If you are connecting only one device to your BRI NT1, the cable can be as long as 1 km if you are using Category 5 twisted pair.

In practice, if you really need to run a cable for this distance it would probably be safer to re-site your NT1 closer to the equipment to be connected.

All NT1s have two sockets for devices, so you could add another device to the other socket at a similar distance.

This form of wiring is known as point-to-point.