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majesus (Electrical) (OP)
6 Oct 08 18:01
In Circuit Breaker applications, what is the difference between a Shunt Trip and a Trip Coil?

For instance in one 600V PDC drawing, I see that the relay which trips the 2000A secondary CB is labeled as "ST."

However, for the 4kV PDC drawing, I see that the relay coil that trips the 2000A secondary CB is labeled as "TC."

The intended purpose of both types is to trip the CB (that's easy! j/k)... But I'm curious, what is the difference between the two types?  

alehman (Electrical)
6 Oct 08 20:56
To my knowledge they are one and the same. Usually "shunt trip" is a term used in low voltage, e.g. molded case, circuit breakers where it is commonly and add-on component. For power breakers, it is a standard component and is more commonly called a "trip coil".
bfuchs (Electrical)
6 Oct 08 21:07
A "trip coil" can be either :
- shunt trip coils : were the application of voltage causes the coil to trip the breaker
- an undervoltage trip coil : where removing the voltage causes the coil to trip the circuit breaker (or application of voltage of voltage is required to close and maintain the breaker closed)
waross (Electrical)
6 Oct 08 21:44
A shunt trip is a voltage coil. Some trip coils may be current dependent.

"Why not the best?"
Jimmy Carter

majesus (Electrical) (OP)
8 Oct 08 2:43
Thank you guys... You know, I called the engineer who drew these drawings and asked him, because I am ALWAYS curious about these things and it will bug me until I learn why...

Like Aleham said, "shunt trip" is the term used in low voltage, e.g. molded case, circuit breakers where it is commonly an add-on component. The CB has thermal/magnetic trip capabilities, but it also has the ability to trip electronically say from a Feeder Protection Relay say like the GE SR750.

"Trip Coil" was used in reference to Power CB (in this case Medium CB.) The CB has no thermal/magnetic trip capabilities, it requires "brains" to tell it when to trip electronically from a monitoring relay such as the GE SR750 :)



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