Littelfuse SE-330AU User manual

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SE-330AU MANUAL
NEUTRAL-EARTHING-RESISTOR MONITOR
Revision 4-I-101817
Copyright Ó2017 Littelfuse Startco
All rights reserved.
Document Number: PM-1210-EN
Printed in Canada.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
TABLE OF CONTENTS
SECTION PAGE
1 General ................................................................. 1
1.1 Modern Resistance-Earthed Systems .................... 1
1.2 SE-330AU NER Monitoring ................................. 1
2 Operation.............................................................. 2
2.1 Settings .................................................................. 2
2.1.1 EF Trip Time.............................................. 2
2.1.2 EF Trip Level ............................................. 2
2.1.3 VNTrip Level ............................................. 2
2.1.4 Configuration Settings ............................... 2
2.1.4.1 Earth-Fault-Trip Latch (S3) .......... 2
2.1.4.2 Resistor-Fault-Trip Latch (S4)...... 2
2.1.4.3 Sensing-Resistor Selection (S5).... 3
2.1.4.4 Frequency (S6) .............................. 3
2.1.4.5 Upgrade Mode (S8)....................... 3
2.1.5 Resistor-Fault Trip Time............................ 3
2.1.6 Resistor-Fault Trip Level ........................... 3
2.1.7 Geo-Magnetic Filter ................................... 3
2.2 Calibration ............................................................. 3
2.3 CT Detection ......................................................... 3
2.4 Trip Indication and Reset ...................................... 4
2.5 Remote Operation.................................................. 4
2.6 Relay K1 LED ....................................................... 4
2.7 Unit Healthy Output .............................................. 4
2.8 Diagnostic LED ..................................................... 4
2.9 Analog Output ....................................................... 4
3 Installation............................................................ 6
3.1 SE-330AU ............................................................. 6
3.2 Sensing Resistor .................................................... 6
3.3 Earth-Fault CT....................................................... 6
3.4 Isolated Earth Connection ................................... 24
4 Data Interfaces................................................... 25
4.1 SD Card ............................................................... 25
4.1.1 Datalogging .............................................. 25
4.1.2 Firmware Upgrade ................................... 25
4.2 USB Interface ...................................................... 25
4.3 Network Communications................................... 25
5 Troubleshooting................................................. 26
6 Technical Specifications .................................... 28
6.1 SE-330AU ........................................................... 28
6.2 Sensing Resistors................................................. 30
6.3 Current Sensors ................................................... 31
7 Ordering Information ....................................... 31
8 Warranty ............................................................ 32
9 Test Procedures.................................................. 33
9.1 Resistor-Fault Tests ............................................. 33
9.1.1 Calibration and Open Test ....................... 33
9.1.2 Voltage Test ............................................. 33
9.2 Sensing-Resistor Test .......................................... 33
9.3 Analog-Output Test ............................................. 33
9.4 Earth-Fault Performance Test.............................. 34
Appendix A SE-330AU Revision History ................... 35
LIST OF FIGURES
FIGURE PAGE
1 Configuration Switches ......................................... 3
2 Analog-Output Connections.................................. 4
3 SE-330AU Connection Diagram ........................... 7
4 SE-330AU Outline and Panel-Mounting Details .. 8
5 SE-330AU Outline and Surface-Mounting
Details.................................................................... 9
6 SE-IP65CVR-G Weatherproof Cover Outline .... 10
7 SE-IP65CVR-G Weatherproof Cover
Installation ........................................................... 11
8 ER-600VC Sensing Resistor ............................... 12
9 SE-MRE-600 Moisture Resistant Enclosure ......... 13
10 ER-600VC Installed in SE-MRE-600 ................... 14
11 ER-5KV Sensing Resistor ................................... 15
12 ER-5WP Sensing Resistor................................... 16
13 ER-15KV Sensing Resistor ................................. 17
14 ER-25KV Sensing Resistor ................................. 18
15 ER-35KV Sensing Resistor ................................. 19
16 EFCT-1 Earth-Fault Current Sensor.................... 20
17 SE-CS30-70 Earth-Fault Current Sensor............. 21
18 EFCT-26 and SE-CS30-26 Earth-Fault
Current Sensors ................................................... 22
19 RK-332 Remote Indication and Reset................. 23
20 PGA-0520 Analog Percent Current Meter .......... 23
21 Simplified Isolated-Earth Connection ................. 24
22 Earth-Fault-Test Circuits ..................................... 34
LIST OF TABLES
TABLE PAGE
1 Typical Values for Tripping Systems.................... 5
2 Earth-Fault-Test Record ...................................... 34
DISCLAIMER
Specifications are subject to change without notice.
