Shelly 2.5 getting hot to touch (63°C external case) - should I be worried?

I have just started experimenting with a Shelly 2.5 WiFi switch for controlling LED downlights and currently just have it sitting on a bench connected to two 8W downlights (one on each output) which are also sitting on the bench about 1m away.

The Shelly case is getting hot and I’m concerned about putting these in my wall cavity. They have an internal temperature sensor and I read on the Shelly FB page that they will automatically switch off at 90°C.

With no load (both lights off) it sits at around 58°C as reported by internal temp sensor.

With both 8W downlights on, the Shelly reports 86°C after a couple of hours. Using a non contact infrared thermometer, the outside case is at about 63°C - this is quite hot to touch. I note that the LED downlight (also sitting on the bench) is about the same temperature, and this is meant to mount in the ceiling with insulation nearby.

I believe the heat is due to the current sensing circuitry, and also the processor runs warm. Shelly say it’s UL underwriter certified and made from fire proof plastic, they reckon it would eventually melt but not catch on fire.

Does anyone on here have any knowledge in this area? How hot is too hot to put something like this in the wall cavity, or am I worrying unnecessarily?

I’d be VERY worried !

Internal temperature is one thing and some devices are designed to ‘accommodate’ some high temperature components. But for the case to reach 63°C is extreme. 70°C is the design limit for cables following short circuit protection both for the resistance rise with temperature and for the life/durability/insulation capacity of said cables. (adiabetic (damn auto correct) adiabatic calcs)

How do you have this wired ?
Have you followed the manufacturers guidelines ?

I have it wired as per manufacturers guidelines. It’s very simple (I am an electronic eng :slight_smile:)

What I hadn’t measured was the ambient temp. Since my post I’ve done some more research. The relevant safety standards are about rise above ambient, specifically, above an ambient of 40°C. See this article.

IEC61010 has the following limits for plastic items (Shelly has a plastic enclosure). I chose the IEC61010 standard as Shelly is rated to a max ambient of 40°C:

  • Plastic, unintentional contact: 85°C (a rise above ambient of 45°C)
  • Plastic, knobs and handles : 70°C (a rise above ambient of 30°C)

I would put Shelly in the “not intended to be touched category” (vs a kettle handle, or oven handle for example). I am guessing my garage was at about 28°C when I did the measurement, this would give a rise of 63-28=35°C so easily meets the standard. I will re-measure two shelly 2.5’s today, including ambient and report back.

Here’s a couple of screen grabs of the above article and a photo of my test setup.


I repeated the temperature testing of the Shelly 2.5. It was cooler in my garage today so the figures are a bit lower than yesterday.

No load, Ambient 25°C
Measured external case temp = 47°C = 22°C above ambient
Internal temp sensor reports 58°C = 33°C above ambient.

Load of 2x 8W LED down lights, Ambient 25°C
Shelly 2.5 has two outputs, connected one 8W downlight to each output
Temperature stabilised after about 1.5 hours (see screen grab)
Measured external case temp 57°C = 32°C above ambient (well below the 45°C allowed by IEC61010)
Internal temp sensor reports 72°C = 47°C above ambient.

Obviously this is limited testing using a thermometer with ±2°C accuracy. And it should really be done at full rated load of 10Amps (maybe it would fail the temp rise limit then), but I’m more interested in LED downlights.

So with an LED downlight, if the inside of my walls could reach 40°C (unlikely but possible), then the external case would reach about 40+32=72°C. And the Shelly internal temperature would be 40+47 = 87°C, still below the 90°C at which point the Shelly will automatically turn off.

I also measured the downlight temperatures too, with the following results:

Brilliant smart WiFi LED downlight (the one on the left hand side in photo above), at full brightness after 1.5 hours, measured 61°C, temperature rise above ambient of 36°C.

Arlec dumb LED downlights (the two I used to load the Shelly, on the RHS), full brightness after 1.5 hours, measured 55°C, temperature rise above ambient of 30°C.

Not sure what to make of all this, it seems that the Shelly 2.5 easily meets the IEC61010 standard, and the LED downlights themselves are putting out similar levels of heat. Maybe I just need to accept that we regularly put “hot to the touch” stuff in our houses?

It’s a pleasure to read someone who a) understands the concerns b) has a testing plan c) carries out that plan in a logical consistent manner d) has read up on the relevant standards

I can’t fault anything you have done.

