Siemens RL Series, Instructions Manual

Page: 43 / 76

Fuse Functions
Current Limiting Fuses
Current limiting (Cl) fuses are used to increase the
interrupting capacity beyond that of the breaker alone,
or to limit the fault "let-thru" current downstream of the
fuse. The CL fuses used with the RL series of circuit
breakers are s p ec ial purpose fuses having NEMA
Class "J" or Class "L" characteristics with an
interrupting capacity of 200,000 Amperes RMS
Symmetrical.
When fuse replacement is required, use only fuses as
shown on Siemens drawing 7 1 -1 42-200, having the
same ratings as supplied with the circuit breaker.
Different fuses may not properly mount on the breaker
and may have different protective characteristics.
The current limiting fuses for the larger frame sizes
(RLF-3200, RLF-4000 and RLF-5000) mount on a
separate fuse Drawout assembly. For complete
description , see 'Fuse Carriage', beginning on
Page 22.
Open Fuse Trip Device
. AWARNING
·
Hazardous voltage.
Can
cause
death, serious
personal injury, elec­
trical shock
bums, or property damage.
Lme
voltage
may be present inside trigger
fuse
assembly.
Do
not remove trigger fuse cover when
c�rcuit breake�
e1
fuse carriage is in the
CONNECT
poSitiOn
The Open Fuse Trip mechanism has three functions:
I
. To trip the circuit breaker mechanically when a CL
fuse has interrupted
2. To indicate which phase CL fuse has interrupted.
The plunger of the trigger fuse (1 3), indicates visually
which phase CL fuse has interrupted.
3. To retain the breaker in the trip free position until
the trigger fuse is replaced.
Each trigger fuse is wired in parallel with one of the CL
fuses. When the CL fuse interrupts, its associated
trigger fuse also opens, releasing a plunger and
precompressed spring contained in the trigger fuse
housing.
See F i g u
r
e 1 1 . On the integrally fused
breakers (RLF-800 through RLF-2000), this plunger
operates arm (3) which moves the latch (1 2), releasing
the spring-loaded lever (4). This rotates circuit breaker
trip flap link (7). This trips the circuit breaker and holds
the circuit breaker
in
the mechanical trip-free position.
20
On large frame size circuit breakers (RLF-3200 through
RLF-5000) supplied with a separate fuse carriage, the
trigger fuses are mounted on the fuse carriage, and a re
used for visual identification of the faulted phase.
Tripping of the breaker is accomplished through a
power supply connected across the main fuses of the
fuse carriage. The voltage from this supply is applied
through the secondary control wiring to the coil of a
solenoid mounted open fuse trip device on the circuit
breaker. The plunger of the solenoid operates arm (3).
The balance of the operation is the same as for the
trigger fuse o perated device.
The circuit breaker will remain trip free (cannot be
closed} until the trigger fuse has been replaced and the
associated trip mechanism reset lever (4) has been
manually reset (pushed up).
To remove the trigger fuse, remove screws ( 1 5},
remove plastic cover (5}, then the trigger fuse.
To install the trigger fuse, reverse the above procedure.
NOTE: The trigger fuse (13) must be inserted with
the plunger facing anm (6). The gap dimension of
0.03"
(0.8mm) maximum must be maintained for
each fuse. Be sure to replace both the trigger fuse
a n d its corresponding CL fuse before the breaker is
r e s et
.
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