Startco Engineering Ltd. Page 1
SE-701 Ground-Fault Monitor Rev. 6
Pub. SE-701-M, January 18, 2008.
1. INTRODUCTION
1.1 GENERAL
The SE-701 is a microprocessor-based ground-fault
monitor for resistance-grounded and solidly grounded
systems. It is uniquely suited for use on systems with
significant harmonic content. Its output relay can operate
in the fail-safe or non-fail-safe mode for undervoltage or
shunt-trip applications. The SE-701 has one output relay
with isolated normally open and normally closed contacts
for use in independent control circuits. Additional
features include LED trip, power, and inhibit indication,
autoreset or latching trips with front-panel and remote
reset, trip memory, test switch, self diagnostics, 0- to 5-V
analog output, inputs for standard and sensitive ground-
fault current transformers, CT verification for sensitive
current transformers, digital selector switches, switch-
selectable algorithms for fixed-frequency or variable-
frequency applications, and an inhibit that can be enabled
to prevent the output relay from operating during a high-
current ground fault.
Ground-fault current is sensed by a core-balance zero-
sequence current transformer (CT). The trip level of the
ground-fault circuit is switch selectable in 1% increments
from 1 to 99% of the CT-primary rating.
1.2 CURRENT-TRANSFORMER SELECTION
An SE-701 has inputs for 1-, 5-A, and sensitive 50-mA-
secondary CT’s. Choose a CT that provides the required
ground-fault-trip range.
For ground-fault detection, the ground-fault trip level
must be substantially below the prospective ground-fault
current. In a solidly grounded system, prospective ground-
fault current is similar to phase-fault current. In a resistance-
grounded system, prospective ground-fault current is
defined by the neutral-grounding-resistor let-through-current
rating.
In a solidly grounded system, protection against arcing
ground faults requires a ground-fault CT that will detect
low-level fault current but not saturate up to the operating
value of the system overcurrent protection. In general,
immunity to saturation is proportional to CT mass.
To eliminate nuisance tripping, surge current must not
saturate the CT.
For low-level ground-fault protection use an EFCT-1,
EFCT-2, or EFCT-26 sensitive earth-fault CT with a 5-A-
primary rating. However, protection at this level might not
be possible because of high surge current or prospective
ground-fault current.
For CT-selection assistance, see Technical Information
11.1 available at www.startco.ca
2. OPERATION
2.1 CONFIGURATION-SWITCH SETTINGS
See Fig. 1.
2.1.1 RELAY OPERATING MODE
Switch 1 is used to set the operating mode of the output
relay. In the fail-safe mode, the output relay energizes
when the ground-fault circuit is not tripped. In the fail-
safe mode, non-volatile memory retains the trip status of
the SE-701. If tripped, and the supply voltage is cycled,
the SE-701 will remain tripped, with the trip relay
de-energized and the TRIP LED on, until reset.
In the non-fail-safe mode, the output relay energizes
when a ground-fault trip occurs. In the non-fail-safe
mode, trip status is not retained in non-volatile memory.
2.1.2 TRIP INHIBIT
Switch 2 is used to select Class I or Class II operation.
In the OFF position, high-current trip inhibit is off for
Class I operation. In the ON position, high-current inhibit
is on for Class II operation. If high-current trip inhibit is
on and ground-fault current escalates above eleven times
the CT-primary rating before the ground-fault circuit
trips, the output relay will not operate until ground-fault
current falls below eight times the CT-primary rating.
This feature allows overcurrent protection to operate in
applications where the ground-fault current can be larger
than the interrupting capacity of the device tripped by the
SE-701.
2.1.3 CT VERIFICATION
Switch 3 is used to enable CT verification with an
EFCT-series CT. In the ON position, a trip will occur if
the CT is disconnected. Switch 3 must be in the OFF
position when an EFCT-series CT is not used.
2.1.4 FILTER SELECTION
Switch 4 is used to select the filtering algorithm for a
fixed-frequency (50/60 Hz) or variable-frequency
application. The FIXED FREQUENCY setting uses a
DFT filter that allows lower trip levels to be used by
rejecting harmonics that can cause nuisance tripping.
The VARIABLE FREQUENCY setting uses a peak-
detection algorithm with a wider band width for fault
detection in variable-frequency drive applications.
2.1.5 RESET MODE
Switch 5 is used to select autoreset or latching trips.
See Section 2.2.3.
