I have a fairly standard setup here. A lamp controlled by 3 switches, the middle of which is a 4-way switch (but I think that's fairly irrelevant). I would like to add an extra lamp, controlled by the same 3 switches. It would be no problem if it were near the first lamp, but it is actually right next to the switch named S2 below. I can't run another wire back from S3 to S2. How can I wire things?
I was thinking of adding an SPST relay near S2 as shown below. Would that work? Is there a better solution?
Best Answer
Be aware that any voltage drop across the relay coil will make LS1 correspondingly dimmer, so choose the correct type of relay. For this series-wired application you want a current-actuated relay rather than a voltage-actuated type.
A simple current-actuated relay has only a few turns in its coil, which is wound with wire sized to handle a lot of current. For your application the winding might have one to three turns, and the wire must be at least as large as your household wiring.
When you shop for the relay, you may find it easier to buy an electronic device than a simple relay. This would probably operate on the same principles as a GFCI. Its voltage drop and power consumption will be too small to measure. Such a device may require its own constant-hot and neutral connections, which fortunately you have available at S2.
One disadvantage with this circuit is that if lamp LS1 burns out or is unscrewed, lamp LS2 cannot be switched on. - Nevertheless I believe you have devised the best solution for the constraints as described.