Create a single page with 3 Lines of Voltage L1,L2,L3 between 0 and 300 V

Perhaps you can show us a picture of this?

An export of your flow and a sample of the data would help too. Please don't post these as pictures or we won't be able to work with them.

In order to make code readable and usable it is necessary to surround your code with three backticks (also known as a left quote or backquote ```)

``` 
   code goes here 
```

See this post for more details - How to share code or flow json

There’s a great page in the docs (Working with messages : Node-RED) that will explain how to use the debug panel to copy any data item.

Pay particular attention to the part about the buttons that appear under your mouse pointer when you over hover a debug message property in the sidebar.

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