Fuse Application and Selection Data
Siemens Type VBII Safety Switch
Siemens enclosed safety switches are
designed for fuse versatility. Although
Siemens is not a manufacturer of fuses,
once the type of fuse needed for a
particular application is determined, it's
easy to select an appropriate switch.
One-time fuses are standard for use in
situations calling for 1200 amperes or
less with maximum voltages for 250 or
600 volts. Specially designed, current-
carrying links are connected to contact
pieces at the ends of the enclosure.
When an overload occurs, the circuit
quickly opens and the arc is quenched
by granular insulating material that
surrounds the current carrying links.
Available in all classes.
The proper fuse type for the application
is selected using the following
• Voltage requirements
• Conductor ampacity
• Horsepower requirements
• Maximum available RMS
• UL fuse class when specified
Current Limiting Fuses
This design offers the highest degree of
circuit protection among fuses. Inside,
usually copper or silver alloy links are
embedded in pure quartz sand between
heavy copper end blocks. The special
design is fast-acting and interrupts
during the first half-cycle of a fault.
This causes a limitation of both fault-
peak current and let-through
Available in Classes J, L, R and T.
The compatible fusible safety switch is
selected following these parameters:
• System voltage requirements
• Fuse amp ratings
• Available fault current
• UL fuse class
• Environmental conditions
• Number of poles required
Dual-element Time-delay Fuses
Dual-element fuses may have time-
delay designation since these fuses
employ two distinctly separate types
of elements. One provides overload
protection with time delay. (UL states
that time delay means having a
10-second operating delay at 500
percent of fuse label rating.) The
second provides short circuit protection
similar to a single-element fuse.
Dual-element fuses are most frequently
used on motor loads.