Littelfuse Startco is not liable for contingent or
consequential damages, or for expenses sustained as a result
of incorrect application, incorrect adjustment, or a
malfunction.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
1. GENERAL
1.1 MODERN RESISTANCE-EARTHED SYSTEMS
A high-resistance-earthed system uses a neutral-
earthing resistor (NER) with a low let-through current to
limit earth-fault current. This is an improvement over
low-resistance or solidly-earthed systems because, in
those systems, an earth-fault flash hazard exists and an
earth fault can result in substantial point-of-fault damage.
High-resistance earthing eliminates these problems and
modern earth-fault protection operates reliably at low
current levels. Furthermore, the probability of an arc-
flash incident is significantly reduced in a high-resistance
NER system.
NER selection depends on system charging current.
System charging current is the capacitive current that
flows to earth when a bolted earth fault occurs. This
current can be calculated or measured. For small systems,
the magnitude of charging current can be conservatively
estimated as ½A per 1,000 kVA on low-voltage systems
and 1 A per 1,000 kVA on medium-voltage systems.
Choose an NER with a let-through current larger than
the system charging current. Set the pick-up current of
earth-fault devices at or below 10% of the NER let-
through current for systems up to 1.1 KV and 20% of the
NER let through current for systems above 1.1 KV.
Use earth-fault devices with a definite-time characteristic
to achieve time coordination. Use the same pick-up current
for all earth-fault devices—this value must be larger than
the charging current of the largest feeder. Select an NER
with a let-through current between five and 10 times the
pick-up current of the earth-fault devices.
Do not use an earthing transformer with a low-voltage
resistor:
• The combined cost of a transformer and a low-
voltage resistor is more than the cost of a resistor
rated for line-to-neutral voltage.
• A transformer saturated by an earth fault through a
rectifier can make earth-fault protection inoperative.
• Transformer inrush current up to 12 times rated
current can cause an earth-fault voltage larger than
expected.
• A parallel transformer winding makes it difficult to
monitor NER continuity.
• A transformer can provide the inductance necessary
to cause ferroresonance if the NER opens.
Following these guidelines will reduce the flash hazard,
reduce point-of-fault damage, achieve reliable earth-fault
protection, and ensure a stable system not subject to
ferroresonance.
1.2 SE-330AU NER MONITORING
The SE-330AU is a microprocessor-based neutral-
earthing-resistor monitor that detects NER failures and
earth faults in resistance-earthed systems. The SE-330AU
measures NER resistance, NER current, and transformer
or generator neutral-to-earth voltage. The components
required to monitor an NER are an SE-330AU, an ER-series
sensing resistor, and a current transformer (CT).
Power-circuit elements, other than neutral-connected
NER’s, that purposefully connect the power system to
earth may not be compatible with SE-330AU NER
monitoring. These elements include single-phase earthing
transformers, earthed-wye-primary potential transformers
(PT’s), and earthed-wye-primary power transformers.
The SE-330AU continuously measures NER resistance
in an unfaulted system. It will trip on resistor fault if
NER resistance varies from its calibrated value. When an
earth fault occurs, voltage is present on the neutral and
NER current will flow if the NER is healthy. The
SE-330AU will trip on earth fault if fault current exceeds
the EF TRIP LEVEL setting for an interval greater than
the EF TRIP TIME setting. However, if the NER fails
and creates an open circuit during an earth fault, it is
possible for fault resistance to satisfy the NER resistance
measurement. To detect this double-fault condition, the
SE-330AU measures neutral voltage. If neutral voltage
exceeds the VNTRIP LEVEL setting, and if NER current
is less than 5% of the current transformer (CT) rating, the
SE-330AU will trip on resistor fault. If the resistor-fault
circuit is tripped and the neutral voltage exceeds the VN
TRIP LEVEL setting for an interval greater than the EF
TRIP TIME setting, the earth-fault circuit will also trip.
