Possibly, but as long as you understand what you've done and that by removing the link cable from whichever convenient extension you used and move the faceplate switch back to 'Copper' you are back to the original state.

"you" who is this, the engineer? or the bodger?

OP: '(My problem is that the master socket was fitted at the far end of my garage, about 50 metres and a complex wiring run away from where I wish the ONT to be sited.)'

The only bodge here is going to be if the OP has to run 50 metres of unnecessary cabling to reach back to the NTE5 when exactly the same result will be achieved using the supplied short flylead from TEL1 into the nearest extension socket.

Actually there might be a second bodge in all of this - BT/Openreach using a bt431a plug and socket in reverse of the designed use (socket is supposed to be upstream of the plug).

In reply to a post by AL66:

the same result will be achieved using the supplied short flylead from TEL1 into the nearest extension socket.

Where is this "nearest extension socket"?

Yes it's just a switch, BUT, if the copper feed goes to an original NTE elsewhere, and the 'new' NTE is on an extension then the switch of the interstitial plate won't be disconnecting your extension wiring on it's path back to the original feed.

In reply to a post by Zarjaz:

Yes it's just a switch, BUT, if the copper feed goes to an original NTE elsewhere, and the 'new' NTE is on an extension then the switch of the interstitial plate won't be disconnecting your extension wiring on it's path back to the original feed.

I think you are misunderstanding me - the NTE5 stays where it's always been (in the garage) complete with new faceplate isolating the internal wiring from the incoming copper line. Only difference is the flylead is plugged into whichever extension socket is convenient for the ONTE position rather than the NTE5 faceplate.

What if the NTE is the most convenient for the ONT ?

Apparently, it's not what with being 50 metres away in the garage.

In the 'correct' setup the feed from the ONTE via the fly lead should terminate on the rear of the interstitial faceplate.

I do FTTP installations on a regular basis.

OK - interesting to know, are there IDC connectors on the back of the FVA SSFP? Picture would be good! Andrew has some pictures of the faceplate but not the back.

P9 of the Fibre Developers guide shows a picture of 'Interconnecting voice lead (Item Code 77004)', cable with a standard looking phone plug on both ends. I guess with a new build there's going to be no copper - possibly just a string of developer installed slave sockets which use that cable to connect to one of them.

Still don't think the standard way of doing it is going help the OP though - simpler solution will be use the FVA faceplate to isolate the incoming copper and then use the flylead as described as if a new build.