3714 Kinnear Place
Saskatoon, Saskatchewan
Canada
S7P 0A6
Ph: (306) 373-5505
Fx: (306) 374-2245 www.startco.ca
SE-502 MANUAL
GROUND-FAULT GROUND-CONTINUITY DETECTOR
April 25, 2012
REVISION 0
Copyright © 2012 by Littelfuse Startco
All rights reserved.
Publication: SE-502-M
Document: S95-C502-00000
Printed in Canada.
SE-502 Ground-Fault Ground-Continuity Detector
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SE-502 Ground-Fault Ground-Continuity Detector
PREFACE
Current flowing to ground has only two paths—it can flow to
ground through a ground fault, and it can flow to ground
through distributed capacitance. Current flowing to ground
through distributed capacitance can cause sympathetic tripping
during a ground fault and its unbalance can cause tripping
during normal operation. These trips are not to be confused
with false trips that occur when poorly designed ground-faultdetection systems respond to anything other than zero-sequence
current at the fundamental frequency. All of these trips are
nuisance trips. If nuisance trips are frequent enough to
interfere with production, there is a danger that the protection
will be defeated.
A sympathetic ground-fault trip is a trip that occurs on an
unfaulted portion of a system when a ground fault occurs
elsewhere in the system. Sympathetic tripping can occur if
capacitive current flowing to a ground-fault from an unfaulted
portion of the system is larger than the ground-fault trip level.
Consequently, coordination using conventional ground-fault
relays and zero-sequence-current detectors requires the groundfault trip level to be larger than the charging current of the
largest protected portion of the system. Since this trip level is
usually larger than the unbalanced capacitive current flowing to
ground due to unbalanced voltage and/or capacitance to
ground, a coordinated, well-designed, ground-fault-protection
system will not have nuisance trips.
In small systems or systems with one ground-fault relay,
sympathetic tripping is not a concern and nuisance tripping can
be avoided if the ground-fault trip level is larger than the
unbalanced capacitive current flowing to ground.
Unfortunately, this level is usually above the trip levels
required for single-phase Class-A GFCI’s and personnel
protection must be achieved by other means. In distribution
and utilization systems, protection is achieved by controlling
touch and step potentials and by limiting the voltage to which
exposed metal parts can rise during a ground fault—no attempt
is made to trip at the GFCI levels mandated for small singlephase loads. In spite of the fact that GFCI levels were never
intended for three-phase systems, attempts are often made to
achieve these trip levels on equipment such as submersible
pumps.
A special problem exists with respect to portable generators.
Most electrical codes require portable generators to be
grounded with ground rods or electrodes; however, location
and conditions can make this difficult to achieve. This problem
has been recognized by Ontario Hydro—Electrical Inspection,
Metro Territory. On September 28, 1998, Ontario Hydro
issued guidelines to Inspectors and the entertainment industry
to assist them to achieve safe electrical installations. These
guidelines allow a ground (other than an approved electrode) to
be used if it is verified with a ground proving device. Also, in
1997 the Construction Safety Association of Ontario (CSAO)
published a report titled The Use of Ground Fault Circuit
Interrupters on Portable Generators. This report outlines
conditions under which personnel protection is not achieved
with GFCI’s.
The SE-502 Ground-Fault Ground-Continuity Detector
provides a solution to the problem of personnel protection for
portable generators. It also has application in utilization
systems requiring a lockout that will not allow a faulted system
Pub. SE-502-M, April 25, 2012.
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to be energized. Consider the following:
 Since capacitance to ground causes nuisance-tripping
levels in conventional systems to be larger than Class-A
GFCI trip levels, a technique that ignores capacitive
current to ground is required if Class-A GFCI trip levels
are to be achieved without nuisance tripping. The SE-502
accomplishes this by using a dc signal to measure
resistance to ground of the entire system.
The
disadvantage of this technique is that it will not detect
current through a person contacting a phase conductor with
a series capacitor. We are faced with a conundrum—it is
impossible to build a protective relay that both ignores and
detects capacitive current. Since the probability of contact
through a capacitor is much smaller than the probability of
direct or resistive contact, the SE-502 reduces risk to
personnel by providing protection in the most probable
occurrences that could result in electrocution.
