SM323 Zigbee Dimmer: v2 vs v1 — what changed and why

The SM323 v2 has been Samotech’s current Zigbee dimmer since 2023. Compared with the v1 (2020–2023), the v2 is roughly 20% smaller, supports neutral-wire installation without a bypass capacitor, handles a higher maximum load, reports energy use directly to your Zigbee network, fits EU back boxes for the first time, removes the activation delay when lights are switched on, and works with both retractive and standard on/off light switches.

The v1 has not been manufactured since 2023. Reviews and YouTube videos published before then cover the older design and don’t reflect the current product.

This page covers everything that’s changed, what stayed the same, and which version is right for which kind of installation.

At a glance

* Mode activation available upon request at the time of purchase. Zigbee2MQTT users can change the mode on their own.

Smaller form factor (51 × 26 × 24 mm)

The v2 module shrank from 64 × 27 × 24 mm to 51 × 26 × 24 mm – about 20% less volume than the v1. In practical terms:

• It fits inside standard EU 60 mm round back boxes for the first time. Previously, EU installations needed bespoke wiring; now the v2 drops into the same boxes electricians are already using.
• In UK installations, the smaller depth leaves more room for the wiring loom – the difference between “snug” and “comfortably installed”, particularly behind metal-clad faceplates with less internal clearance.
• It fits behind a wider range of decorative faceplates without modification.

The functional output – load handling, dimming smoothness, neutral support – is unaffected by the size reduction. The v2 simply does more in less space.

Higher maximum load (350 W)

The v1 was rated for a maximum dimming load of 250 W. The v2 raises that to 350 W, a 40% increase. In practical terms, the v2 comfortably drives larger pendant fittings, multi-bulb chandeliers, and longer LED strips that would have been borderline or over-spec on the v1.

For most domestic installations – typical living-room downlights, kitchen pendants, bedroom ceiling lights – either generation has plenty of headroom. The difference matters in three situations: high-end residential lighting with multiple fittings on one circuit, commercial or hospitality installations, and any installation where you’d prefer to leave 40 – 50% headroom for future load changes.

Neutral wiring without a bypass capacitor

The v1 was a live-only dimmer. That worked in most UK installations (where neutral isn’t usually present at the switch), but with low-wattage LEDs you’d often need to fit an SM107 bypass capacitor at the load to prevent flickering or ghost-glow.

The v2 supports two wiring modes:

• Live only – same as v1, for legacy UK back boxes without neutral at the switch
• Live + Neutral – for installations where neutral is available at the switch (common in modern builds across the UK and EU)

When wired with neutral, the v2 doesn’t need a bypass for any standard LED load. Power reporting becomes more accurate, low-wattage flickering disappears, and there’s no extra capacitor to find a home for inside the back box.

The SM107 bypass capacitor remains available for legacy v1 installations and for situations where neutral genuinely isn’t an option.

Energy monitoring – power use reported to Zigbee

The v2 implements two additional Zigbee clusters that the v1 didn’t:

• 0x0b04 Electrical Measurement – instantaneous voltage, current, and power
• 0x0702 Simple Metering – cumulative energy consumption

In practical terms:

• The SM323 v2 appears as a power-monitoring device in Home Assistant’s Energy Dashboard without any extra integration work
• You can automate based on draw – for example, alert when a bulb fails (sudden drop), or flag a light left on overnight
• The v2 contributes to whole-home consumption tracking
• The same data is exposed in Zigbee2MQTT, ZHA, deCONZ, Hubitat, and any other Zigbee 3.0 hub that reads standard clusters

The v1 didn’t expose either cluster, and firmware can’t add them retroactively – the hardware lacks the measurement circuitry. If energy reporting matters to your setup, the v2 is the only SM323 that delivers it.

No activation delay

Something a few v1 users found mildly annoying: a small delay between pressing the switch and the lights coming on. It was a hundred or two hundred milliseconds – not catastrophic, and many didn’t notice it, but enough to feel a touch less responsive than a traditional dimmer to those who did.

The v2 lights immediately. The hardware has been redesigned and the underlying load-control path changed, and the result is that the v2 feels like a “normal” dimmer in a way the v1 sometimes didn’t.

