Ground-Fault Protection (G or ANSI 50N-TD/51N)

Presentation

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, an external neutral current transformer (ENCT), or a source ground return (SGR) current transformer through the MDGF module.

WARNING
HAZARD OF EQUIPMENT DAMAGE With MicroLogic X control unit for IEC standard, when using source ground return (SGR) with MDGF module: Ig mode setting in OFF position is forbidden. Ig threshold setting must be ≤1,200 A. Failure to follow these instructions can result in death, serious injury, or equipment damage.

Availability

Ground-fault protection is available on:

MicroLogic 6.0 X control units for IEC standard
MicroLogic 6.0 X control units for UL standard
3-pole and 4-pole circuit breakers

External sensors can be used:

External 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.
Source 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.

Operating Principle

The ground-fault current is calculated or measured according to the circuit breaker configuration, as shown in the following table.

Circuit breaker configuration	Ig ground-fault current
3P	Ig = I1 + I2 + I3
4P	Ig = I1 + I2 + I3 + IN
3P + ENCT	Ig = I1 + I2 + I3 + IN (ENCT)
3P or 4P + SGR	Ig = ISGR

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:

Four 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.
Five 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.

Setting the Protection

Ground-fault protection can be enabled or disabled.

The ground-fault protection settings are:

Ig mode: enables (ON) or disables (OFF) ground fault protection
Ig: ground-fault protection threshold
tg: ground-fault protection time delay
I²t (tg): ground-fault protection curve (I²t ON or I²t OFF)

They can be set as follows:

On the MicroLogic X display screen, at Home > Protection > I Ground Fault
With EcoStruxure Power Commission software (password-protected)
With EcoStruxure Power Device app (password-protected)
By sending a setting command using the communication network (password-protected).

The ground-fault protection can be duplicated when dual settings are activated.

Protection Settings

Ig setting for MicroLogic 6.0 X IEC standard

Setting	Unit	Range	Step	Factory setting	Accuracy
Ig mode	–	ON/OFF	–	ON	–
Ig⁽¹⁾	A	0.2–1 x In	10 A	0.2 x In	+/– 10%
(1) For In ≤ 400 A, the Ig setting range is 0.3–1 x In (factory setting: 0.3 x In)

Ig setting for MicroLogic 6.0 X UL standard

Setting	Unit	Range	Step	Factory setting	Accuracy
Ig mode	–	ON (always enabled)	–	ON	–
Ig for In ≤ 400 A	A	0.3–1 x In	0.1 x In	0.3 x In	+/– 10%
Ig for 400 A < In ≤1200 A	A	0.2–1 x In	0.1 x In	0.2 x In	+/– 10%
Ig for In >1200 A	A	500–1200 A	–	500 A	+/– 10%

tg setting for MicroLogic 6.0 X IEC and UL standard

Setting	Unit	Setting Value
tg with I²t OFF	s	0	0.1	0.2	0.3	0.4
tg with I²t ON	s	–	0.1	0.2	0.3	0.4
Non-tripping time	s	> 0.02	> 0.08	> 0.14	> 0.23	> 0.36
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.

Testing the Protection

Test the operation of ground-fault protection as follows:

Step	Action
1	Check that the circuit breaker is closed and the control unit is supplied with power (ready LED is flashing).
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.
3	The circuit breaker trips. An event is generated.
4	If the circuit breaker does not trip, an event is generated. Contact your Schneider Electric Services representative.

Zone Selective Interlocking (ZSI)

The ZSI characteristics and external wiring of the zone selective interlocking function, are described specifically.

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.

Predefined Events

The function generates the following predefined events:

Code	Event	History	Severity
0x6403 (25603)	Ig trip	Trip	High
0x641E (25630)	I∆n/Ig test trip	Trip	High
0x6203 (25091)	Ig start	Protection	Low
0x6303 (25347)	Ig operate	Protection	Medium
0x142A (5162)	I∆n/Ig test button pressed	Diagnostic	Low
0x1413 (5139)	I∆n/Ig test - no trip	Diagnostic	High
0x142C (5164)	Ig protection configured in OFF mode	Diagnostic	Medium
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:

The start event is generated when the protection picks up.
The operate event is generated when the protection time delay elapses.
The trip event is generated when the circuit breaker tripping voltage release (MITOP) activates.

Recommended Actions

Code	Event	Recommended actions
0x6403 (25603)	Ig trip	Reset the device or use the Power restoration assistant within the EcoStruxure Power Device app.
0x641E (25630)	I∆n/Ig test trip	Reset the device or use the Power restoration assistant within the EcoStruxure Power Device app.
0x1413 (5139)	I∆n/Ig test - no trip	Restart the test. If it fails again, replace the control unit.
0x142D (5165)	Ig function inhibited for test purpose	Exit the inhibition status after test.

Resetting a Trip Event

For information about resetting the circuit breaker after a trip due to an electrical fault, refer to the relevant document:

MasterPacT MTZ1 - Circuit Breakers and Switch-Disconnectors - User Guide
MasterPacT MTZ2/MTZ3 - Circuit Breakers and Switch-Disconnectors - User Guide