Earth-fault current is sensed by a sensitive CT (EFCT-x
or SE-CS30-x). The trip level of the earth-fault circuit is
adjustable from 0.125 to 5 A for the EFCT-x and 0.75 to
30 A for the SE-CS30-x. Trip time is adjustable from 0.1
to 0.5 seconds. Open-CT detection is provided with a
fixed 2-second time delay.
The SE-330AU has four output relays. Relay K1 is the
trip relay. Relays K2 and K3 provide earth-fault and
resistor-fault indication. K4 is a solid-state relay that
provides UNIT HEALTHY indication. Relay K1
operates in the fail-safe mode for undervoltage
applications.
Additional features include LED trip indication, trip
memory, front-panel and remote reset, 4-20-mA analog
output, trip event recorder, USB local communications,
microSD™ data logging, and optional network
communications.
The SE-330AU is compatible with lockout earth-fault
protection devices¾the on line phase-to-earth resistance
added by coupling components must be above the
SE-330AU NER-failure-detection resistance.
The SE-330AU provides additional features over the
SE-330AU legacy model (revision 01 or less):

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
• When the trip level is set to MEM, the earth-fault trip
setting is defined by an internal non-volatile memory
variable. Range is 2 to 100% in 1% increments of the
CT-primary rating.
• Indication relays can be set to fail-safe or non-fail-
safe.
• The number of trip records has been increased to 100
and includes date and time stamping.
• A microSD™ card interface can be used for long-
term data logging and firmware updates. A
microSD™ card and a microSD-to-SD adapter is
included. See Section 4.1.
• For ease of connection to new devices, the RS-232
interface has been replaced by a Mini B USB port.
• Dual Ethernet ports are available with support for
fiber-optic and RJ45 interfaces.
• The IEC 61850 protocol has been added.
2. OPERATION
2.1 SETTINGS
2.1.1 EF TRIP TIME
EF TRIP TIME (definite time) is adjustable from
0.1 to 0.5 seconds. Time-coordinated earth-fault protection
requires this setting to be longer than the trip times of
downstream earth-fault devices.
A trip-time accumulator provides an earth-fault memory
function for detection of intermittent faults. The
accumulated time increases when an earth fault is detected
and decreases when an earth fault is not detected. A trip
will eventually occur when the time for fault current above
the trip level is greater than the time for fault current below
the trip level.
2.1.2 EF TRIP LEVEL
The SE-330AU uses a Discrete-Fourier Transform
(DFT) Algorithm to measure the fundamental component
of NER current.
Choose an NER let-through current and an earth-fault
trip level according to the guidelines in Section 1.1.
Earth-fault current is sensed by a sensitive CT (EFCT-x
or SE-CS30-x). The trip level of the earth-fault circuit is
adjustable from 0.125 to 5 A for the EFCT-x and 0.75 to
30 A for the SE-CS30-x.
When EF TRIP LEVEL is set to MEM, the earth-fault
setting stored in non-volatile memory is used. This
parameter must be set using a PC running the SE-MON330
software connected to the USB interface. The setting range
is 2 to 100% of CT-primary rating in 1% increments. For
example, if the MEM parameter is set to 15% (default), the
trip level will be 0.75 A or 4.5 A when using the EFCT-x or
SE-CS30-x respectively. Typical values are shown in Table
1. For other systems, refer to the NER Monitor Set-Point
Assistant at www.littelfuse.com/relayscontrols. The Set-
Point Assistant is included with the SE-MON330 software.
2.1.3 VN TRIP LEVEL
The SE-330AU uses a DFT algorithm to measure the
fundamental component of neutral voltage (VN).
If neutral voltage is greater than the VNTRIP LEVEL
setting for the duration of the resistor-fault trip time and
earth-fault current is less than 5% of the CT rating, the
SE-330AU will trip on resistor fault. If the resistor-fault
circuit is tripped and the neutral voltage exceeds the VN
TRIP LEVEL setting for an interval greater than the EF
TRIP TIME setting, the earth-fault circuit will also trip.
