Contactor

Sometimes an economizer circuit is also installed to reduce the power required to keep a contactor closed; an auxiliary contact reduces coil current after the contactor closes. A somewhat greater amount of power is required to initially close a contactor than is required to keep it closed. Such a circuit can save a substantial amount of power and allow the energized coil to stay cooler. Economizer circuits are nearly always applied on direct-current contactor coils and on large alternating current contactor coils.

Sometimes an economizer circuit is also installed to reduce the power required to keep a contactor closed; an auxiliary contact reduces coil current after the contactor closes. A somewhat greater amount of power is required to initially close a contactor than is required to keep it closed. Such a circuit can save a substantial amount of power and allow the energized coil to stay cooler. Economizer circuits are nearly always applied on direct-current contactor coils and on large alternating current contactor coils.

A basic contactor will have a coil input (which may be driven by either an AC or DC supply depending on the contactor design). Universal coils (driven by AC as well as DC) are also available in the market today.<ref>Electrical Classroom,[https://www.electricalclassroom.com/contactor-construction-operation-application-and-selection], Contactor – Construction, Operation, Application and Selection</ref> The coil may be energized at the same voltage as a motor the contactor is controlling, or may be separately controlled with a lower coil voltage better suited to control by [[Programmable logic controller|programmable controllers]] and lower-voltage pilot devices. Certain contactors have series coils connected in the motor circuit; these are used, for example, for automatic acceleration control, where the next stage of resistance is not cut out until the motor current has dropped.<ref>{{Harvnb|Croft|Summers|1987|loc=p.&nbsp;7-125<!--hyphenated page-->}}</ref>

A basic contactor will have a coil input (which may be driven by either an AC or DC supply depending on the contactor design). Universal coils (driven by AC as well as DC) are also available in the market today.<ref>Electrical Classroom,[https://www.electricalclassroom.com/contactor-construction-operation-application-and-selection], Contactor – Construction, Operation, Application and Selection</ref> The coil may be energized at the same voltage as a motor the contactor is controlling, or may be separately controlled with a lower coil voltage better suited to control by [[Programmable logic controller|programmable controllers]] and lower-voltage pilot devices. Certain contactors have series coils connected in the motor circuit; these are used, for example, for automatic acceleration control, where the next stage of resistance is not cut out until the motor current has dropped.<ref>[[Terrell Croft]] and Wilford Summers, ''American Electricians' Handbook, Eleventh Edition'', New York: McGraw Hill (1987) {{ISBN|0-07-013932-6}} p.&nbsp;7-125<!--hyphenated page--></ref>

==Operating principle==

==Operating principle==