 It is a common misconception that conventional GFCI’s
limit ground-fault current to 5 or 30 mA. They do not.
Ground-fault current is limited only by the system
impedance until the trip occurs. The SE-502 limits
ground-fault current to a maximum value of 100 mA.
 A very positive consequence of the 100-mA limit is that
the arc-flash hazard on the first ground fault is eliminated.
 The SE-502 confirms an acceptable ground so that a
ground-fault trip is assured when a ground fault occurs.
 Ground-fault operation can be easily and safely tested on a
de-energized system.
 The SE-502 resistance grounds the system; ensure local
electrical codes permit the use of resistance grounding with
line-to-neutral loads. Canadian Electrical Code Section
10-1102 specifically allows, and lists provisions for, lineto-neutral loads on resistance-grounded systems.
SE-502 Ground-Fault Ground-Continuity Detector
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SE-502 Ground-Fault Ground-Continuity Detector
TABLE OF CONTENTS
PAGE
Preface ............................................................................ i
1.
General .......................................................................... 1
2.
2.1
2.3
Operation ....................................................................... 1
Configuration-Switch Settings ..................................... 1
2.1.1 Trip Relay Operating Mode ............................ 1
2.1.2 Ground-Continuity Trip .................................. 1
Front-Panel Indication .................................................. 1
2.2.1 Ground Fault .................................................... 1
2.2.2 Ground Continuity........................................... 1
2.2.3 Power ............................................................... 2
2.2.4 Open Neutral.................................................... 2
2.2.5 Diagnostic Error .............................................. 2
Reset .............................................................................. 2
3.
Installation ..................................................................... 2
4.
Technical Specifications ............................................... 2
5.
Warranty........................................................................ 2
2.2
Pub. SE-502-M, April 25, 2012.
LIST OF FIGURES
1
2
PAGE
SE-502 Outline and Mounting Details ......................... 3
SE-502 Typical Application ......................................... 4
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.
SE-502 Ground-Fault Ground-Continuity Detector
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SE-502 Ground-Fault Ground-Continuity Detector
Page 1
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1. GENERAL
2. OPERATION
The SE-502 is a microprocessor-based, ground-fault and
ground-continuity detector that provides Class-A GFCI trip
levels and trip times for a three-phase 120/208-V portable
generator. All operating conditions are clearly indicated and
Form C contacts are provided for the main breaker’s trip
circuit. Two Form C contacts are also provided for remote
ground-fault and ground-continuity indication.
All
specifications apply over an industrial temperature range at
high humidity, and the SE-502 is designed to meet the IEEE
surge-withstand-capability tests (oscillatory and fast
transient) for protective relays and relay systems.
The SE-502’s ground-fault circuit has an internal neutralgrounding resistor (NGR) that limits ground-fault current to
100 mA. This eliminates the flash hazard, and susceptibility
to nuisance tripping is reduced as trip times less than 100 ms
are not required to achieve Class-A GFCI performance. The
SE-502 impresses a small dc voltage on the neutral of the
generator to measure the resistance to ground of the entire
system connected to the load side of the generator’s main
breaker. If resistance to ground is less than 24 k (5 mA @
120 V), the SE-502 will trip the main breaker in less than
Class-A times and it will not allow the main breaker to close
until resistance to ground is greater than 24 k. LED
indication and a relay for remote indication of a ground fault
are diagnostic tools that allow a ground fault to be easily
located on a de-energized system. When a faulted section is
disconnected from the system by breakers or by couplers,
the SE-502 will indicate that no fault exists and it will allow
the main breaker to be set.
The SE-502 is designed to be used in a tripping system.
If a system remains energized with a ground fault, the
SE-502 will reduce NGR current if NGR temperature
approaches its thermal limit.
The SE-502’s ground-continuity circuit uses a sense lead
connected to a probable ground to confirm that the electrode
chosen for the system ground is an acceptable ground.
Ground-electrode-loop resistance must be less than 25  for
the circuit to confirm the ground. LED indication and a
relay for remote indication allow probable grounds to be
easily tested for acceptability. If the ground-continuity-trip
switch is in the ENABLE position, the resistance of the
ground-electrode loop will be continuously monitored and it
will trip the main breaker if the loop resistance increases
above 50 .
