BT Signalling Unit 101A

From the BT User Instructions….

The unit provides the following ports:-

1. Line Interface port (2w or 4w)
2. Customer Interface port (2w or 4w, E+M and sig earth out and Signal rail in)
3. Power supply port, my rack was locally powered by the usual -50v and 0v power.

From the manual, this is one way the unit was intended to be used:-

Manual:- sigunit101a.pdf