I am due to get broadband fibre connection soon and want to connect the ONT to my router through a short underground conduit which has a 7kw EV supply cable. The overall length is about 20 meters. Should I make this connection with a LAN cable or consider a fibre optic extension? I have read that a LNA cable very close to a power cable can cause interference problems.
I wouldn't worry so much about the interference, if I were you.
I'm not an expert here, but at that voltage I'm pretty sure putting them though the same duct would break all sorts of health and safety rules, some of them probably legally enforceable. (Even at mains voltage, I seem to recall you need a minimum of 2" separation).
If you are running low voltage or Ethernet alongside a 7kw cable the shielding of the low voltage or Ethernet cable must be rated to the same as the 7kw cable. This is in case of arching from the 7kw to the Ethernet cable which would pose a fire risk or as has been stated by @WSH the cables must be separated either by 50mm distance or 25mm if in a separate duct within the duct.
As the ONT doesn't have an optical output your choice is limited unless you employ a converter at each end.
Voltage hasn't been mentioned, I assume it is just standard domestic 230v supplying an electric vehicle charger.
@licquorice Good point. I read it as 7kV, but even 7kW is a lot of current, (30A).
Indeed
Thanks for all the comments - sounds like a LAN cable in the same ducting is not the right way.
Perhaps need an optical cable with a converted at each end!