Wiring – Quickest way to identify line wire and load wire in a multiway switch

multiway-switchswitchwiring

I am upgrading a lot of light switches in my home to Z-Wave smart switches. It is easy when it is a simple switch, but a 3-way, 4-way or n-way switch circuit is trickier. When doing so, I need to know where the hot "line" wire is and where the most downstream "load" wire is.

I am able to accomplish this but it is time consuming. My current approach is as follows:

  1. Shut power off at the breaker for the circuit
  2. Pick a switch and disconnect it
  3. Turn power back on at the breaker
  4. Probe the wires at the disconnected switch. If I find a hot wire, then go flip a switch elsewhere in the circuit and probe again. If the hot wire remains hot, I have found the most upstream "line" wire. If not, I know the most upstream "line" wire isn't at this switch. [REPEAT FROM STEP 1 with a new switch]
  5. Once the "line" wire is identified, I can then use a similar technique to identify the wire that powers the lights.

This takes a really long time, especially when other people (and children) are in the house and you have to ensure nobody else is in danger of touching an exposed wire.

I can reliably and consistently identify the line & load wires using this method, but I am really hoping someone has a hack or shortcut to quickly accomplish this same goal.

Best Answer

When you addressing two 3-ways and one 4-way. Remember that one side of the common on the three way is the line side and the other common is the load side or switch leg. The two wires that connect between the 3-ways switches are carriers. If you have a 4-way it simply flips the carriers, two carriers in two carriers out. So, no there should never be a configuration where a line side "hot" leg will be connected to the 4-way. Although it may pass through the box.

Other than that the only other way to save time is to have a helper turn the breakers on and off to save you some steps, or employ a circuit tracer to trace out the circuits. These may be well and fine for someone who is doing a large number of circuits but usually isn't cost effective for a one off DIYer.

Good luck

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