First Shelly 1PM Mini Gen 4 Installed Behind Switch
Photo Details
- Date: April 22, 2026
- Time: 7:40 PM EDT
- Weather: Clear, 58°F, 8 mph winds from the east; calm spring evening.
- Phase: Interior electrical — owner DIY (first smart-relay install)
- Location: 309 E. 7th St., Clare, MI — garage interior, switch box
- View: Close-up of the open switch box before device goes into the wall
Description
First owner-installed smart relay in the garage. A Shelly 1PM Mini Gen 4 (red module, lower right) is wired in behind the interior switch at the entry door that controls the exterior soffit lights — currently the only live switch in the garage, installed by SLS Electric on 2026-04-08. The switch is mounted indoors next to the walk-through door; the “exterior” in the circuit name refers to the fixtures it drives (the three soffit wafer lights), not the switch location. The box is a blue Carlon 2-gang new-work box; the left gang holds the soffit switch (and the Shelly behind it), and the right gang is intentionally left empty for a future interior light switch the owner will wire during the interior electrical phase. Splices are made with Wago 221-series lever nuts — an orange 5-port on the hot/load side and a clear 3-port for the neutrals. Commissioned onto the new garage Wi-Fi (Ubiquiti U6+ AP) the same day, so this is also the first device validating end-to-end network coverage in the building.
The 1PM Mini Gen 4 is the newest, smallest form factor in the Shelly lineup — short enough to tuck behind a toggle in a standard-depth box, with per-circuit power monitoring built in. The topology plan (Switch Topology & Smart Relay Placement) originally called for a Shelly Plus 1 at this location; switching to the 1PM Mini adds power monitoring at essentially the same cost and fits a shallower box. Going forward, the Mini Gen 4 is the default for every garage lighting switch where load allows — at 8A max, it clears every planned lighting zone with significant headroom.
Visible Elements
- Shelly 1PM Mini Gen 4 (red): 110–240V AC, 8A max (per Shelly spec); terminal labels visible (L / N / O / SW / I)
- Single-pole toggle switch: White residential toggle (the interior entry-door switch controlling the exterior soffit lights) set aside from the box for wiring
- Wago 221 lever nuts: Orange 5-port (hot splice), clear 3-port (neutral splice)
- Carlon blue 2-gang plastic box: Left gang populated with the soffit switch; right gang empty for future interior switch
- NM-B cable entering the top of the box; cable print partially visible
- Bare-copper ground splice at the back of the box — the grounds are joined by a twist only, with no wire nut or green crimp sleeve visible
- Framing: Painted door trim/jamb adjacent to the box; OSB sheathing and framing stud behind
Observation: Ground Splice Method (SLS Original Work)
When the switch was pulled to install the Shelly, the equipment grounds from the incoming cables were found joined by a twist only — no wire nut, no green-topped “Twister” connector, no crimp sleeve.
Code requirement
Michigan adopts the NEC as the Michigan Electrical Code (Part 8 Rules under Act 230 of 1972) without amending §250.8. NEC 250.8(A) restricts equipment-ground splicing to a short list of methods:
- Listed pressure connectors
- Terminal bars
- Pressure connectors listed as grounding/bonding equipment
- Exothermic welding
- Machine screws engaging ≥2 threads (or secured with a nut)
- Thread-forming machine screws engaging ≥2 threads in the enclosure
- Connections that are part of a listed assembly
- Other listed means
A bare hand-twist is not on that list — so it’s non-compliant regardless of how tight it is.
