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).
