plug/sensor

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car81

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Can someone explain the difference between the plug and the sensor on a circuit breaker? What is the function / differences of both? Thanks.
 
car81 said:
Can someone explain the difference between the plug and the sensor on a circuit breaker? What is the function / differences of both? Thanks.
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Are you asking about the difference between using the test button on a GFCI breaker and using a plug-in GFCI tester?
 
No just asking what the role of each is. When they say sensor rating, is that the CT rating? Plug rating is the max allowable continuous current allowed? Thanks.
 
car81 said:
Can someone explain the difference between the plug and the sensor on a circuit breaker? What is the function / differences of both? Thanks.
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The "sensor" of an electronic trip circuit breaker is usually what defines the maximum trip rating of the breaker. These is usually difficult to change. Short Time and Instantaneous trip functions are often, but not always, based on a multiplier of the sensor. You can think of a sensor as being similar to the internal CTs of the breaker

A "plug" modifies the sensor rating, usually by some fraction. Long Time settings are usually based on the plug settings. These are often easy to change.

Not all electronic trip devices have both sensors and plugs.

For example,
A circuit breaker might be a 1600A frame - this means it has 1600A contacts.
Its sensor rating may be 800A. If the LT setting of the trip unit only go as low as 50% then this breaker can be set as low as 400A.
It may be able to have a 25% rating plug installed which would effectively change the breaker to be 800*.25 = 200A maximum. Now by using the lowest LT setting this breaker can now be a 100A device.
 
car81 said:
(cut)When they say sensor rating, is that the CT rating? (cut)
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Yes that is a good way to look at it. The rating plug is generally an interchangeable plug-in part that tells the trip unit which sensors you installed. You can really screw up the trip unit logic putting in a different rating plug than sensors.

So why aren't the trip units just programmed for the sensor rating instead of using a plug-in part? Some trip units do that. I don't know why they all don't. If a trip unit is programmable one would think that a register for the sensor rating would not add anyting.

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