My first thought was that you should ‘wrap’ these devices to protect from accidental contact BUT that would just keep the heat in so DON’T do that.

My second thought was “what do my dimmers run at” I use fibaro z wave dimmers and I took the switch face plate off, moved the switch to get at the dimmer, it was cold (ambient) which is what I expected for off. On full power (I only left mine 40 mins) it was moderately warm but easily not warm enough to cause any concern (touch is my only test method at the moment but the central heating runs at 65 C and it was nowhere near that, exit pipework) so then I ran it (40 mins) at 70% (as that should be about wosrt case) it felt a bit warmer (subjective or piling on from the last test ??? ) but still not hot enough for concern.

Two things strike me, 1) the spiders in your service spaces are going to have a toasty place to live. 2) How much energy are you throwing away in heat ?

Maybe these are acting within specification but I would not buy these or use them if I had any choice.
You will have to assess each usage case and installation scenario to determine if you are happy, your approach and methodology tells me you will make the right choice.


  1. Bulbs have always been major heat sources gu10 types especially.
  2. LED ones run a lot cooler than their predecessors so a move in the right direction (but can still be surprisingly “warm” ).
  3. I couldn’t work out why the gorilla pod was there, then I saw it was a metal filing cabinet. I usually steal a glass shelf off the cooker hob (Ikea halogen cover) or a wooden chopping board. 4. Accidental cable movement can cause unfortunate stains in your underwear or worse destroy the kit you are testing
  4. I notice the devices bear both CE and RoHS markings and your sockets indicate you are in Aus or NZ so it “should” be compliant. (I know you know this).

There is a thread here on “electrical kit certified for use in Aus/NZ” I suggest you search for that and have a read, though it is a LOOONNNGG read :rofl:

Good Luck, Happy Automating

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Situation: The temperature of a lightly-loaded (just 3 LED lights) Wi-Fi controlled relay rises more than 35°C above ambient temperature.

First-order analysis: it’s either defective or there’s a design flaw.

I have several wall-mounted Wi-Fi switches, all lightly-loaded, and they get barely warm to the touch. I have many more wall-mounted UPB switches (not RF-based) and they too get barely warm. In contrast, a case temperature of 65°C is substantially more than barely warm.

FWIW, the device may ‘fall within specs’ but compared to other choices, it runs hot.

maybe someone can compare Shelly1 to Shelly2.5?
Temp grow of Shelly1 working without load is not recognizable with naked finger. Shelly2.5 is significantly warmer. I don’t know which part of shelly circuit is responsible for this. Maybe it’s related to current/power measurement (?)

I have a few Shellies in use. This is what they report as their internal temp:

Shower Fan and Light (combined) SW0 and Nightlight SW1
Ambient: 69 F / 20.56 C
Shelly 2.5 no load in 3-gang box with plenty of spare room: 110.8 F / 43.78 C

Toilet Exhaust Fan and Light (combined) SW0 and Nightlight SW1
Ambient: 69 F / 20.56 C
Shelly 2.5 no load in 2-gang box somewhat cramped: 123.1 F / 50.61 C

Ambient: 60 F / 15.56 C
Shelly 1PM no load: 99.5 F / 37.5 C

Hope that helps.

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ok my post is long, but it was actually a separate downlight (Brilliantsmart) that rose 36 above ambient.

I also tested the Brilliantsmart smart dimmer mech, and some other Wi-Fi switches, and same as you, they barely get warm.

But to your other comments, I tend to agree, the bottom line is it runs hot on a light load (2x LED downlights) and even if it complies with a standard, I’m not comfortable with it.

exactly, this is why I started investigating Shelly 2.5 as it was noticeably warmer to the touch. I believe it is a combination of the CPU and currnt/power measurement.

Thanks @Mutt appreciate that. I also have some Fibaro z-wave dimmers / switches which I should test.

Maybe these are acting within specification but I would not buy these or use them if I had any choice.

I agree, this is basically my conclusion. Problem is I don’t want to battle with z-wave any more, so trying to find a Wi-Fi equivalent.

I’m also aware Shelly are not certified for Australia, but there aren’t many options. There are some Zigby devices new to the Australian market, I might get some and test them. I just really like the responsiveness of Wi-Fi. I wonder if Zigbee is as good once you have 20+ devices.

The gorilla pod was there to lift the Shellys up off the cabinet for airflow, like they were hanging in my wall space. BTW the cabinet is Ikea and made of wood, not metal! I wouldn’t put this rig on a metal cabinet :slight_smile:

Yes I read the Aus/NZ certified thread very often!

