S-9
Technical Information
Specifications are subject to change without notice. www.hubbell.com/bryant/en/
Prior to 1950, Underwriters Laboratories, Inc. listed only
AC/DC general use switches. These switches were designed
with oveS-center, snap-acting mechanisms which opened
the circuit by widely separating the contacts at a high speed.
This was necessary because the switches were tested on DC
which has a steady-state voltage.
With the introduction of AC only general use switches, it was
unnecessary to have the high-powered, oveS-center, snap-
acting mechanisms because the contacts did not have to be
widely separated at high speed.
Bryant introduced, in the mid 1930’s, the first AC only range
switch. The experience gained in this development indicated
the ideal AC switch should have a positive closing and a slow
limited opening.
Positive closing is the closing of the contacts without bounce
or chatter, which can occur due to the inertia of a high-speed
closing of the contacts.
This is important, especially on the tungsten lamp load where,
due to the low resistance of tungsten filament, an inrush
current from 8 to 16 times the lighted (high resistance) rated
current occurs. This inrush occurs in the first quarter cycle,
1/240 of a second, or when the contacts first close and would
be bouncing (rapidly opening and closing of the circuit).
Contact bouncing, at high current, could cause considerable
arcing which would dissipate the contact material and result in
welding of the contacts.
Slow limited opening is the separation of the contact, under
load, at a low rate and limiting the contact separation to a very
small fraction of that required for DC control.
On AC, the voltage passes through zero voltage every
1/2 cycle, on 60 cycle frequency every 1/120 of a second. By
opening the contacts slowly, the arc is suppressed by the zero
voltage. By limiting the break, the contact gap is not ionized
and air insulation prevents arc formation and restriking.
This control of the opening is essential on inductive and motor
loads when, due to low power factor, voltage surges occur on
opening the circuit.
Bryant AC switches are designed so the contacts are closed
with controlled contact closing pressure by utilizing the
flexibility of the resilient contact carrying arm.
The contacts, of a special non-oxidizing silver alloy, are opened
by a simple cam operation which limits the speed and opening.
The indexing of the handle is by an elastomer rocker or simple
cantilever steel rod. This provides a minimum of parts, along
with a solid and dependable design.
AC Test Requirements
When AC general use switches were considered by the
industry and Underwriters Laboratories, Inc., thought was
given to the ratings and it was decided to rate the switches in
accordance with NEC® branch circuit ratings of 15, 20 and 30
amperes. It was also decided to test the switch for all the loads
that could be applied to a branch circuit. Therefore, all AC
switches are tested on resistance, tungsten lamp and inductive
loads to 100% of switch rating.
Underwriters Laboratories Test Requirements for
AC General Use Switches
In order to be listed by Underwriters Laboratories, Inc., all 15,
20 and 30 ampere AC 120/277 volt switches must perform,
without failure, the following sequence of tests.
1. An overload test of 100 cycles at 4.8 times rated current
and 40-50% power factor and rated voltage. This overload
test is performed at 144 amps, 277 volts for 30 ampere
switches, at 6 cycles per minute.
2. 10,000 cycles on a plain resistance load at full rating of 15,
20 or 30 amperes, at 277 volts at 24 cycles per minute.
3. 10,000 cycles on an inductive load of either 15, 20 or 30
amperes at 277 volts, 80% power factor at 24 cycles
per minute.
4. 10,000 cycles at 15, 20 or 30 amperes, 120 volts on a
tungsten filament lamp load, at 6 cycles per minute.
5. Heat rise at test-rated load. In this test, temperature rise
must not exceed 30 degrees C.
6. A switch shall withstand, without breakdown, 1500V for
1 minute between live parts of opposite polarity and
between live parts and dead metal parts, with the switch
at the maximum operating temperature reached in
intended use.
Explanation of “Horsepower” Ratings
Performance of Bryant Switches Exceed Underwriters
Laboratories’ Requirements.
Switches marked with Horsepower Ratings are suitable for
controlling the Motor Loads of the HP ratings shown on the
switch as well as for lower HP ratings.
To qualify for an HP rating, a switch is tested at six (6) times
the full load Motor Current corresponding to the HP rating
marked on the switch. (For DC Motor Controllers, the test is
made at 10 times the full load Motor Current corresponding to
the DC HP rating marked on the switch). The test consists of
50 on-off operations at this load and the test is conducted on
six (6) samples. For 3/4 HP 120 volts-240 volts AC rating, two
(2) sets of six (6) samples each are tested in addition to the
regular overload endurance, heating and insulation tests. The
test circuit characteristics are:
For 3/4 HP For 3/4 HP
120 Volts AC 240 Volts AC
Closed Circuit Volts 120 Volts AC 240 Volts AC
Current 82.8 Amps 41.4 Amps
PoweS-Factor 0.40-0.50 0.40-0.50
Note: Current at 240V AC is 1/2 that at 120V AC.
All switches must be in good operating condition after the tests
have been completed. There must be no excessive arcing,
welding or burning of the contacts nor arc-over to ground (the
switch frames are grounded during the stalled rotor test).
AC Switch and Horsepower Ratings
NEC® is a registered trademark of the National Fire Protection Association (NFPA).