Contactors and Relays

Contactors and Relays are other names for industrial switches.  Both contactors and relays rely on coils to cause contacts to close thus changing the switch from a closed to open position or from a open to a closed position. If the contactor or relay is usually open when de-energized, it is called Normally Open, and vice versa, if it is closed in the de-energized state then it is Normally closed.  A normally open (NO) contactor or relay is more common than normally closed (NC).  The main reason is that the relay or contactor will "fail" in the open position when power is lost to the coil.

Contactors and relays are used to close a circuit to "turn on" and allow electrical flow into a system or a device.  A coil is used to open and close the contacts.  The coil voltage can be a different voltage than that is switched.  The most common coil voltages are 120/60, 24/60 and 24vdc.  The most common switched voltages are 120/60, 240/60 and 480/60.  

Contactors and relays are sized in amperes or amps. Also, they come in single pole, double pole, three pole and four pole.  The most common are single pole and three pole; three pole for three phase power systems.  The two common types of loads are resistive and inductive.  A resistive load is normally a heating load.  A resistive load does not normally have an inrush current. Howeve, some high temperature heating elements for ovens do have high inrush. Inductive loads such as motors and lighting do have inrush currents and these inrush currents need to be addressed when sizing an appropriate contactor.  To figure amps please use our OHM's law calculator.

Types of Contactors and relays are:

Mercury Contactors

Mechanical Contactors

Solid State Relays

Cube relays

SCR controls

Mercury Contactors or Mercury Displacement Relays

Mercury contactors are a great way to switch industrial loads on and off.  Mercury contactors or MDR's (Mercury Displacement Relays) can be the best option for electric heating elements.  The Mercury relays have very long life, millions of cycles, are quiet and can be cycled up to once every second.  Mercury Relays far outlast and out perform mechanical contactors and relays which can have only 100,000 cycles and be limited to switching once every 30 to 60 seconds.  Normally closed mercury relays are also used for traffic control to control blinking lights as they have the long life and higher temperature resistance  than other types of contactors, especially solid state relays.

Mercury Displacement Relays are all designed and built to meet the most exacting demands of industry. They have won their high place in the electrical field by doing the tough and tricky jobs that ordinary equipment could at best do in an uncertain manner. They have proved their ability to stand up under the most adverse conditions of temperature, dust and moisture, in all types of applications. All the care required for the manufacture of high-grade instruments is used in the manufacture of the switches. All switch parts are specially cleaned, and contamination is avoided by use of tweezers, gloves, etc., when making assemblies.

Contactors are hermetically sealed with high quality glass to metal seals.
The stainless steel tube is totally encapsulated in high grade UL approved epoxy to prevent moisture damage and voltage breakdown through the protective coating.
The coils are wound on compact nylon bobbins and molded onto the metal tube to provide minimum power loss. This allows for low coil power required to actuate the contactor. This also enables the units to handle high loads with minimum derating due to higher ambient temperatures.
Inert gases internally prevent excessive arcing between the mercury and the electrodes which enables the unit to function for millions of cycles with very low contact resistance, and minimum deterioration of the internal parts.
Available in all standard coil voltages, in single, two and three pole arrangements. Other coil voltages available upon request.
In multiple pole units each tube is actuated by its own coil. This eliminates pull-in variation between contact tubes, assuring consistent switching.

FEATURES

ADVANTAGES OVER ELECTROMECHANICAL AND SOLID STATE RELAYS Superior Performance and Reliability Long life Durable Compact Size Low, Predictable Contact Resistance Reduced RFI for Improved Interface Capability Handles a Variety of Loads Increases design flexibility Rapid On-Off Cycling Capability Mercury quickly dissipates contact heat Low Coil Power Requirements Minimal Derating Due to Higher Ambient Temperatures Quiet Action DESIGN & CONSTRUCTION Contacts are within a hermetically sealed steel body Impervious to adverse conditions No external arcing Arcing is in a gaseous atmosphere Quenches the arc Extends relay life Only one moving part (the plunger) No buttons to pit, weld or burn out One coil for each set of contacts Assures consistent switching Minimizes pull-in variation between contacts Epoxy encapsulated Moisture resistant High dielectric strength Permanently fixes contacts to coil; eliminating possible misalignment Helps dissipate heat and noise Rugged (impact resistant) BENEFITS Reduction of Operational and Maintenance costs Increases Utilization and Productivity of Equipment By reducing down-time Installation and service is a routine operation Simple to install No sophisticated equipment is required Easy to trouble-shoot TYPICAL APPLICATIONS FOR MDI's MERCURY DISPLACEMENT CONTACTORS LIGHTING Auditorium Lighting Copy Equipment Dimmer Controls Display Signs Emergency Lighting Flood Lights High Intensity Lamps Hospital Lighting Lighting Test Panels Mercury Vapor Lamps Parking Lots Photography Lighting Scoreboards Sodium Vapor Lamps Stage Lighting Street Lighting Tower Control Traffic Signal Tungsten Lamps GENERAL APPLICATIONS Air Conditioning Alarm Systems Automatic Door Closers Battery Chargers Blue Print Machines Copiers Computer Power Supplies Corrosive Locations Dusty, Oily Locations Dry Cleaning Equipment Energy Management Systems Farm Incubators & Brooders High Cycle Rate Applications Low Voltage Switching Marking & Engraving Equipment Motor Starting Soldering Systems Telephone Switching Test Panels Vapor Degreasers X-Ray Machine Controls ELECTRIC HEATERS Baseboard Heaters Blow Molding Cabinet Heaters Chemical Tank Heaters Curing Furnaces Drying Ovens Duct Heaters Film Packaging Glass Furnaces Heat Lamps Heat Sealing Machines Induction Heater Industrial Ovens Infrared Heaters Ink Drying Ink Heating Injection Molding Machines Kilns Lab Ovens Packaging Equipment Plastic Extruders Quartz Heaters Radiant Heaters Roof Top Heating Shrink Tunnels Unit Heaters Vacuum Forming FOOD INDUSTRY EQUIPMENT (HEATERS) Baking Ovens Coffee Urns Deep Fryers Dishwashers Electric Grills Electric Ranges Pizza Ovens Steam Generators SPECIALTY APPLICATIONS Capacitor Discharge Systems Hazardous Locations Phase Converters Tower Control