The SE-502 neutral-continuity circuit uses a sense lead
connected to the system neutral to continuously monitor
continuity of the neutral circuit. A loss of continuity initiates
a trip, which is indicated with an LED.
2.1 CONFIGURATION-SWITCH SETTINGS
See Fig. 1.
2.1.1 TRIP RELAY OPERATING MODE
Switches 1 and 2 are used to set the operating mode of the
trip relay. In the non-fail-safe mode, the trip relay is
energized when a trip occurs. In the fail-safe mode, the trip
relay is energized when the circuits are not tripped. Nonfail-safe operation requires both switches to be in the nonfail-safe position.
Switches 1 and 2 do not affect operation of the groundfault and ground-continuity annunciation relays.
Pub. SE-502-M, April 25, 2012.
2.1.2 GROUND-CONTINUITY TRIP
Switch 3 is used to ENABLE or DISABLE groundcontinuity trip. In the DISABLE position, a loss of ground
continuity will not cause a trip. In the ENABLE position,
ground-continuity loop resistance must increase above 50 
for 1 s to cause a ground-continuity trip. A groundcontinuity trip will not reset unless loop resistance is less
than 25 . In both switch positions, ground continuity is
indicated and the remote-indication relay is energized when
ground-electrode-loop resistance is less than 25 .
2.2 FRONT-PANEL INDICATION
2.2.1 GROUND FAULT
The red LED labeled TRIP indicates a ground-fault
circuit trip. See Section 2.3.
The yellow LED labeled PRESENT indicates that a
ground fault is present. The ground-fault annunciation relay
is not energized.
The green LED labeled CLEAR indicates that a ground
fault is not present. The ground-fault annunciation relay is
energized.
2.2.2 GROUND CONTINUITY
The red LED labeled TRIP indicates a ground-continuitycircuit trip. A trip will remain latched until the groundelectrode-loop resistance is less than 25  and a reset is
performed. See Section 2.3.
The yellow LED labeled NO indicates an unacceptable
ground-electrode-loop resistance. The ground-continuity
annunciation relay is not energized and a groundcontinuity trip will not reset.
The green LED labeled YES indicates an acceptable
ground-electrode-loop resistance. The ground-continuity
annunciation relay is energized and a ground-continuity trip
can be reset.
SE-502 Ground-Fault Ground-Continuity Detector
2.2.3 POWER
The green LED labeled POWER indicates presence of the
supply voltage.
2.2.4 OPEN NEUTRAL
The red LED labeled OPEN NEUTRAL indicates an
open-neutral trip. An open-neutral trip is caused by a
lack of continuity between NEUTRAL SENSE terminal 8
and NEUTRAL terminals 1 and 2. See Fig. 2.
Some lamp-ballast-ground tests may cause a nuisance
open-neutral trip.
2.2.5 DIAGNOSTIC ERROR
The red LED labeled DIAGNOSTIC ERROR indicates a
diagnostic-error trip. Press RESET or cycle supply voltage.
If problem persists, contact Littelfuse Startco.
A flashing LED indicates that the NGR has reached its
thermal limit. Clear the ground fault, allow the SE-502 to
cool, and press RESET.
2.3 RESET
When a trip occurs, the trip remains latched until the
RESET switch is pressed, the remote-reset terminals (12 and
13) are shorted, or the supply voltage is cycled. The reset
circuit responds only to a momentary closure so that a
jammed or shorted switch will not maintain a reset signal.
3. INSTALLATION
An SE-502 can be surface or DIN-rail mounted. See
Fig. 1.
Connect the SE-502 as shown in Fig. 2. Ensure that the
generator neutral is not internally grounded. Remove the
connection to terminal 18 for dielectric-strength testing—all
inputs and outputs have ANSI/IEEE C37.90 surgeprotection circuits that conduct above 300 Vac.
