Electrical – Bulbs on seperate circuits triggering third bulb

circuit analysiselectrical

I would like to know if the following is possible, and if it is possible, roughly how the wiring should be done …

I have 2 light bulbs (BULB1 and BULB2) connected to SEPERATE switches. I want to install BULB3 so that BULB3 turns on when …

  1. BULB1 is on, or
  2. BULB2 is on, or
  3. BULB1 and BULB2 are both on

and turn off when …

  1. BULB1 and BULB2 are both off

I have access to the wiring at BULB1 and BULB2, and no access to the wiring at the switches. BULB3 will have to draw power from either BULB1 or BULB2.

The idea is to add a light to a dark passage where there are bulbs on both sides, but none in the middle.

Thanks for any suggestions.

Best Answer

another relay option.

schematic

simulate this circuit – Schematic created using CircuitLab

with appropriate choice of relay this layout could be used in the case where both switches are on different phases, but not all relays that can switch 240V are suided to that task.