Electrical connection that is "AND NOT" gate

I need to create an electrical switch on normal net voltage (230V) that sort of acts like an "AND NOT" gate.

All I have at the moment is three copper wires and some connectors. Obviously, when I just connect them, I'll get power on C when A or B are powered. What I need is power on C when A is powered and B is not.

How can I connect my wires to get this, or what do I need to buy in order to end up with what I need?

• Are the voltages on A and B in phase with each other? Oct 6, 2015 at 11:54
• Yes I guess so. A and B are controlled by thermostats that cut or pass through net power. Oct 6, 2015 at 12:01
• Don't bet on them being in phase.
– JRE
Oct 6, 2015 at 12:09
• You can't implement 'not' with wires and switches. Oct 6, 2015 at 12:22

A changeover relay should do the trick, although I have made the following assumptions:

1. C is allowed to draw power from A.
2. You have a Neutral/non-earth return path for the coil and B.

simulate this circuit – Schematic created using CircuitLab

• No power from A? No power to C.
• Power from B? No power to C.
• You've just made a nice 60 Hz buzzer which will destroy the relay in a matter of hours. Oct 6, 2015 at 12:42
• @DmitryGrigoryev How so? A relay with a coil suitable for AC operation is implied in the answer, as are appropriate contact specifications. Oct 6, 2015 at 12:55
• Ok, got it. Sorry for the trouble. Oct 6, 2015 at 13:00

You could do this with a single change over (C/O) relay, with its coil powered from B - use the normally closed (NC) contacts to connect C to A