You can find more information about the facts of the case at https://wiki.mikrotik.com/wiki....

The problem with overheating occurs with almost all passively cooled solutions on the market. Unfortunately, not everything about Mikrotik is always described conclusively on the product page. The target group is clearly the professional low-budget market. Therefore, it is often assumed that the customer knows his way around. This is not always to the benefit of the brand.

The fun starts with the fact that with SFP+ solutions it always depends very much on what kind of modules are used. Old 10 Gbit/s copper modules of the first generation had up to 12W of waste heat. It is almost impossible to dissipate this passively. The waste heat arises because with 10 Gbit/s the switching times are very high and therefore the switching losses of the control electronics increase immeasurably. The longer and worse the cable, the more unpredictable (large capacities, resistances and inductances). According to the manufacturer, the Mikrotik S+RJ10 modules require 2.7W for 30m of cable. The specification of the mentioned switch specifies a maximum of 8W for the 4 modules. Equipped with 4 copper modules, one would therefore theoretically already exceed the limit. Please do not connect 100m of cable per module. At the end of the page linked above, it is also clearly stated that you have to provide additional cooling for passive switches if you do not leave out a slot between the modules. Experience shows that it is usually possible to place an optical module in between, which normally only requires 0.4 to 0.8W for up to 300m.

As Thomas has already written correctly, in this case either active cooling is necessary OR you switch to optical modules (fibre optic multimode) OR you use passive or active DACs (Direct Attached Cable). The last option is by far the cheapest, if you can design the cabling accordingly.

Multimode module: https://mikrotik.com/product...
Passive DAC: https://mikrotik.com/product... (1m)
Active DAC: https://mikrotik.com/product... (5m)

Once you get the hang of Mikrotik, you really get a lot for your money. It may take a little while until it's ready ;-)

Hello Acaillet

Yes, I also have this Switch model and yes, mine got hot too.
See also the other questions and answers here.

It also depends on how you equip it!
According to Mikrotik, only 2x RJ45 transceivers are supported.
https://wiki.mikrotik.com/wiki...
-> "CRS305-1G-4S+ -- supports up to 2 simultaneous S+RJ10 modules."
- I would then use these 2 in slot1 and 4.
But only optical transceivers would be best. These stay cool and don't even get "hand-warm"!
I use optical interconnects and DAC cables. (Sorry digitec, but tip: the Bra... has a better selection and availability).

And I also have a 120mm fan above the whole unit... since then everything is fine. :)
But after a while I switched to the 8-port model because of the lack of ports.

Greetings
Thomas