When i change the plug setting of overcurrent relay,do i have to isolate the trip ckt,or the Cts get?
Answer:
No need to isolate the trip circuit. Generally when you plug out the link to change the plug setting the setting of relay goes to maximum. Putting plug back to other setting is a matter of few seconds.
insufficient data, is it a circuit breaker, overload protection of motors or protective relays?
nope u gota short the CT secondary then do whatever u want.
Since you mention a 'plug setting', this indicates that you are either dealing with a low voltage power circuit breaker, a low voltage molded case circuit breaker with interchangeable trip units (plugs), or an 80's to early-90's vintage solid state relay.
Modern microprocessor relays allow you to change the settings on the fly. At most, the relay reboots and proceeds with the new settings.
Old electromechanical relays had taps that should not be changed unless the CTs are shorted.
However, the bigger question is: Why are you changing the setting plug!?
Has anyone checked the coordination with this revised setting? Some devices (especially low voltage power circuit breakers) require the breaker to be open and thus de-energized when the new setting plug is installed.
Other devices, especially relays, should have their calibration checked to be sure that the device is functioning properly with the revised settings.
If you can't open the power circuit to install and check the new settings, someone with a lot more expertise and authority needs to make the decision about whether to proceed on a live circuit.
Remember, electricity doesn't give 2nd chances...
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