Specification

Siemens Type VBII Safety Switch
53
Switch
Rating I
2
t Rating Ip Rating
Ampere (Amp2 x sec.) (Amps)
30 50,000 14,000
60 200,000 26,000
100 500,000 32,000
200 2,000,000 50,000
400 6,000,000 75,000
600 12,000,000 100,000
800 10,000,000 80,000
1200 15,000,000 120,000
Multiple-Voltage
Horsepower Ratings
A switch may have additional standard
and maximum horse-power ratings for
different voltages. A switch that is
horsepower rated at 240V AC or 250V
DC may also have horsepower ratings
for motors on 120V AC or 125V DC
circuits.
Multipole Horsepower Ratings
A switch may have horsepower ratings
applicable to the same current and
voltage ratings but with fewer poles
if the switch is investigated and found
suitable for the assigned rating.
Short-circuit Withstandability
UL test procedures for switches and
fuses have been expanded to provide
realistic standards of performance
with respect to clearing high-level
fault currents.
These revised standards deal with the
control of destructive energy in the
shorted circuit. Two types of potential
damage are characteristic of high-level
short-circuits: mechanical and thermal.
Mechanical damage is caused by the
electromagnetic force surrounding
conductors; thermal damage is the
result of excessive current during
the fault-clearing time.
Short Circuit Rating (RMS Symmetrical Amperes)
Fuse Rating Fuse Class General Duty Heavy Duty
Fusible Plug 10,000 –
H or cir
cuit breaker 10,000 10,000
K 10,000 10,000
J 100,000 200,000
R 100,000 200,000
T 100,000 200,000
L –– 200,000
Non-Fusible ➀ H or circuit breaker 10,000 10,000
K 10,000 10,000
J 100,000 200,000
➁
R 100,000 200,000
➁
L –– 200,000
Short-circuit Withstand Ratings
I
2
t and Ip Ratings
The UL fuse standard defines maximum
instantaneous peak let-through current
(lp) and maximum destructive energy
let-through (I2t) for each fuse (except
Class H). Applications of fuses and
safety switches on systems having
more than 10,000A are available.
Short circuits require selections of
the proper UL-listed fuses and switches
capable of withstanding I2t let-
throughs. See chart below for with-
stand ratings on Siemens switches.
I2t Rated
Suitability tests for service with Class
H, R, J, L and T fuses have been
conducted. Representative switches
with test fuses connected in series
with each switch were subjected to
I2t let-through values in excess of
the capacities of the largest fuses
acceptable by the switches.
To pass the test, the switch must
remain operable after being
closed into a high-amp available
short-circuit current. The test fuse
is sized so that higher levels of
let-through current and energy will
be reached than would ever occur
during normal usage in the field.
See the chart below for I2t ratings
on Siemens switches.
➀ With fuses or circuit breaker in series with switch. Fuse or circuit breaker ampere rating cannot exceed switch ampere rating.
➁ 60A compact switches are rated 100,000 with 60A max.
Class J or R fuses in series with switch.