limitation is linked to ground connection diagram TT or TN-S). Earth-leakage protection is provided by:
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Earth-leakage protection embedded in MicroLogic 4 and 7 trip units.
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VigiPacT Add-on earth-leakage protection module added to the circuit breaker.
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Ground-fault protection embedded in MicroLogic 6 trip units in the case of high intensity fault currents (this protection can be used only with ground connection diagram TN-S)
Embedded Earth-Leakage Protection
Earth-leakage protection is embedded within the MicroLogic 4 and 7 trip units.
The maximum value of IΔn depends on the circuit breaker frame size:
|
Circuit breaker frame size |
100 - 250 |
400 - 630 |
|---|---|---|
|
Maximum value IΔn |
5 A |
10 A |
The range provides two types of device:
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Trip devices trip on an earth-leakage fault
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Alarm devices measure and signal an earth-leakage fault without tripping:
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On the front face
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Through the SDx output contact
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The following illustrations show the two types of MicroLogic 4 trip units:
For more information about MicroLogic 7, refer to DOCA0141EN, ComPact NSXMicroLogic 5/6/7 Electronic Trip Units - User Guide.
Earth-Leakage Protection with VigiPacT Add-on
The VigiPacT Add-on is external to the trip unit and is designed to provide earth-leakage protection for the following situations:
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For system voltages up to 550 Vac
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For breaking capacity over 150 kA
The VigiPacT Add-on can be installed on ComPact NSX circuit breakers with thermal, thermal-magnetic, or MicroLogic 2, 5, and 6 trip units.
Illustration of VigiPacT Add-on installed on a ComPact NSX circuit breaker
Ground-Fault Protection
Ground-fault protection is embedded in MicroLogic 6 trip units. For more information, refer to DOCA0141EN, ComPact NSXMicroLogic 5/6/7 Electronic Trip Units - User Guide.
Setting the Earth-Leakage Protection
Installation standards require or recommend particular sensitivity and trip time values for earth-leakage protection:
|
Type of protection |
IΔn |
Δt |
Installation standards |
|---|---|---|---|
|
Protection against direct contact |
≤ 30 mA |
≤ 40 ms (1) |
Required |
|
Fire protection |
≤ 300 mA or ≤ 500 mA |
≤ 40 ms (1) |
Required if necessary |
|
Protection against indirect contact |
IΔn |
≤ 1 s |
Lowest possible recommended values of IΔn and Δt (the value of IΔn depends on the ground resistance) |
|
(1) Value of Δt for a fault current ≥ 10 IΔn |
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Setting the Ground-Fault Protection
Installation standards (in particular the NEC - National Electrical Code - defining installation rules in the USA) require or recommend the pickup and trip time values for ground-fault protection.
|
Location |
Ig |
tg |
NEC |
|---|---|---|---|
|
On the incoming supply to the low voltage distribution (and for In > 1,000 A) |
≤ 1,200 A |
– |
Required |
|
≤ 3,000 A |
≤ 1 s |
Required |
|
|
Downstream of the low voltage distribution |
Ig |
– |
Lowest possible recommended values for Ig |