Ground-Fault Protection (G or ANSI 50N-TD/51N)
Ground-fault protection provides protection against phase-to-ground fault, which is more sensitive than protection based on phase current only. It is generally used in TN-S systems but could also be used in other earthing systems.
NOTE: Ground-fault protection is also called earth-fault protection.
Ground-fault protection is based either on the summation of the phases and neutral current or on the signal delivered by an external sensor, source ground return (SGR) current transformer through the MDGF module.
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HAZARD OF EQUIPMENT DAMAGE |
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With MicroLogic X control unit for IEC standard, when using source ground return (SGR) with MDGF module: oIg mode setting in OFF position is forbidden. oIg threshold setting must be ≤1,200 A. |
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Failure to follow these instructions can result in death, serious injury, or equipment damage. |
Ground-fault protection is available on:
oMicroLogic 6.0 X control units for IEC standard
oMicroLogic 6.0 X control units for UL standard
o3-pole and 4-pole circuit breakers
External sensors can be used:
oExternal Neutral Current Transformer (ENCT): measurement of the current on neutral. For information about the installation of ENCT, consult the instruction sheet on the Schneider Electric website: NHA14388.
oSource ground return protection: including ground-fault protection and an SGR sensor installed around the connection of the transformer neutral point to ground.
Ground-fault protection is powered by the current flowing through the internal current transformers of the circuit breaker and it does not require an additional external power supply.
The ground-fault current is calculated or measured according to the circuit breaker configuration, as shown in the following table.
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Circuit breaker configuration |
Ig ground-fault current |
|---|---|
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3P |
Ig = I1 + I2 + I3 |
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4P |
Ig = I1 + I2 + I3 + IN |
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3P + ENCT |
Ig = I1 + I2 + I3 + IN (ENCT) |
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3P or 4P + SGR |
Ig = ISGR |
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The ground-fault protection threshold Ig sets the level of ground-fault current at which the circuit breaker trips when reaching the ground-fault protection time delay tg. The time delay tg sets the length of time during which the circuit breaker carries a ground-fault within the ground-fault protection threshold Ig range. The time delay tg can be adjusted to: oFour setting values with I²t ON. In this case, the tripping curve is an inverse time curve up to 2 x Ir, meaning that the time delay decreases as the current increases. Above 2 x Ir, the tripping curve is a definite time curve with a constant tripping time. oFive setting values with I²t OFF. In this case, the tripping curve is a definite time curve with a constant tripping time. |
Ground-fault protection is based on the true RMS current of phases and neutral, up to harmonic 15.
In order to trip on an intermittent electrical fault, the control unit accumulates the intermittent currents in the ground-fault tripping range that do not last long enough to trigger a trip. This accumulation leads to shorter tripping times than those set.
Ground-fault protection can be enabled or disabled.
The ground-fault protection settings are:
oIg mode: enables (ON) or disables (OFF) ground fault protection
oIg: ground-fault protection threshold
otg: ground-fault protection time delay
oI²t (tg): ground-fault protection curve (I²t ON or I²t OFF)
They can be set as follows:
oOn the MicroLogic X display screen, at Home > Protection > I Ground Fault
oWith EcoStruxure Power Commission software (password-protected)
oWith EcoStruxure Power Device app (password-protected)
oBy sending a setting command using the communication network (password-protected).
The ground-fault protection can be duplicated when dual settings are activated.