Works with retractive and standard light switches

The v1 was designed around retractive (momentary) switches – push to toggle, push and hold to dim. That fits most modern UK retrofit installations, but excludes anyone wanting to keep their existing standard on/off switches.

The v2 supports both:

• Retractive (the default) – same behaviour as the v1
• Standard on/off – configurable via Zigbee2MQTT, or activated at the time of purchase by request

This unlocks two installation patterns the v1 couldn’t:

1. Retrofit behind an existing standard light switch without replacing the visible faceplate
2. Two-way installations mixing one retractive and one standard switch

What stayed the same

The v2 isn’t a redesign for its own sake. The things that worked about the v1 are unchanged:

• Trailing-edge dimming – same smooth dim curve, same compatibility profile across LED, halogen, and incandescent loads
• Zigbee 3.0 – same protocol, same hub compatibility (Hue, SmartThings, Alexa, deCONZ, ZHA, Zigbee2MQTT, Hubitat)
• UK back-box compatibility – drops into standard 35 mm or deeper UK back boxes
• Manual fallback – if your Zigbee hub is offline or being updated, the dimmer still works as a regular dimmer at the knob
• Same UK company  – same team, same support, same warranty

If you’re already happy with v1s in your installation, none of that changes. The v2 expands the range of installations the SM323 fits, rather than reinventing the dimmer itself.

Should you upgrade from v1 to v2?

Common situations:

“I’ve got v1s installed and they work fine.”

Don’t rush. The v1 is still supported, the SM107 bypass capacitor is still available if you need one. Replace as and when something else gives you a reason to open the back box.

“I’m planning a new installation.”

v2, no question. The smaller form factor, neutral-wire support, higher load rating, and energy reporting all add up, and there’s no reason to specify the older module.

“I’m getting flickering or ghost-glow with v1s.”

This is the most common reason to upgrade specifically. The v2’s neutral-wire mode eliminates flickering with most low-wattage LEDs. If neutral isn’t available at the switch, the SM107 bypass capacitor still solves it on either generation.

“I want energy monitoring in Home Assistant.”

v2 only. The v1 doesn’t expose the necessary Zigbee clusters and firmware can’t add them retroactively.

“I have a heavy lighting load on one circuit.”

v2. The 350 W rating gives you 40% more headroom than the v1’s 250 W – enough to comfortably drive larger pendants, multi-bulb chandeliers, or longer LED strips that would have been borderline on the v1.

Where to buy (and the v1 question)

The SM323 v2 is the current production model, sold direct at samotech.co.uk and via authorised retailers including B&Q and Amazon UK.

The v1 was discontinued in 2023. If you see hardware that looks like the SM323 v1 listed on a third-party site, or the same module branded under a different name, it may be remaining v1 inventory – old stock that has been re-packaged or re-branded by a third party.

The current, Samotech-manufactured product is unambiguously the v2. Both versions carry the same SM323 name on the casing – there’s no separate part number suffix – but the v2 is identifiable by these visible differences:

• A grey casing (the v1 was a different colour)
• A smaller footprint of 51 × 26 × 24 mm (the v1 is 64 × 27 × 24 mm)
• A maximum load rating of 350 W on the spec label (the v1 was 250 W)
• A live + neutral connector option that the v1 doesn’t have

Frequently asked questions

Is the v1 still supported?

Yes. Samotech continues to answer support enquiries. Support won’t be withdrawn for v1 owners.

Can I have v1s and v2s on the same Zigbee network?

Yes. They both speak Zigbee 3.0 and appear as separate devices in your hub. You can mix and match across rooms without issue.

Will the v1 get Matter support?

No. Matter support is available via the SM323-MT, a Matter-over-Thread variant based on the v2 design. The v1 hardware lacks the radio and processing required for Matter, and can’t be upgraded into it via firmware.

Can I tell which version I’m receiving from the packaging?

Both versions share the same SM323 name on the casing – there’s no separate part number suffix. The v2 is identifiable by its grey casing, its smaller footprint (51 × 26 × 24 mm versus the v1’s 64 × 27 × 24 mm), and its higher 350 W load rating (the v1 was 250 W). All current Samotech stock is v2.

Will Samotech bring back the v1?

No. The v2 supersedes the v1 in every measurable way, and we won’t be returning to the v1 design.