Factorio Forums

Put simply, a special type of pole that can be turned on and off. Perhaps with conditions. That way you can put these switches in key locations to isolate/disable areas of your network in a less complex fashion than currently exists when you need to.

This has been sugested several times already.
Develoipers did expressed an option to implement this but they didn't say when. So all we have to is wait for them to implement this or for someone to make a mod for this.