A code of letters is used to name the symbols on plans. The designation consists of three parts:
Numerical Prefix which gives the number of the unit concerned.
Prefix Letter which denotes the purpose of the unit.
Final letter which denotes the kind of unit.
The complete designation is written thus:
10TR - 10 track relay.
10TPR - 10 track repeating relay.
74RGKE - 74 stop signal indicating lamp.
Description Term (prefix letter)
A. Approach; automatic
B. Block; Bolt
C. Checking or proving
D. Clear, (green); 90 degrees
E. East; Heat
F. Fog; flashing
H. Caution, (yellow); 45 degrees
J. Time element
K. Indicating or detecting
L. Locking; left
M. Marker; magnetic;
N. Normal, north, slow release
P. Repeating; power
PC. Pole changing
Q. Treadle or bar
R. Reverse; Right; Danger (red); 0 degrees
T. Track ciruit
U. Route (aspect displayed to be shown in brackets)
V. Train stop
W. Points; west
Y. Slotting or disengaging.
Z. Special (to be explained on plan)
Up. Up (direction of traffic)
Dn. Down (direction of traffic)
Apparatus (last letter)
A. Elecrolytic cell
B. Block instrument
E. Electric lamp; earth
F. Fogging apparatus (e.g. detonator placer)
G. Signal apparatus, including light signals
g. Lightening arrestor
H. Condensor; capacity
K. Indicator (visual)
N. Release; Hand operated switch; push button or key
P. Lever latch or trigger contact
Q. Local coil of double element relay
R. Relay or contactor
S. Stick relay
U. Train description apparatus (for route indicating)
V. Train stop apparatus
W. Points, operating apparatus
X. Audible indicator (such as bell; buzzer; horn)
Y. Disengaging apparatus
Z. Special unit (to be explained on plan)
Last Updated: Sat June 8 2013