The four-gang touch panel looks like four independent switches sharing a faceplate, and the specification sheet reinforces that impression by printing the same rating under each button. Electrically, that rating is measured one relay at a time on a bench at room temperature. Thermally, four relays live in one sealed box behind a glass panel, and heat is a shared budget. Loading every gang to its printed maximum at the same time is the classic way to turn a correctly rated product into an early failure. Understanding the derating logic matters when choosing smart switches for kitchens and utility rooms.
Heat is the budget
Every relay has contact resistance, every switching element has on-state resistance, and the power those losses dissipate turns into heat inside the wall. A single gang carrying ten amps may dissipate a watt or two — trivial when it can conduct through a metal frame and the surrounding air. Four gangs carrying ten amps each produce four times the heat in the same enclosed volume, and the temperature rise is roughly additive. Component lifetime falls steeply with sustained temperature, and every ten-degree increase roughly halves the life of the electrolytic parts nearby.
Ratings assume a cold neighbor
The printed per-gang rating is validated with the other gangs idle. Standards and honest datasheets acknowledge this with a total capacity figure or an ambient temperature note — the rating holds at 25 °C, and above it the allowable current drops. A panel running four loaded gangs sits well above ambient inside the box. Quality manufacturers publish a total switching capacity for the unit, which is the number that reflects reality. Where only per-gang numbers appear, a practical rule from panel builders is to treat the sum of continuous loads as roughly 60 to 70 percent of the sum of the printed ratings.
The glass panel is a heat trap
The tempered glass front that makes touch panels look premium is a poor heat conductor compared with the aluminum faceplates of old mechanical switches. Heat leaving the device mostly flows backward into the wall box and the wiring, not forward through the glass. A shallow plastic box buried in insulated plaster traps more heat than a deep metal box in a hollow wall, which means the same switch runs hotter in two different houses. Installers see this as random failure luck; physically it is enclosure physics.
The box behind the panel matters
A crowded back box compounds the problem. Good practice leaves the box to the switch and little else, but retrofits often stuff the box with wire nuts, folded conductors, and sometimes a second device. Every extra item displaces the air that carries heat away and adds its own small losses. Deep boxes, clean conductor dressing, and refusing to share the box with dimmer modules cost nothing at planning time and buy years at load time. For high-load rooms, splitting loads across two physically separate panels — two gangs in one box, two in another — restores full per-gang capacity.
Realistic loads rarely collide — until they do
In a bedroom, four gangs of LED lighting never approach any limit. The risk lives in specific rooms: the kitchen where gangs feed an extractor, under-cabinet lighting, a disposal, and a water heater booster; the utility room with a dryer circuit; the bathroom with heated floors, towel rails, and fans. Kitchens and utility spaces are exactly where people buy four-gang panels, which makes the derating math non-optional. Adding up nameplate amps before ordering the panel takes five minutes with a phone calculator.
What a datasheet total means
When a specification lists both a per-gang rating and a total rating, the total reflects the thermal design of that specific panel — relay placement, copper area, back-plate materials, and the housing. Two products with identical per-gang numbers can differ meaningfully in total capacity, and the difference is engineering, not marketing. Buyers sourcing panels for humid or high-load markets can ask manufacturers for the thermal test conditions behind the figures; the smart switch board programs publish derating context for exactly this reason.
Questions for the supplier
Ask for the total continuous capacity of the panel with all gangs live, and the ambient temperature the rating assumes. Ask how the panel behaves when one gang runs at full load for hours — is the relay rated for that continuously or only for switching duty? Ask about the recommended back box depth and whether the warranty assumes it. These questions take one email, and the answers separate suppliers who tested the product from those who assembled it. More platform documentation is available at Xingliao, and volume buyers can open technical discussions on the contact page.
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