I’ve just installed a Shelly 1PM to control a 3.1kW immersion heater. overnight run when the Octopus Go rate is only 5p/kWh (cheeky referral link). It’s sitting in a large single-gang back box behind a single UK socket.

I’ve only just set up the internal temperature sensor as a Home Assistant sensor, so we’ll see how hot it gets after the overnight run. From a short test, it looks like it’ll approach 75°C at ~13A. It’s sitting at 47°C switched off in the ambient of a warm airing cupboard, probably about 28°C.

That’s hot.

To serve as a point of reference, for over ten years I’ve used an X10 Heavy Duty Relay Module to control my 220VAC 1.5 HP pool pump motor. It’s CSA approved, rated to handle 20A, and has run reliably for over ten summers. It barely gets warm to the touch.

If a device meant to just turn on a load runs so damned hot (75°C) then it’s the wrong tool for the job.

When I get home from work, the engine is burning hot, yet I can touch the hood without any pain. The shelly sensor measures temp of the PCB, not the outside of the case. 70C isn’t too much for a PCB in general, but depending on the thermodynamics at play inside the case, there may be nearby components that have lower temp ratings. What are those ratings? Even cheapo electrolytic caps usually are ok to 85C. YMMV, but bottom line is if you flash a even a UL listed shelly, they’re not going to be liable if your house burns down lol.

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If you’re going to use a car as an analogy then let’s do it right. Use a stock passenger vehicle pull a large house-trailer from Denver up into the Front Range while maintaining at least 60 mph. Then return to Denver. Let’s see how its transmission, cooling system, and brakes handle that.

The Sonoff behaves just like that passenger vehicle. It can do the deed but not without suffering. For heavy-loads, a purpose-built vehicle is the better choice (or, in this situation, a device with a robust relay).

My “barely gets warm to the touch” reference was a shortcut to saying the internal operating temperature of this sealed device (X10 relay) is so low that it’s case barely gets above ambient (and that’s not due to any insulation like on the underside of a car’s hood or assisted convection-cooling like in a moving car).

That passenger car trailer analogy would be closer to running a stick welder off a shelly, not some new led bulbs. Anyhow, I agree that the tool has to fit the job. The shelly’s are not rated for big amps though, and they do fine within their rated specs. If we needed to switch a 20A load, yeah the shelly probably isn’t a great idea, but that would be no different than running 14awg to a 50A breaker… no electrician would install it like that, and hopefully no DIY’er would either.

[edit: Note that shelly 2.5’s are only rated to 10A (per output)… lol when calibrating mine I went way past that. However installed, the biggest draw I’ve got on a shelly 2.5 is 700W. Even then they do heat up a little bit… definitely not the same hunk of meat as an industrial relay, with the power monitoring resistor and whatnot inside, and a super insanely compact PCB that can’t have much copper area.]

User Troon is running a continuous 13A through a self-certified device rated to 15A. That’s 87% of its maximum load for a device that self-destructs at or near its rated maximum (see image in first post and in related topics about melting Sonoffs). The car hauling a heavy load isn’t too far off the mark, with the exception of turning itself into a molten blob.

If Sonoff wired a house, they’d do it without fuses or breakers, use 16 gauge wire, and claim everything is (self) certified to 15A and 90°C. Not to worry if the house wiring runs hot because, hey, it’s rated to 90°C.


Trug, read the top of this thread where patfelst did tests measuring the external temperature. So there is no ‘hood’ to protect your wittle fingers from the incandescent dwiving thingy.
The devices are pretty tiny anyway so actual insulation is negligible.

17 minutes running my 1PM at 12–13A (depending on line voltage) last night. Looks like “terminal internal temperature” would be around 82–85°C if run for long enough, just going by the shape of the graph.

Worth noting that the Shelly’s relay remains on until 04:25 but the immersion 'stat has opened at roughly 04:02, cutting the current. You can see the cool-down temperature gradient steepen after 04:25 when the Shelly relay also shuts off.


By self destruction, you mean an internal temperature of 85C? Also, I can’t seem to find that image of a melted Sonoff in this thread or related topics. I don’t doubt that there are pictures of burned up sonoffs, or pictures of burning fire extinguishers on the internet. I’m not trying to an arse here… if it comes off that way, I’m just pushing for the truth.

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