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A
contactor is a very heavy-duty relay used for
switching electric motors and lighting loads. With
high current, the contacts are made with pure
silver. The unavoidable arcing causes the contacts
to oxidize and silver oxide is still a good
conductor. Such devices are often used for motor
starters. A motor starter is a contactor with
overload protection devices attached. The overload
sensing devices are a form of heat operated relay
where a coil heats a bi-metal strip, or where a
solder pot melts, releasing a spring to operate
auxiliary contacts. These auxiliary contacts are in
series with the coil. If the overload senses excess
current in the load, the coil is de-energized.
Contactor relays can be extremely loud to operate,
making them unfit for use where noise is a chief
concern. |
