A.T. - Automatic
B.E. - Branch Exchange
C.B. - Common Battery
C.B.S. - Common Battery Signalling
D.C. - Double Cord
F.P. - Floor Pattern
L.B. - Local Battery
N.T. - National Telephone Co.
S.C. - Single Cord
T.E. - Telephone Exchange
W.P. - Wall Pattern
How P.M.B.X.s are described:-
They are described by the main circuit diagram followed by a fractional
suffix representing Equipment/Capacity.
E.G. Switchboard CB 873
CB 973 is the main circuit diagram.
3+10 is the equipment/capacity of 3 exchange lines and 10 extension
25 is the ultimate total capacity of 5 exchange lines and 20 extensions