Description
2.5 Protection functions
3VA molded case circuit breakers with UL and IEC certification
70 Manual, 01/2019, L1V30435333-01
The ID letter for ground-fault protection is "G" (stands for "ground fault").
The G protection detects residual currents between phases and grounded, electrically
conductive parts. The ground-fault protection function responds if the ground fault current
exceeds the set tripping current I
g
for the set delay period t
g
.
Like for the short-time delayed short-circuit protection, the delay time of the ground fault
protection can be set as either a current-independent or a current-dependent (I
2
t) value,
dependent on the trip unit options.
Special variants with ground-fault alarm-only are available for the 3VA UL molded case
circuit breakers. These are the 3VA6 molded case circuit breakers with ETUs 556 and 856.
When a ground-fault current is detected, the breaker does not trip.
Rather, only an indication is provided via the ETU display and, if desired, via a
programmable digital output on the External Function Box (EFB) and/or through
communications. This allows the system to remain in operation.
On 4-pole molded case circuit breakers and 3-pole molded case circuit breakers with
external current transformer for the N conductor, the G protection calculates the vector sum
of the currents of the three phases and the neutral conductor. The G release trips the
molded case circuit breaker, or an alarm is issued via the communication system if the trip
unit is alarm-only, if the rms value of this vector sum exceeds the set response threshold I
g
for the set delay time t
g
.
Measurement method 1: Vectorial summation (residual) current
Ground-fault detection in balanced systems
3-pole molded case circuit breaker in balanced systems:
Trip unit variants
● ETUs 3-series: ETU330 (LIG)
● ETUs 5-series: ETU556 (LSIG alarm), ETU560 (LSIG)
● ETUs 8-series: ETU830 (LIG), ETU856 (LSIG alarm), ETU860 (LSIG)
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