strange thing happen here.

Hi
I have a working home automation with arduino mega, rtc, relayboards, 4ch dimmer, ethernet shield, push buttons, led bulbs and 2 rollershutters. When disconecting neutral/line from the 2 roller shutters, everything works fine. When connecting neutral/line from roller shutters to relayboard arduino does weird things like opening shutter when not asked, put on lights when using shutters.
Now i used a second arduino mega, relayboard en ethernet shield for only shutters ans still same sh*t. when only using rollershutters whithout other arduino, it wordks fine....
Anyone has an idea how to make this work?

You need to make a drawing showing how everything is connected and post a photo of the drawing.

...R

When disconecting neutral/line from the 2 roller shutters, everything works fine.

It sounds like you have a ground loop in the AC line. That is, the neutral wires are not at the same potential, which can be a very serious problem.

You cannot power the Arduino from a (computer on a) different branch of the AC circuit than the roller shutters. To diagnose the problem, run the Arduino from a battery supply or a laptop not connected to the AC line.

If your neutral wire is grounded (earthed), I wouldn't break it with a relay, only the "hot" wire.

Neutral not earthed here.
Main voltage is 3 x 220.
I have 3 different switches in main board:
1 for automation, 1 for lights and 1 for shutters.

You're putting 380V across those little relays? Could you post a link to the relay board?
So you have 3 phase 220V delta connection? Is one of the phases grounded?

No grounded phases.
circuit 1, phase 1 & 2 = 220V
circuit 2, phase 2 & 3 = 220V
circuit 3, phase 1 & 3 = 220V

To diagnose the problem, run the Arduino from a battery supply or a laptop not connected to the AC line.

No grounded phases.
circuit 1, phase 1 & 2 = 220V
circuit 2, phase 2 & 3 = 220V
circuit 3, phase 1 & 3 = 220V

That would be a serious code violation for household wiring in most countries. You SHOULD have a neutral lead similar to that shown below.

Here at home i only have 3 phases, 3x220V, no neutral.

Then it would be a very bad idea to connect two devices powered by different branches of the AC supply, as you have apparently discovered.

Can you explain what you actually meant by "neutral/line" in the original post?

When connecting neutral/line from roller shutters to relayboard arduino does weird things like opening shutter when not asked, put on lights when using shutters.

You are saying contradictory things in different messages:

When disconecting neutral/line from the 2 roller shutters, everything works fine.

Here at home i only have 3 phases, 3x220V, no neutral.

You need to clarify with a good diagram, its just confused otherwise. Say what country too...

Country is belgium but the problem is fixed.
I changed de sketch to use DEBOUNCE with the buttons, every works fine … for now.
Sorry for my bad english.
thnx for replying.

Just so that we are not as confused as the OP:

The household wiring standard for Netherlands/Belgium is three phase with neutral and protective ground.

Three phases:

N - Light Blue - Null / Negative
L - Brown - Phase / Positives
L2 - Black or Brown - Phase / Positive
L3 - Grey or Brown - Phase / Positive
T - Black - Switch wire
⏚ - Yellow/Green - Protective earth / ground