Good day everyone, I have a small problem with a relay: When I switch the relay with my Arduino without 230 volts, everything works perfectly. However, as soon as I use 230 volts, I can only close the relay. As soon as I open it, the Arduino (RX) crashes. Thanks for Help!
You need a back EMF filter. A simple diode for DC, much more complicated for AC.
I was not aware of that particular model of Arduino. Can you post a link to its specs?
Start by reading the forum guide in the sticky post at the top of most sections of the forum.
Which, for example? It's AC Current
Its an Arduino NANO, i found in an Chest
What you have powered at 230V?
You might need snubber. And keep your "arduino wiring" far from your 230V load wiring.
I had a little 230V Motor with around 4 Watts running 7 centimeters away from the "arduino wiring". It can't go wider, cause i have space issuses.
That's not a lot of distance...
Important, that the 230V wiring doesn't run together (parallel) with arduino wiring.
And add a RC-snubber.
Hi and welcome to the Arduino forum 
You inspire a lot of questions:
Where did RX come from? Arduino (RX)
What hardware are we talking about here. No, not interested in hearing it's a relay etc, but what relay do you have. Serial nr is not needed, but anything up to that. + the rest of the setup.
Why an Arduino for the job, or any other MCU for that matter?
Are you knowledgeable in working with mains voltages?
While at it, a schematics / diagram will be VERY helpful. Unless you like spending a lot of your and our time.
Hi, The RX comes from an MAX485 Module to 'decode' an DMX signal. The relay is an " SRD-05VDC-SL-C" The (5V) power comes from an external Power suply.
Here is the diagram:
I don't have much knowledgeable with mains voltages, but i show my work to people which have.
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Relay module?
yes
Add snubber and switch line with relay, not neutral.
Datasheet tell the relay coil uses 71.4 mA. I wonder how much an Arduino can supply from an IO pin..
Are we talking about a module here, or just the relay? If it's just a relay, you should get a diode in reverse, parallel to the coil, for protection or your IO pin will not be an IO pin anymore soon.
Edit: Above have been answered.
You mean i should add the Relay Module directly to the Power supply (current all of the 5V Consumers are directly connected to the arduino) or what?
Where I live it doesn't matter, but might do where OP lives. So where does OP live?
In germany
where i have to add the snubber?