Uncle Ed’s 3-Way Diagram — Garage Floor Lights
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Photo Details
- Date: June 19, 2026
- Time: 6:58 PM EDT
- Weather: Clear June evening, ~upper 60s°F cooling toward the 60°F overnight low. Evening work session in the still-unconditioned garage; temps comfortable.
- Phase: 120V electrical rough-in (in progress) — garage floor (bay) lighting 3-way
- Location: 309 E. 7th St., Clare, MI (diagram on the shop workbench)
- View: Hand-drawn reference diagram (not an install photo)
What This Is
A hand-drawn 3-way switch reference diagram from Uncle Ed, used as the starting point for wiring the garage floor (bay) light 3-way circuit. The drawing shows the textbook 3-way: a 120 VAC power panel, two switches, and a light, with conductors labeled B (black), R (red), W (white), G (ground).
The diagram depicts the standard topology — power into one switch, 3-conductor between the two switches, and the light fed from the far end. Our actual install deviates from this in one deliberate way, documented below.
Our Implementation — How It Differs From the Standard
The usual run is Panel → switch → switch → light (power enters at one switch, daisy-chains through travelers to the second switch, then out to the light).
Ours is Panel → stairwell switch → (splits) → entry-door switch + up to the light:
- Power comes in from the panel at the stairwell switch box, not the entry-door switch.
- 12/3 runs from the stairwell box to the main entry/service-door switch.
- The light (garage floor lights) is also fed from the stairwell box (“up to the light”).
Because the line and the load are both at the stairwell end, the far (entry-door) switch’s common output has to travel back to the stairwell box to reach the light. There aren’t enough conductors in 12/3 to do that and carry a neutral, so:
- Black + Red = travelers (connected normally between the two switches).
- White = the switched-hot return — it carries the hot out of the entry-door switch’s common back to the stairwell box, where it joins the cable going up to the light.
- Because that white is now an ungrounded (hot) conductor, not a neutral, it was re-identified with black tape stripes on both ends and labeled with the P-touch. This is required and correct per NEC 200.7(C)(2) (a white-in-cable conductor used as ungrounded must be permanently re-identified with a color other than white/gray/green at every accessible point). The P-touch labels are extra insurance for a less-common configuration — exactly the kind of thing that prevents a head-scratch during future troubleshooting.
This arrangement also makes the stairwell box a power-distribution hub: since the constant panel hot + neutral land there, the box also feeds the separate stair-lights 3-way circuit.
Conductor map — 12/3 between stairwell box and entry-door switch
| Conductor | Normal role | Role in this circuit | Marking |
|---|---|---|---|
| Black | Hot / traveler | Traveler | none |
| Red | Traveler | Traveler | none |
| White | Neutral | Switched hot — return from the entry-door switch common → back to stairwell box → up to the light | Black tape stripes both ends + P-touch label |
| Bare | Ground | Ground | bare |
Switch-common assignments
- Stairwell 3-way common → panel line hot (incoming power).
- Entry-door 3-way common → switched output, returned on the re-identified white back to the stairwell box and up to the light.
- Light: switched hot = the re-identified white (via the up-to-light cable’s black); neutral comes from the panel neutral spliced through the stairwell box.
Stair Lights — The Conventional 3-Way (for contrast)
The stair lights (stairwell ↔ upstairs landing) deliberately use the standard topology: Panel → stair switch → upstairs switch → light, wired with the new 14/3 (light blue Cerrowire, HD Order WK29485627). Because that run is 14 AWG, the stair-lights circuit must be on a 15 A breaker (NEC 240.4(D)) — see breaker sizing rationale.
Shelly Relay Placement (and the entry-door neutral)
The Shelly relays are placed at the boxes that have constant L + N, which sidesteps the missing-neutral issue created by the white-as-hot 12/3:
| Circuit | Shelly location | Why it works |
|---|---|---|
| Garage floor (bay) lights | Lower stairwell / garage light box | This is the power-distribution hub — the panel home run lands here, so it has constant hot + neutral for the Shelly. The entry-door switch is just a wired input to the Shelly (no neutral needed there). |
| Stairwell lights | Upstairs stair switch | Shelly lives at the upstairs switch box for this circuit. |
So the entry-door switch box not having a neutral is a non-issue — no powered device lives there; it’s purely a 3-way input to the Shelly in the stairwell/garage box.
Two things to confirm at install
- Upstairs box needs constant L + N for its Shelly to function — make sure that box gets a constant hot and neutral (not just switched travelers), consistent with placing the relay there.
- NEC 404.2(C) (neutral required at switch locations) is a per-box code item independent of the smart-relay plan. The stairwell/garage box and the light boxes have neutrals; the entry-door box does not (its 12/3 white is a hot). Worth a quick check against the inspection scope for this circuit, even though no device will live in that box.
No shock/fire hazard in the as-built — the white re-identification is correct and the circuit functions. These are code / function-at-install items, not safety defects.
Related Notes
- Electrical Planning — Switch Topology & Smart Relay Placement
- Electrical Materials Order — 12/3, 14/3, and devices for these circuits
- West wall rough-in (same day)
- Uncle Ed wiring the stairwell switch box (2026-06-07) — the same box that serves as the power-distribution hub here
- Project Timeline