The VNTRIP LEVEL range is 20 to 2,000 V with
switch S5 in the 20-kW(Vx1) position, and the range is
100 to 10,000 V with switch S5 in the 100-kW(Vx5)
position. Calculate the voltage across the NER when
NER current is equal to the pick-up current of the earth-
fault circuit. Set the VNTRIP LEVEL at the next largest
value. See Fig. 1 and Section 2.1.4.3.
Typical values are shown in Table 1. For an NER
resistance greater than 2 kW, use a 100-kWsensing resistor.
For other systems, refer to the NER Monitor Set-Point
Assistant at www.littelfuse.com/relayscontrols.
NOTE:A resistor-fault trip is held off if the earth-fault
current is above 5% of the CT rating.
2.1.4 CONFIGURATION SETTINGS
Eight configuration switches (S1 to S8) and a
calibration button are located behind the access cover on
the front panel. See Fig. 1.
2.1.4.1 EARTH-FAULT-TRIP LATCH (S3)
Set switch S3 to select latching or non-latching earth-
fault-circuit operation. See Section 2.4.
2.1.4.2 RESISTOR-FAULT-TRIP LATCH (S4)
Set switch S4 to select latching or non-latching resistor-
fault-circuit operation. See Section 2.4

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 1. Configuration Switches.
2.1.4.3 SENSING-RESISTOR SELECTION (S5)
Set switch S5 to the resistance of the sensing resistor. For
the ER-600VC, ER-5KV, and ER-5WP select 20 kW. For
the ER-15KV, ER-25KV, and ER-35KV, select 100 kW.
Switch S5 sets the VNTRIP LEVEL range. See
Section 2.1.3.
2.1.4.4 FREQUENCY (S6)
Set switch S6 to 50 or 60 Hz to tune the digital filter to
the line frequency of the monitored system.
2.1.4.5 UPGRADE MODE (S8)
The microSD™ card is used for firmware upgrades.
See Section 4.1.2 for upgrade instructions.
NOTE: An upgrade causes an SE-330AU restart and this
may cycle the output relays.
2.1.5 RESISTOR-FAULT TRIP TIME
The resistor-fault trip time can be adjusted from 12
(default) to 60 seconds using the SE-MON330 software or
via network communications.
2.1.6 RESISTOR-FAULT TRIP LEVEL
The resistor-fault trip level can be adjusted using the
SE-MON330 software or via network communications.
See Section 6.1.
2.1.7 GEO-MAGNETIC FILTER
A low-frequency earth current can be caused by the
Earth’s magnetic field and from charged clouds passing
overhead during a thunderstorm. In some rare conditions,
this can cause a false resistor-fault trip. Enabling the geo-
magnetic filter and increasing the resistor-fault trip time
can help counteract these effects.
A trip time of 30 seconds is recommended when the
geo-magnetic filter is enabled.
The geo-magnetic filter is disabled by default, but can
be enabled using the SE-MON330 software or via
network communications.
2.2 CALIBRATION
The SE-330AU measures the resistance change of the
NER relative to the NER-resistance value determined at
the time of calibration. When the resistance change is
greater than a threshold amount (500 Ωfor 20-kΩ
systems, 2,500 Ωfor 100-kΩsystems), a resistor-fault trip
occurs. Calibrate the SE-330AU on new installations, if
the NER is changed, or if the sensing resistor is changed.
The CALIBRATION button is located behind the
access cover on the front panel, and it is recessed to
prevent inadvertent activation.
NOTE:Calibration must be performed with the
SE-330AU connected to the sensing resistor and NER of
the installed system.
NOTE:Where used, coupling components for lockout
earth-fault protection devices must be disconnected from
the supply during calibration.
To calibrate, press and hold the CALIBRATION button
until the green CALIBRATED LED turns off and returns
to on (if the LED is already off, press and hold until the
LED turns on). Calibration takes approximately two
seconds. If calibration is not successful, a resistor-fault
trip occurs, the RESISTOR FAULT TRIP LED will be
on, the CALIBRATED LED will be off, and the
DIAGNOSTIC LED will flash the calibration-error code.
See Section 2.8.
The SE-330AU may be calibrated remotely using
the SE-MON330 software with the USB interface or the
communications options.
If latching resistor fault (switch S4) is selected, the
calibration-error code flashes until RESET is pressed
even if the CALIBRATED LED is on.
