Polypool 410 Goes Smart: Shelly 1PM Mini Gen3 Plug Extension (Wi-Fi + Power Meter)

Ever wished your “regular” plug could magically become a smart plug… without a chunky external box? 😊 This project does exactly that: I took a very common Italian DIY-store plug ( Polypool 410 ) and redesigned the entire outer shell to neatly fit a Shelly 1PM Mini Gen3 inside.

Result: a compact plug extension that can:

- switch loads over Wi-Fi

- measure power/energy (W, V, A, kWh)

- keep everything tidy in a single enclosure

What’s original / what’s reused

To keep the critical parts solid and reliable, I reused from the original Polypool 410:

- the 3-pin plug insert (metal pins assembly)

- the original screws

- the blue cable clamp / strain-relief clip

And I replaced :

- the two original plastic shells → with new 3D-printed clamshells shaped around the Shelly module

BOM (what you need)

Printed parts

- 1× Front shell

- 1× Back shell

Reused parts (from Polypool 410) https://www.obi-italia.it/p/1827500/spina-salvaspazio-10-a-2p-t-uscita-cavo-a-90-nera

- 3-pin plug insert / pins assembly

- screws

- blue cable clamp (strain relief)

Electronics

- 1× Shelly 1PM Mini Gen3 https://www.amazon.it/Shelly-Mini-Wi-Fi-Interruttore-Intelligente/dp/B0CRRT6HCB

Wiring

- mains cable suitable for your country and current rating

Printing notes

- Prefer tougher / more heat-resistant materials (PETG / ASA / ABS / PC-blend).

- Use multiple perimeters and solid top/bottom for stiffness.

- Check fit: tolerances vary by printer and material.

Assembly tips

- Route wires through the internal channels before closing the shells.

- Make sure strain relief is doing its job: cable pull must not reach the terminals.

- Ensure no conductor can be pinched by the seam during closing.

- Tighten screws evenly (don’t overtighten plastic).

Known limitations / Safety notes (read before building)

- This is a DIY enclosure. It is NOT a certified electrical product.

- The Shelly 1PM Mini Gen3 is rated 8A , but for a sensible safety margin I recommend:

- Max continuous current: 6A

- At 230V → ~1380W max (6A × 230V)

- At 110V → ~660W max (6A × 110V)

- Avoid high inrush / heavy loads (examples: heaters, kettles, hair dryers, toasters, large motors, compressors).