Ig setting for MicroLogic 6.0 X IEC standard
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Setting |
Unit |
Range |
Step |
Factory setting |
Accuracy |
|---|---|---|---|---|---|
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Ig mode |
– |
ON/OFF |
– |
ON |
– |
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Ig(1) |
A |
0.2–1 x In |
10 A |
0.2 x In |
+/– 10% |
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(1) For In ≤ 400 A, the Ig setting range is 0.3–1 x In (factory setting: 0.3 x In) |
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Ig setting for MicroLogic 6.0 X UL standard
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Setting |
Unit |
Range |
Step |
Factory setting |
Accuracy |
|---|---|---|---|---|---|
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Ig mode |
– |
ON (always enabled) |
– |
ON |
– |
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Ig for In ≤ 400 A |
A |
0.3–1 x In |
0.1 x In |
0.3 x In |
+/– 10% |
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Ig for 400 A < In ≤1200 A |
A |
0.2–1 x In |
0.1 x In |
0.2 x In |
+/– 10% |
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Ig for In >1200 A |
A |
500–1200 A |
– |
500 A |
+/– 10% |
tg setting for MicroLogic 6.0 X IEC and UL standard
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Setting |
Unit |
Setting Value |
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tg with I²t OFF |
s |
0 |
0.1 |
0.2 |
0.3 |
0.4 |
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tg with I²t ON |
s |
– |
0.1 |
0.2 |
0.3 |
0.4 |
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Non-tripping time |
s |
> 0.02 |
> 0.08 |
> 0.14 |
> 0.23 |
> 0.36 |
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Maximum breaking time |
s |
< 0.08 |
< 0.14 |
< 0.20 |
< 0.32 |
< 0.50 |
The default tg time delay setting value is 0 s with I²t OFF.
NOTE: When tg is set to 0 s and I²t is changed to ON, the tg time delay is automatically set to 0.1.
Test the operation of ground-fault protection as follows:
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Step |
Action |
|---|---|
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1 |
Check that the circuit breaker is closed and the control unit is supplied with power (ready LED is flashing). |
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2 |
Use a thin screwdriver to briefly push in (< 1 s) the test button (T) on the front face of the MicroLogic X control unit. This action is recorded as an event. |
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3 |
The circuit breaker trips. An event is generated. |
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4 |
If the circuit breaker does not trip, an event is generated. Contact your field service representative. |
Zone Selective Interlocking (ZSI)
If ZSI IN is not set to 1 (open circuit between Z3 and Z4 terminals), the maximum breaking time is 0.08 s regardless of the tg setting value.
When ZSI IN is set to 1 and connected to the ZSI OUT of a downstream device (or when ZSI is not used, there is a jumper between the Z3 and Z4 terminals), the tg time delay is used.
The Ig threshold activates ZSI OUT (Z1 and Z2 terminals).
NOTE: MasterPact MTZ circuit breakers are delivered with a jumper installed between Z3 and Z4.
The function generates the following predefined events:
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Code |
Event |
History |
Severity |
|---|---|---|---|
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0x6403 (25603) |
Ig trip |
Trip |
High |
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0x641E (25630) |
I∆n/Ig test trip |
Trip |
High |
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0x6203 (25091) |
Ig start |
Protection |
Low |
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0x6303 (25347) |
Ig operate |
Protection |
Medium |
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0x142A (5162) |
I∆n/Ig test button pressed |
Diagnostic |
Low |
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0x1413 (5139) |
I∆n/Ig test - no trip |
Diagnostic |
High |
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0x142C (5164) |
Ig protection configured in OFF mode |
Diagnostic |
Medium |
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0x142D (5165) |
Ig function inhibited for test purpose |
Diagnostic |
Low |
Predefined events cannot be modified by the user. For general information about events, refer to Event management.
Protection events are generated as follows:
oThe start event is generated when the protection picks up.
oThe operate event is generated when the protection time delay elapses.
oThe trip event is generated when the circuit breaker tripping voltage release (MITOP) activates.
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Code |
Event |
Recommended actions |
|---|---|---|
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0x6403 (25603) |
Ig trip |
Reset the device or use the Power restoration assistant within the EcoStruxure Power Device app. |
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0x641E (25630) |
I∆n/Ig test trip |
Reset the device or use the Power restoration assistant within the EcoStruxure Power Device app. |
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0x1413 (5139) |
I∆n/Ig test - no trip |
Restart the test. If it fails again, replace the control unit. |
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0x142D (5165) |
Ig function inhibited for test purpose |
Exit the inhibition status after test. |
For information about resetting the circuit breaker after a trip due to an electrical fault, refer to the relevant document:
oMasterPact MTZ1 - Circuit Breakers and Switch-Disconnectors - User Guide
oMasterPact MTZ2/MTZ3 - Circuit Breakers and Switch-Disconnectors - User Guide