The calibration value is stored in non-volatile memory.
2.3 CT DETECTION
The SE-330AU monitors the continuity of the CT
circuit. When an open CT circuit is detected for two
seconds, the SE-330AU will trip on earth fault and the
diagnostic LED will flash the CT-Detection-Error code.
See Section 2.8. The CT-Detection-Error code remains
until CT-circuit continuity is detected and RESET is
pressed. If supply voltage is cycled, earth-fault trip
indication is not reset but the CT-Detection-Error
indication is reset. CT-Detection-Error indication will
resume after two seconds if CT-circuit continuity is not
detected.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
2.4 TRIP INDICATION AND RESET
Red LED's and indication relays indicate earth-fault
and resistor-fault trips. The indication relays K2 (EF) and
K3 (RF) operate in fail-safe or non-fail-safe mode. The
default is non-fail-safe mode. In this mode, the relays are
energized when a fault occurs. The relay mode setting is
stored in non-volatie memlory and can be set using the
SE-MON330 software or network communications.
When a trip occurs with latching operation selected, the
SE-330AU remains tripped until reset with the front panel
button or the remote-reset input. See Sections 2.1.4.1 and
2.1.4.2. Terminals 15 and 16 are provided for remote
reset as shown in Fig. 3. The reset circuit responds only
to a momentary closure so that a jammed or shorted
button does not prevent a trip. The front-panel RESET
button is inoperative when terminal 15 is connected to
terminal 16. If non-latching operation is selected, trips
and corresponding indication automatically reset when the
fault clears. Resistor-fault-trip reset can take up to one
second.
The red DIAGNOSTIC LED annunciates latched
calibration error and remote trips. See Section 2.8.
When supply voltage is applied, the SE-330AU returns
to its state prior to loss of supply voltage. A resistor-fault
trip-memory trip can take up to three seconds after
SE-330AU power-up.
2.5 REMOTE OPERATION
Relays K2 and K3 can be used for remote indication,
and terminals 15 and 16 are provided for remote reset.
RK-332 Remote Indication and Reset components are
shown in Fig. 19. Connect them as shown in Fig. 3.
RK-332 components are not polarity sensitive.
Indication relays can be set to fail-safe or non-fail-safe
operation using the SE-MON330 software or network
communications. The default mode is non-fail-safe. In
non-fail-safe mode, relays energize on fault.
Network-enabled SE-330AU’s can be remotely tripped,
reset, and calibrated by the network master. The red
DIAGNOSTIC LED indicates a network-initiated trip.
See Section 2.8. Refer to the appropriate SE-330AU
communications manual.
2.6 RELAY K1 LED
The yellow RELAY K1 LED follows the state of relay
K1 and is on when K1 is energized (contact closed).
2.7 UNIT HEALTHY OUTPUT
UNIT HEALTHY relay K4 is energized when the
processor is operating. It can be ordered with N.O. or
N.C. contacts. See Section 7.
NOTE:The K4 output changes state momentarily during
a processor reset.
NOTE:K4-contact rating is 100 mA maximum.
2.8 DIAGNOSTIC LED
The DIAGNOSTIC LED is used to annunciate trips
without individual LED indication. The number of short
LED pulses between two long pulses indicates the cause
of the trip.
By default, both critical and non-critical diagnostic
flash codes are shown. Non-critical diagnostic codes
include SD Card status and USB Error status. All other
diagnostic codes are considered critical.
Starting with SE-330AU firmware version 2.60 and
SE-MON330 software version 3.8, the SE-330AU can be
configured to show only critical diagnostic codes. In this
configuration, non-critical diagnostic codes will not be
indicated with the DIAGNOSTIC LED.
Diagnostic messages are always visible with the SE-
MON330.
See Sections 4.2 and 5.
2.9 ANALOG OUTPUT
An isolated 4–20-mA output indicates NER current
with full-scale output corresponding to the CT rating. An
internal 24-Vdc supply allows the analog output to be
connected as a self-powered output. Power from an
external supply is required for loop-powered operation.
See Fig. 2. The PGA-0520 analog meter can be panel-
mounted to display the NER current. See Fig. 20 and
Section 7.
