Shore Line Junction (SS81)
US&S B30 Local Control panel from the NYNH&H Railroad
Local Control Panel restored and operating (note traffic arrows)
Builders Photo of Panel (1956)

This, and many other panels like it, were located
at the remote interlockings around the New Haven
station. In the event that the SS75 NX machine that
controlled them failed, the local panels could be
activated with a key and maintainers could run the
interlockings manually to keep trains moving.
Here are some pictures of the SS75 NX machine:
And a close-up of Shore Line Junction:

The New Haven SS75 NX machine used the Union Switch & Signal 516-A Multiplex Code Control System,
which used high-speed radial (RD) relays and ran at 25 steps per second ...
much fast than the usual 3-4 seconds per 16 steps with older code systems.
It could register 25 two-position control functions and 50 two-position indication
functions simultaneously per second.

The line circuit was either over two-wire carrier (using 4 frequencies) or 5-wire DC line circuits.

This system was meant to control a single, large plant from a remote location.
These pictures are dated 11-3-1954 - from the New Haven.
Office Code Rack
Field Code Rack
Test Code Rack
Office and field racks are made up of the following relay components:
Office Coding Unit
Field Coding Unit
Chain Unit
(for both office and field)
Click here to listen to the chain unit stepping thru 32 steps in real-time for two code cycles.
- or -
Click here to listen to the chain unit slow stepping thru 32 steps in slow motion.

The above sound files were created with this chain unit from the New Haven.
I am using a Parallax Basic Stamp to simulate the coding unit.