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2. Mercury relay - Wikipedia

   en.wikipedia.org/wiki/Mercury_relay

   Normally closed mercury relay, with coil around top of tube and adjustable angle. A mercury relay (mercury displacement relay, mercury contactor) is a relay that uses mercury as the switching element. They are used as high-current switches or contactors, where contact erosion from constant cycling would be a problem for conventional relay contacts.

3. Contactor - Wikipedia

   en.wikipedia.org/wiki/Contactor

   A contactor is an electrically controlled switch used for switching an electrical power circuit. [1] A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch. Unlike general-purpose relays, contactors are designed to be ...

4. Relay - Wikipedia

   en.wikipedia.org/wiki/Relay

   SPST-NC (Single-Pole Single-Throw, Normally-Closed) relays have a single Form B or break contact. As with an SPST-NO relay, such a relay has four terminals in total. SPDT (Single-Pole Double-Throw) relays have a single set of Form C, break before make or transfer contacts. That is, a common terminal connects to either of two others, never ...

5. NEMA contact ratings - Wikipedia

   en.wikipedia.org/wiki/NEMA_contact_ratings

   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 ...

6. Magnetic starter - Wikipedia

   en.wikipedia.org/wiki/Magnetic_starter

   Contactor with overload relay. A magnetic starter is an electromagnetically operated switch which provides a safe method for starting an electric motor with a large load. Magnetic starters also provide under-voltage and overload protection and an automatic cutoff in the event of a power failure.

7. Reed switch - Wikipedia

   en.wikipedia.org/wiki/Reed_switch

   Reed switch. (from top) Single-pole reed switch, four-pole reed switch and single-pole reed relay. Scale in centimeters. Reed switch, contact detail. Commonly-used circuit symbol. Operation of the reed switch. The reed switch[i] is an electromechanical switch operated by an applied magnetic field. It was invented in 1922 by professor Valentin ...