switch..

Do you mean "something is turned on connected to the output"?

That's a bit complex, could you live with when a switch on outlet C is turned on? The switch would simply when in the "on" position select output C, the off position would activate B.

Ok, if there is a positive current flowing through C then the circuit between A & B will be cut.. If there is no current flowing through C then then circuit between A & B becomes active. What kind of switch would do that ?

What you ask for is similar to a device for protecting washing machine water supplies, where one circuit controls another. A 2nd circuit is turned off to close the water supply valve when the washer is off.

Of course, your request is for the opposite result (2nd circuit off when the 1st is used), so you may have to modify the device, or perhaps the manufacturer makes it with different options.

Kevin

Right, that's unfortunately a bit complex. You'd looking at either a current relay, or a complex bit of electronics. What sort of load do you want it to activate on? If it's something like a heater, then it's going to be much easier than if it must trigger on a clock.