Compliant fixes (cheapest to fussiest)
| Fix | Notes | Approx. cost |
|---|---|---|
| Green-topped grounding wire nut (Ideal “Twister Greenie” 30-092, B-Cap Grounding, etc.) | Has a hole in the top so one ground passes straight through as a pigtail — no cut required. Purpose-built for this job. | ~$0.30 ea |
| Wago 221 lever nut (5-port, same as already in-box for hot) | UL 486C-listed for grounding conductors; a 5-port 221 takes all the grounds plus a pigtail out to the Shelly. Simplest answer here because Wagos are already on-hand. | ~$0.70 ea |
| Standard listed wire nut (red/yellow/tan sized for the AWG count) with a pigtail | Works but requires cutting a pigtail lead. | ~$0.10 ea |
| Crimp ground sleeve (Ideal Crimp-on Greenie) | Permanent; needs a dedicated crimper. Overkill for a residential switch box. | ~25 crimper |
All four satisfy NEC 250.8(A)(1) as “listed pressure connectors” and all four are acceptable to Michigan inspectors.
Plan
Dropping a Wago 221 5-port on the grounds with a pigtail to the Shelly is the easiest path — the Wago is already proven in this box, and nothing needs to be recut. When the second gang gets its interior switch, bring that cable’s ground into the same (or a second) Wago. The same spot-check should happen at every other SLS-terminated box as it’s opened during the interior DIY phase.
Next Visit: Adding the Interior Light Switch + Shelly #2
The second gang in this box will get a toggle for the interior lights and a second Shelly 1PM Mini Gen 4 behind it. Because the interior lights are a separate branch circuit from the soffit (different breaker), the hots and neutrals must stay segregated from the existing splices — NEC 200.4(B) / 300.3(B) prohibit sharing a neutral across circuits that don’t share a handle-tied breaker. Grounds, however, are supposed to be bonded together everywhere, so all grounds from both circuits land in a single Wago — which is also the moment to replace the bare twist with a listed connector.
Final splice map
| Splice | Wago | Wires in |
|---|---|---|
| Soffit hot | Orange 5-port (existing) | Incoming soffit L + Shelly #1 L + soffit toggle |
| Soffit neutral | Clear 3-port (existing) | Incoming soffit N + outgoing soffit N + Shelly #1 N |
| Interior hot | New 3-port | Incoming interior L + Shelly #2 L + interior toggle |
| Interior neutral | New 3-port | Incoming interior N + outgoing interior N + Shelly #2 N |
| All grounds | New 5-port (replaces bare twist) | 2× existing grounds + new circuit ground + Shelly #1 G + Shelly #2 G |
Parts to stage before the visit
- 2× Wago 221-413 (3-port, for interior hot and interior neutral)
- 1× Wago 221-415 (5-port, for the combined ground splice)
- 1× Shelly 1PM Mini Gen 4 (same as the first install)
- 1× Leviton-style single-pole toggle, white (or whichever finish you settle on for the whole garage)
- Short green pigtail wire (12 or 14 AWG bare/green) — for the Shelly grounds if you don’t have spare cable ends
Box-fill check before the drywall goes up
The existing 2-gang new-work Carlon is fine for the current single-device install, but after the second Shelly goes in the total fill is: two devices + five Wagos + all conductors from both cables. Verify against NEC 314.16 before committing:
- Count each conductor entering the box (hot + neutral + ground per cable = 3 × number of cables)
- Add 2 for each device yoke (switch + Shelly counts as the device it sits behind)
- Add 1 for all grounds combined (regardless of count)
- Multiply by the AWG’s cu-in requirement (12 AWG = 2.25 cu-in each; 14 AWG = 2.0 cu-in each)
If the math exceeds the printed capacity on the box (typical 2-gang shallow new-work is 22-25 cu-in), swap for a deep 2-gang new-work (Carlon makes ~35 cu-in variants) or a mud ring on a 4-square metal box before drywall. Much easier to upsize the box now than to cut drywall later.
Open-box spot-check for other SLS-terminated boxes
When each of the other SLS-wired boxes is opened during the interior DIY phase (panel knockouts, GFCI outlets, generator inlet cover, etc.), peek at the ground splice method. If any others are bare-twist, apply the same Wago fix.
Related Notes
- Switch Topology & Smart Relay Placement — design rationale for Shelly placement
- Network Planning — garage AP and low-voltage infrastructure
- Project Timeline