Electronic digital overload relays containing a microprocessor may also be used, especially for high-value motors.
3.
A second type of thermal overload relay uses a eutectic alloy, like a solder, to retain a spring-loaded contact.
4.
Larger motors have a protective overload relay or temperature sensing relay included in the controller and fuses or circuit breakers for over current protection.
5.
Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided.
6.
Motor control contactors can be fitted with short-circuit protection ( fuses or circuit breakers ), disconnecting means, overload relays and an enclosure to make a combination starter.
7.
Other protective equipment includes the voltage relay ( which trips if the voltage in the high-voltage circuit falls below 2400 V ), the dynamotor / compressor overload relay, the heating circuit overload relay, and the automatic control shutoff switch.
8.
Other protective equipment includes the voltage relay ( which trips if the voltage in the high-voltage circuit falls below 2400 V ), the dynamotor / compressor overload relay, the heating circuit overload relay, and the automatic control shutoff switch.
9.
Such overloads should sound an alarm at the control center, and the operator should take action, such as closing a bus tie or correcting an abnormal switching configuration due to an oops error ( OOPS, WE PUT THE TOWN ON A 1 LINE FEED WHEN IT TAKES 3 LINES TO SUPPLY IT . ) Some utilities have " transformer overload relays " which do trip a transformer when it is so overloaded as to exceed its short term emeregency rating, because transformers can take months to replace, much longer than burned down conductors.
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