I am trying to design a basic variable trip circuitry that will trip when device pulls equal to or greater than 1/4A (primary or line current). I intend to have this circuitry as a plug-in. In other words, I will plug-in the trip circuit to 120VAC receptacle > then plug-in device into trip circuit. I have seen that there are many relay CTs. I have not seen any for such low currents and nothing "variable". Any thoughts/ideas ?

 

Once it has tripped the current will no longer be excessive. Should the device then latch in the off state? How will it be reset?
Perhaps something as simple as a reed relay could be used as the basis for the circuit, with an adjacent permanent magnet (or secondary electromagnet) which can be positioned to aid or oppose the relay coil's field to adjust the trip point. Or the relay's coil could slide along the relay body to adjust the trip point.
Another option might be to hack a GCFI/ELCB.

 

What's the purpose of such a low value trip current?

 

I am trying to design a basic variable trip circuitry that will trip when device pulls equal to or greater than 1/4A (primary or line current). I intend to have this circuitry as a plug-in. In other words, I will plug-in the trip circuit to 120VAC receptacle > then plug-in device into trip circuit. I have seen that there are many relay CTs. I have not seen any for such low currents and nothing "variable". Any thoughts/ideas ?

We need more spec's;
Duration time before trip should occur. ( to avoid a rush in current trip)
How many outputs at what voltage?
should each output carry the same circuitry?
Warning needed led/sound both?
Reset manual?
Reset automatic if so define conditions.
Housing and safety.

Picbuster