4. TECHNICAL SPECIFICATIONS
Supply:
120 Vac (+15%, -30%), 50/60 Hz, 3.5 VA
Dimensions:
Height .................................... 75 mm (3.0")
Width ..................................... 100 mm (4.0")
Depth ..................................... 113 mm (4.4")
Shipping Weight ........................... 0.68 kg (1.5 lb.)
Ground-Fault Circuit:
Trip Level .............................. 5 ± 0.9 mA
Trip Time .............................. (Class A GFCI - 25 ms) max.
5–15 mA ........................ 250 ms max.
15–100 mA .................... 75 ms max. (average of 10
or more measurements)
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NGR ...................................... 1440 
Thermally Protected
Ground-Continuity Circuit:
Continuity Indication ............ < 25 
Trip Resistance ..................... > 50 
Trip Time .............................. 1 ± 0.1 s
Neutral-Sense Circuit:
Trip Time .............................. 5 ± 0.1 s
Reset ............................................. Front-Panel Switch and
Remote N.O. Momentary
Contact
Output Relays:
Contact Rating ..................... 8 A Resistive,
250 Vac/30 Vdc
Contact Configuration ......... Form C
Trip Relay
Operating Mode ................ Fail Safe or Non Fail Safe
Annunciation Relays
Operating Mode ................ Fail Safe
Environment:
Operating Temperature ........ -40°C to 70°C
Storage Temperature ............ -55°C to 80°C
Humidity ............................... 85% Non Condensing
Surge Withstand ........................... ANSI/IEEE 37.90.1-1989
(Oscillatory and Fast
Transient)
5. WARRANTY
The SE-502 Ground-Fault Ground-Continuity Detector is
warranted to be free from defects in material and
workmanship for a period of five years from the date of
purchase.
Littelfuse Startco will (at Littelfuse Startco’s option)
repair, replace, or refund the original purchase price of an
SE-502 that is determined by Littelfuse Startco to be
defective if it is returned to the factory, freight prepaid,
within the warranty period. This warranty does not apply to
repairs required as a result of misuse, negligence, an
accident, improper installation, tampering, or insufficient
care. Littelfuse Startco does not warrant products repaired
or modified by non-Littelfuse Startco personnel.
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Rev. 0
SE-502 Ground-Fault Ground-Continuity Detector
GROUND-CONTINUITY-TRIP ENABLE
FAIL-SAFE
3
2
1
GROUND-CONTINUITY-TRIP DISABLE
NON-FAIL SAFE
NOTES:
1. DIMENSIONS IN MILLIMETRES (INCHES).
N
1
NEUTRAL CONTINUITY RESET
SENSE SENSE
G
2
3
4
5
6
7
8
9
10
11
2. MOUNTING SCREWS: M4 x 13 OR 8-32 x 0.50.
12 13 14 15
3. OVERALL DIMENSION WHEN MOUNTED ON
DIN EN50022 35 mm x 7.5 mm TOP-HAT RAIL.
TOP
99.80
(3.93)
75.0
(2.95)
113.0 (NOTE 3)
(4.45)
FRONT
SIDE
7.4
61.2
(2.41)
75.0
(2.95)
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
GROUND
GROUND
L2
FAULT
CONTINUITY
TRIP
/ S
P
L1 N G
(0.29)
99.80
(3.93)
85.0
(3.35)
MOUNTING DETAIL
FIGURE 1. SE-502 Outline and Mounting Details.
Pub. SE-502-M, April 25, 2012.
6.9
(0.27)
BOTTOM
SE-502 Ground-Fault Ground-Continuity Detector
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Rev. 0
GENERATOR
120/208 V
CABLE
120-V
LOADS
N
16
L1
L2/N
21
17
TRIP
20
TRIP
22
GF
23
GF
25
UV
G
24
UV ENERGIZED
R
GF INDICATOR
27
GC
26
G
GC
28
GC INDICATOR
REMOTE RESET
12
13
1
2
RESET
NEUTRAL
8
SENSE
GROUND
NEUTRAL
5
6
SE-502
18
19
SPG
CONTINUITY
10
SENSE
GROUND
ELECTRODE
SENSE LEAD
TO ALTERNATE
GROUND
FIGURE 2. SE-502 Typical Application.
Pub. SE-502-M, April 25, 2012.
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