Smart switch listings lead with the per-gang rating: 10 A per channel, sometimes 16 A. Buyers doing bathroom or kitchen renovations read that number, count their gangs, and conclude a six-gang panel delivers sixty amps. It does not. The panel has a second, quieter rating — a total — and the relationship between the two numbers is where real installations either work or overheat.
Two ratings, one enclosure
Each relay inside the switch is a separate switch with its own contact rating, and that is the number on the box. But all those relays share one enclosure, one terminal block, one set of supply conductors, and one thermal environment. The panel as a whole can only dissipate so much heat, so the sum of the channel loads has its own ceiling. A panel might be "10 A per gang" and "total 30 A" at the same time — six channels at full rating would be sixty, and the enclosure cannot live with that. The total rating exists precisely because the enclosure is the bottleneck, and it is the rating least likely to be printed anywhere.
Where the heat goes
Every amp through a relay contact dissipates a little power as heat, and every electronics package adds its own standby heat. In a surface-mount box with air around it, that heat leaves by convection. In the real installation — a recessed metal box behind a glass faceplate, insulated wall, maybe two cables bundled in — the same heat has nowhere to go. Glass fronts are the worst case in the category: they look premium, conduct almost nothing, and turn the interior into a small oven. This is why the same panel that runs cool in a showroom derates in a plastered wall in August.
How derating is hidden
Honest datasheets publish a derating curve: at 40 °C ambient, per-channel capacity drops, sometimes substantially. Most consumer listings publish nothing, and the number that survives into marketing copy is the 25 °C laboratory figure. The practical consequence is that a panel loaded to its printed per-gang maximum across all gangs is already past its true envelope in a hot wall — before you add an enclosure that does not breathe. The failure is rarely dramatic. It is a relay that gets progressively heat-stressed, a touch controller that reboots on hot afternoons, and a panel that dies in its second or third summer.
What this means for real loads
The dangerous configurations are the predictable ones: a six-gang panel where several gangs feed fixed high-draw appliances — water heater, oven hood, underfloor heating loop — while the remaining gangs also carry lighting. Heating loads are continuous, which is the worst profile for a thermally limited enclosure; a kettle draws more but for ninety seconds. The workable rule for a renovation is to distribute: put the heavy continuous loads on their own gang and their own panel where possible, keep mixed panels for lighting-scale loads, and treat the printed total rating as a number to verify against the actual load list, not to assume.
What to ask before specifying
Ask for both numbers explicitly: per-channel rating with the load type it was measured against, and the total rating for the whole panel. Ask whether the total is derated at elevated ambient, and what the derated figure is at 40 °C. Ask what the relay contact material is, because contact material is what survives or erodes under sustained load. Ask for the maximum recommended continuous load per gang, which is a more honest number than the peak. And ask what happens thermally when the panel is at its total rating inside a sealed box — any vendor who has tested this will have an answer.
I work on the manufacturing side of this category, and thermal failures in multi-gang panels are almost always traceable to the missing total rating rather than to bad relays. Our smart switch range lists per-gang and total ratings separately, and our documentation as a smart switch board manufacturer includes the derating data most listings omit. The broader line is at XingLiao and load-planning questions go through our contact page
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