FIGURE 2. Analog-Output Connections.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
TABLE 1. TYPICAL VALUES FOR TRIPPING SYSTEMS
SYSTEM VOLTAGE
(VOLTS)
NEUTRAL-EARTHING
RESISTOR
EARTH-FAULT TRIP LEVEL
(AMPERES)
VN
TRIP
LEVEL
(VOLTS)
SENSING
RESISTOR
S5
LINE TO
LINE
LINE TO
NEUTRAL
CURRENT
(AMPERES)
RESISTANCE
(OHMS)
EFCT-X
(5-A
RATING)
SE-CS30-X
(30-A
RATING)
110 (3)
55
5
11
0.5
(1)
20
ER-600VC
20 kW
120 (3)
60
5
12
0.5
(1)
20
ER-600VC
20 kW
110
64
5
13
0.5
(1)
20
ER-600VC
20 kW
127
73
5
15
0.5
(1)
20
ER-600VC
20 kW
240 (3)
120
5
24
0.5
(1)
20
ER-600VC
20 kW
240
139
5
28
0.5
(1)
20
ER-600VC
20 kW
270
156
5
31
0.5
(1)
20
ER-600VC
20 kW
415
240
5
48
0.5
(1)
60
ER-600VC
20 kW
433
250
5
50
0.5
(1)
60
ER-600VC
20 kW
690
398
5
80
0.5
(1)
60
ER-600VC
20 kW
970
560
5
112
0.5
(1)
60
ER-5KV
20 kW
1,000
575
5
115
0.5
(1)
60
ER-5KV
20 kW
1,050
605
5
121
0.5
(1)
100
ER-5KV
20 kW
1,100
635
5
127
0.5
(1)
100
ER-5KV
20 kW
1,140
658
5
132
0.5
(1)
100
ER-5KV
20 kW
3,300
1,905
5
381
0.5
(1)
200
ER-5KV
20 kW
6,600
3,810
5
762
0.5
(1)
500
ER-15KV
100 kW
6,600
3,810
10
381
1.0
0.75
500
ER-15KV
100 kW
6,600
3,810
25
152
2.0
1.5
500
ER-15KV
100 kW
11,000
6,350
5
1,270
0.5
(1)
650
ER-15KV
100 kW
11,000
6,350
10
635
1.0
0.75
650
ER-15KV
100 kW
11,000
6,350
20
318
2.0
1.5
650
ER-15KV
100 kW
11,000
6,350
25
254
2.0
2.4
650
ER-15KV
100 kW
22,000
12,700
5
2,540
0.5
(1)
1,700
ER-25KV
100 kW
22,000
12,700
10
1,270
1.0
0.75
1,700
ER-25KV
100 kW
22,000
12,700
20
635
2.0
1.5
1,700
ER-25KV
100 kW
22,000
12,700
25
508
2.0
2.4
1,700
ER-25KV
100 kW
22,000
12,700
50
254
(2)
24
8,500
ER-25KV
100 kW
33,000
19,050
50
380
(2)
24
10,000
ER-35KV
100 kW
(1) Minimum setting is 0.75 A. Use EFCT-x for AS/NZS 2081:2002 compliance.
(2) Maximum setting is 5 A. AS/NZS 2081:2002 allows 25 A.
(3) Single phase, centre tap.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
3. INSTALLATION
3.1 SE-330AU
Outline and panel-cutout dimensions for the SE-330AU
are shown in Fig. 4. To panel mount the SE-330AU,
insert it through the panel cutout and secure it with the
four included 8-32 locknuts and flat washers. If an
optional SE-IP65CVR-G Hinged Cover is used, follow
the included installation instructions. See Figs 6 and 7.
All connections to the SE-330AU are made with
plug-in, wire-clamping terminal blocks. Each plug-in
terminal block can be secured to the SE-330AU by two
captive screws for reliable connections.
Outline dimensions and mounting details for surface
mounting the SE-330AU are shown in Fig. 5. Fasten the
optional SE-330-SMA Surface-Mount Adapter to the
mounting surface and make connections to the adapter
terminal blocks. Follow Fig. 5 instructions to mount or
remove the SE-330AU.
Connect terminal 7 (G) to earth and connect terminal
6 (R) to the sensing-resistor R terminal.
