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DB High Current Switch

filnor literature DB High Current Switches

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Double-Break High Current Switches

High Current Switches for non-load switching for bus disconnecting or transfer erectifier disconnect polarity reversing. Ideal for electrolytic cell (cell shorting).

For High Current Industrial Applications

• AC/DC Switchboards
• Rectifier Disconnect Switches
• Contact Rail Switches
• Trolleyline Disconnect Switches
• Motor Control Isolation Switches
• DC Substation Switches

Bus Disconnect Switches

Bus Disconnect Switch

7000 Amperes, Manually Operated

Bus Disconnect Switch

Bus Disconnect Switch

15,000 Amperes 250 Volts DC, Pneumatically Operated

DB High Current Switch

Standard DB Switch

Pneumatically Operated

DB High Current Switch

Custom DB Switch

Pneumatically Operated


• Bolted Pressure Contact Switches
• Grounding Switches
• Hook Stick Switches
• Knife Switches
• Special Design Switches
• Transfer Switches
• Test Switches


Type DB high current switches are heavy-duty, double-break devices, which are suitable for industrial installations involving large amounts of current.

Modular basic units are available from 3000 to 9000 amperes, in multiples of 1000 amperes. They can be adapted for non-load switching for use in bus disconnecting or transfer, rectifier disconnect, polarity reversing, etc. When furnished with arcing contacts, these units can be applied for load switching when in parallel with an electrolytic cell (cell shorting), where the voltage drop across the cell is 6 Volts DC maximum.

(Consult the factory for load break ratings up to 50 Volts DC). Single units, as shown in the illustration below, from 3000 to 9000 amperes are furnished with a manual operator as standard. Larger sizes are supplied with an air cylinder operator.

Combinations of the modular basic units are available in ampere ratings of 10,000 to 36,000 amperes and larger. Other combinations are available to meet various bus arrangements, such as; two - 3000 ampere units for a 6000 ampere application, 3000 - 4000 ampere units for 12,000 amperes, four - 4000 ampere units for 16,000 amperes, 4000 - 5000 ampere units for 20,000 amperes, etc.


The manual operator consists of a cast indicating plate with stops, indicating OPEN and CLOSED, and a cast hub that has a socket for the wood handle. The hub has a pull-to-turn latch at both positions. The four methods of furnishing the manual operator are shown below.

manual operator switch

Manual Operator

NOTE: The cover, indicating plate and handle hub are at bus potential when switch is closed. The handle length varies to provide approximately 40 pounds operating effort.

Some applications of DB switches require their use in the normally open position, others in the normally closed position. When pneumatically operated, the air cylinders are continually subjected to air pressure to avoid drifting of the switch. Air cylinders are mounted as shown in the two configurations below; i.e., with the piston rods retracted into the cylinders for the position, open or closed, that is normal for the switch. This is done to minimize dirt collection and corrosion of the piston rod.

pneumatic operator switch

Pneumatic Operator

Air cylinders are sized to provide a safety factor with the recommended or specified pressure rating. Dry lubricated instrument air is recommended.

For typical DC applications the switch cover-plate, air cylinder mounting, air cylinder and linkage are at bus potential when the switch is closed. Flexible insulated air lines are required. If solenoid operated valves are used, the conduit must be insulated and flexible.

Ampere Ratings of the switches listed are based on one pair of moving contacts per 1000 amperes. The temperature rise of the switch depends on the bus temperature since they will equalize and the switch cannot run cooler than the bus. On the intermittent duty it may be possible to use a smaller rated switch depending on the open and close intervals, bus temperature and ambient conditions.

Auxiliary Switch: There are two basic uses for auxiliary switches depending upon the application. They are as follows:

General indication – Indicates approximate position of main switch contacts, within 30º of travel: e.g., when the auxiliary contacts are closed with the main contacts closed, the auxiliary contacts will open within 30º of the opening stroke of the main switch. When the auxiliary contacts are closed with the main contacts open, the auxiliary contacts will open within 30º of the closing stroke. Typical use is pilot light indication.

Specific indication – Indicates exact position of main switch contacts, open or closed, within 10º of travel: e.g., when the auxiliary contacts are closed with the main contacts closed, the auxiliary contacts will open before the main switch contacts separate on the opening stroke. When the auxiliary contacts are closed with the main contacts open, the auxiliary contacts will open as the main switch contacts just start to move toward the closed position. Besides the fully opened and closed positions, auxiliary switches can be located at various points along the arc of travel of the main movable contacts. Typical uses are interlocking or sequencing of auxiliary equipment such as pumps or fans; Not to be used to initiate the electrical control circuit of the load switching device; e.g., electrically operated circuit breaker or circuit interrupter.


auxiliarty switch arching contacts load switching arc contacts

Load Switching Arc Contacts as supplied on the 6 volt DC switches consist of one stationary and two moving arc contacts all having tungsten alloy arc tips. They provide initial contact before the main contacts on closing and break contact after the main contacts on opening. They are of rugged construction, factory adjusted and easily replaced.

Modular Construction. Basic switch modules are available in nominal ratings of 3000 to 9000 amperes, in 1000 ampere increments. Higher ampere ratings are obtained by combining two or more modules into one assembly. Modules can be factory assembled to provide single-pole, double-throw as well as multiple-pole devices. Configurations can be developed to match special bus structures.

Type DB high-current switches were developed to provide a reliable, uncomplicated and economical means of switching circuits which carry large AC or DC currents. Typical applications are as non load-break disconnects for electric furnaces, rectifiers, metal plating apparatus, and large DC motors; also as load-break shorting switches for electro-chemical industry cells and similar installations which demand high-current capacity and dependable performance under adverse conditions.

Disconnect Switches:

disconnect switch

Contacts of Type DB switches are double-break with a wiping action that is self-cleaning. The double rows of contact bars, one above and one below the terminals, are self-aligning. Each contact bar has its own stainless steel pressure spring which assures proper contact pressure under the most adverse operating conditions. Parallel construction of the movable contacts provides magnetic forces which supplement the contact pressure of the stainless steel springs.

Terminals are silver plated copper bars with slotted holes to make field
alignment of multiple switches a simple matter. The end of each terminal which connects with the main moving contacts is beveled to make the switch close easily. They are silver plated for greater contact efficiency and protection against corrosion.

Cover Plates for DC switches are constructed of sturdy steel with protective coatings to withstand the corrosive environments frequently encountered in this type of switch application. Cover plates for AC switches are made of glass polyester to avoid eddy-current losses and to provide additional insulation for the higher voltages which are common to AC installations.

Driver Mechanism is arranged so that the switch cannot be damaged due to overtravel. In the closed position there is no tendency of the contact springs to bias the contacts toward the open position because spring action of the contacts is not in the same plane as the motion of the driving mechanism. Adjustment of the mechanism is not critical. Installation with as much as plus or minus ten degrees from 'dead center' closed position can be tolerated without reduction contact area or contact pressure.

Easy Maintenance. Husky bolts clamp the terminals between the cover plates and insulators. All other principal parts are positioned and held in place by this unique construction of the switch.

If maintenance is required, Type DB switches can be easily reassembled without special jigs or tools. The telescoping insulators, together with the cover plates, automatically align the terminals without the gauging or adjustment of parts.