Application And Configuration Of Fused Circuit Breakers - Siemens UL 1066 Operating Instructions Manual

5.3.1

Application and configuration of fused circuit breakers

5.3.1.1 Integrally fused and non-integrally fused circuit breakers
Frame size II (800 A through 2000 A) circuit breakers are equipped with fuses, which are fitted directly to the circuit breaker.
Due to size and heat constraints, the frame size III (3200 A through 5000 A frames) are not integrally fused. The fuses are mounted in a
separate fuse carriage which has the same outer dimensions as the circuit breaker and are connected in series with the associated circuit
breaker. The fuse carriage and frame size III fuse switch breaker system can be mounted in the same vertical section, or adjacent to one
another, but it is important that the interconnecting bus be kept as short as possible. The suitability of the design must be verified by type
testing.
Siemens fused circuit breakers are not sensitive to the infeed direction. The circuit breakers (or the combination of circuit breaker and fuse
carriage) can be fed from either the upper or the lower terminals.
5.3.1.2 Open fuse lockout
Every Siemens fused circuit breakers (or fused switch) is equipped with an open fuse lockout (OFLO). The purpose of the OFLO device is to
open the circuit breaker (or switch) and hold the device in the trip-free position until after the primary fuses have been replaced.
For frame size III fused devices, additional control wiring is required to interconnect the OFLO device within the fuse carriage and the OFLO
device within the circuit breaker (switch)..
Equipment damage.
Incorrect connection of the open-fuse lockout will prevent the circuit breaker from tripping when a fuse in the fuse carriage
responds. Polarity must be observed.
Connect the OFLO as shown below.
5 – 8
NOTICE
Fuse carriage
X9-4 X9-3
Fused circuit breaker