Use terminal 1 (L1) as the line terminal on ac systems,
or the positive terminal on dc systems. Use terminal 2
(L2/N) as the neutral terminal on ac systems or the
negative terminal on dc systems. Connect terminal 3 ( )
to earth.
NOTE: Disconnect terminal 1 (L1) and terminal 2 (L2/N)
before performing dielectric strength testing of the control
panel.
NOTE: Connections to terminals 4 (SPG) and 5 (SPGA)
are not required when using the SE-330AU hardware
revision 10 and higher. However, it is recommended to
connect terminal 4 to terminal 5 to maintain backwards
compatibility with the older SE-330AU series (hardware
revision 01 and lower).
3.2 SENSING RESISTOR
Outline and mounting details for the ER-600VC,
ER-5KV, ER-5WP, ER-15KV, ER-25KV, and ER-35KV
sensing resistors are shown in Figs. 8, 11, 12, 13, 14 and 15.
Install the NER and the sensing resistor near the transformer
or generator. An optional SE-MRE-600 Moisture Resistant
Enclosure is available for applications which may expose an
ER-600VC to moisture. See Figs 9 and 10. The weather-
protected ER-5WP shown in Fig. 12 is an ER-5KV with
moisture-resistant terminal covers. Use an ER-5WP in
applications in which it might be exposed to moisture. The
ER-15KV, ER-25KV, and ER-35KV include moisture-
resistant terminal covers. Use suitable water-tight fittings.
Connect terminal G to earth. Pass the sensing-resistor-to-
neutral conductor and the NER-to-neutral conductor
through the earth-fault-CT window as shown in Fig. 3.
Separately connect sensing-resistor terminal N and the NER
to the neutral to include neutral connections in the
monitored loop. Alternatively, if the NER connection to
system neutral need not be monitored, connect terminal N to
the NER neutral terminal.
If an earth fault in the sensing-resistor conductor is
unlikely, a minimal loss of protection will result if it does
not pass through the earth-fault-CT window. See Fig. 3.
NOTE:Voltage at terminal N rises to line-to-neutral voltage
when an earth fault occurs. The same clearances are
required for sensing resistors as for NER’s.
NOTE: A parallel earth path created by moisture can
result in a false resistor-fault trip. Moisture sources
include wind-driven rain or snow, and condensation.
Sensing-resistor terminal R and its connection to SE-
330AU terminal R, including interposing terminal blocks,
must remain dry.
NOTE:The neutral-to-sensing-resistor-terminal-N connection
is not a neutral conductor. Since current through this
conductor is always less than 250 mA, a 1.5 mm2
conductor insulated to the system voltage is more than
sufficient.
NOTE: For outdoor installations, sensing resistors must be
in an IP14 enclosure.
3.3 EARTH-FAULT CT
Select and install an earth-fault CT that will provide the
desired trip level. Typically, the CT-primary rating
should be approximately equal to the NER let-through-
current rating. This provides an appropriate EF TRIP
LEVEL setting range and analog-output scaling. The
primary rating of the EFCT-x is 5 A and the primary rating
of the SE-CS30-x is 30 A. See Sections 2.1.2 and 2.9.
Outline and mounting details for the sensitive EFCT-x
and SE-CS30-x current sensors are shown in Figs. 16, 17,
and 18. Earth-fault-CT connections and the typical earth-
fault-CT location are shown in Fig. 3. If an earth fault in
the NER is unlikely, a minimal loss of protection will
result if the earth-fault CT monitors the NER connection
to earth rather than its connection to neutral.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 3. SE-330AU Connection Diagram.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 4. SE-330AU Outline and Panel-Mounting Details.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 5. SE-330AU Outline and Surface-Mounting Details.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 6. SE-IP65CVR-G Weatherproof Cover Outline.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 7. SE-IP65CVR-G Weatherproof Cover Installation.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 8. ER-600VC Sensing Resistor.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 9. SE-MRE-600 Moisture Resistant Enclosure.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 10. ER-600VC Installed in SE-MRE-600.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 11. ER-5KV Sensing Resistor.

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SE-330AU Neutral-Earthing-Resistor Monitor Rev. 4-I-101817
FIGURE 12. ER-5WP Sensing Resistor.