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Time-delay relay contacts must be specified not only as either normally open or normally closed, but whether the delay operates in the direction of closing or in the direction of opening. The following is a description of the four basic types of time-delay relay contacts. First, we have the normally open, timed-closed (NOTC) contact.
Dry contact may mean any of the following in electronics: . No current: A dry contact is the synonym of volt free — it is not "wetted" by a voltage source.Dry contact can refer to a secondary set of contacts of a relay circuit which does not make or break the primary current being controlled by the relay.
When relay contacts open to interrupt a high current with an inductive load, a voltage spike will result, striking an arc across the contacts. If the voltage is high enough, an arc may be struck even without an inductive load.
Today, microprocessor-based relays can perform many protective functions in one device. [1] When one device performs several protective functions, it is typically denoted "11" by the standard as a "Multifunction Device", but ANSI Device Numbers are still used in documentation like single-line diagrams or schematics to indicate which specific ...
Typical contact elements of an electromechanical relay or contactor. A “contact” is a pair of electrodes (typically, one moving; one stationary) designed to control electricity. Electromechanical switches, relays, and contactors “turn power on” when the moving electrode makes contact with the stationary electrode to carry current.
An instantaneous over-current relay is an overcurrent relay which has no intentional time delay for operation. The contacts of the relay are closed instantly when the current inside the relay rises beyond the operational value. The time interval between the instant pick-up value and the closing contacts of the relay is very low.
NEMA contact ratings are how much current at a rated voltage a relay or other pilot device can switch. The current rating of smaller NEMA contactors or their auxiliaries are defined by NEMA ICS 5: Industrial Control and Systems, Control Circuit and Pilot Devices [1] standard. The nomenclature is a letter followed by a three-digit number, the ...
The contacts are the current-carrying part of the contactor. This includes power contacts, auxiliary contacts, and contact springs. Contact material is chosen for high electrical conductivity, mechanical strength, and stability under arcing and oxidation. Commonly used metals include alloys of tungsten, molybdenum, copper, and others.
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