Smart switch installs mostly fail at a point nobody thinks about: the last few millimetres where the wire meets the terminal. The switch works, then doesn't, and the problem is neither the switch nor the wiring design.
Two separate ratings meet at one point
A cable has a current rating based on its conductor size and how much heat it can shed. A terminal has a current rating based on how much contact area it can maintain and how much heat it can dissipate in a small plastic enclosure.
These are different numbers decided by different things. A terminal rated generously for the current you are switching can still be the weak point, because what matters there is contact pressure, conductor type and how the joint was made — not the ampacity of the cable feeding it.
Why stranded wire behaves differently
Many terminals are designed and tested with solid conductor. Flexible stranded cable of the same nominal size behaves differently under a screw: the strands move, the bundle compresses, and the contact area you actually get depends on how well the strands were captured.
Over time, and with the heating and cooling of daily use, a compressed strand bundle relaxes slightly. The screw is still where you left it. The contact pressure is not. That is how a joint that was fine on day one becomes the warm point a year later.
This is why the same switch can be reliable in one house and marginal in another with identical loads: different conductor, same terminal.
"Tight" is not a measurement
Screw terminals are usually tightened by feel. Too little and contact resistance is high. Too much and you can deform the conductor or the terminal itself, which also reduces contact quality.
Neither failure is visible. Both look like a properly finished installation.
Several conductors under one screw, or a conductor plus a loop of another, is the case that goes wrong most often: the screw can be pressing on one of them and barely touching the other, and it will never look wrong from the outside.
The enclosure changes the budget
A mechanical switch sits in a box and dissipates almost nothing. A smart switch dissipates a small amount continuously, all day, regardless of load.
That heat is inside the same enclosure, next to the terminals, behind a faceplate. So the terminals are operating in a warmer environment than they would be in a dumb switch, with less margin for the extra heat that a slightly resistive joint produces.
The failure mode is slow, then sudden
A resistive joint does not stop working. It warms, expands, loses a little pressure, warms more. It can run like that, apparently fine, until a load increase or a hot week moves it into a different regime.
Smell, discolouration, a faceplate that is warm, or a light that behaves inconsistently when something else switches on, are all late signals.
What actually helps
Match the conductor to what the terminal was designed for, and use the termination method the manufacturer specifies. If stranded cable is going into a terminal intended for solid conductor, the fix is the correct ferrule or the correct terminal type, not more force.
One conductor per terminal unless the terminal is explicitly rated for more.
Treat any warmth at a switch as information about the joint, not about the switch. Re-tightening a joint that has already been hot rarely restores it — a contact that has degraded has changed surface, and the usual outcome is that it degrades faster from there.
And when a smart switch behaves intermittently in a way that moving or touching it changes, look at the termination before looking at the radio.
Where this matters when you are buying
Check the hardware first: smart switches.
Panel standards, protocols and MOQ live on the Xingliao smart home factory site; panel families (86, 118, 147) are on the smart switch board manufacturing page. Sourcing questions go to the factory team.
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