The most confusing electrical failures are the ones where every individual number is inside its rating. Each device is fine, each socket is within its limit, and something is still heating up.
Where the limit actually sits
A smart socket has a current rating, and it applies to what flows through that socket. When you plug a power strip into a smart socket, everything downstream flows through the smart socket's relay and contacts. The strip has its own rating, and each appliance is within that, but the smart socket is now carrying the sum.
No single device is overloaded. The first socket in the chain is carrying all of them.
Why the first point fails first
Every connection has a small contact resistance. It is tiny and harmless at low current. Heat generated at a connection rises with the square of the current, so doubling the current quadruples the heat at that point.
That means the warm spot is not where the load is. It is at the weakest junction carrying the whole load — usually the plug-to-socket interface at the very front of the chain.
Stacking connections multiplies the problem
Each plug-in connection is another contact pair with its own resistance. A chain of them does not share the load evenly; each one carries everything behind it while contributing its own resistance. A slightly loose grip, a worn socket, or a plug that was never fully seated adds more resistance than any of the ratings account for.
This is why daisy-chained connections are treated with caution out of proportion to the load. The issue is not the total current. It is the number of series contacts it passes through, each one a small heater.
Why a smart socket is a different case
A smart socket contains a relay. That relay has contacts designed for a specific current and load type, and it sits inside a small sealed plastic enclosure with limited ability to shed heat.
Running the relay near its rating continuously, in a warm enclosure, behind a sofa, is not the same duty cycle as switching a lamp for an hour. Continuous load deserves more margin than intermittent load, and the label does not say so.
There is also a switching element that dissipates a little heat of its own, all the time, regardless of load.
Why nothing trips
Protection in the consumer unit is sized to protect the wiring in the wall, not the plug-in devices at the end of it. A socket can be comfortably overloaded in its own terms while drawing far less than the circuit breaker's rating. The breaker will not save it.
This is the core of the confusion: "the breaker did not trip" is not evidence that the arrangement was acceptable.
Why the heat is intermittent
Contact resistance changes with temperature. A connection that warms expands, the grip relaxes slightly, resistance rises, and it warms more. Under a continuous load this settles into a hotter steady state rather than a failure — so it can run warm for months and then become a problem when the load increases or the room gets warmer.
A smell, discolouration, a socket that is warm to the touch, or a plug that comes out hot are all late signals. None of them are things to keep monitoring.
What actually helps
Add up the real load behind the first socket, not the load of the nearest appliance. The relevant number is the total on that chain.
Keep the number of series connections low. Fewer plug-in joints means fewer points where contact resistance can develop.
Give continuous loads real margin. Anything running for hours — a heater, a dehumidifier, a pump, a server — should sit well below the printed figure, and ideally on a connection designed for it.
And if a socket or plug is warm, retire it. Heat at a connection is a property of the connection, not of the appliance, and no amount of load redistribution fixes a contact that has already degraded.
Where this leaves you
If you need more outlets, the safe answer is one properly rated socket in the wall rather than stacked adaptors behind it.
The range we build for this sits here: smart plugs and sockets
I work on the manufacturing side of this category, so read the above as opinionated rather than neutral. If you want the datasheets instead of the argument, they are on XingLiao Tech.
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