The ABC's of GRS Model 5 Switch Machines

Today in North America railroads pretty much have two choices with it comes to power operated switch machines.  They can get a Union Switch and Signal M3 derivative or a General Railway Signal Model 5 derivative.  These aren't new models either as both designs have been around since the 1930's with only minor modifications.  For the M3 family there are a few basic sub-types, dual control, low profile, that rare one that can run a movable point diamond, but unless you find yourself face-to-face with an M2, the US&S offerings are pretty uniform.

The GRS Model 5 on the other hand, comes in 8 distinct offerings labeled A through G.  The first four, A, B, C and D, were available upon introduction of the family and they were eventually superseded by sub-models E, F, G and H, which are still available today.  Today I am going to take you through the identifying characteristics of each model, but first some quick notes on the common design elements.  All Model 5 switch machines consist of three sections.  A motor sticking out of one end in a conformal casing, a drive and locking section that moves the points and locks them in place, and finally a point detection section that houses contacts and other control elements.  Power only models have a flat top with a port for an emergency winding crank.  Dual control models have a hump on the top with the manual throw lever on one side.

Replacement GRS Model 5A point machine at JOHN ST interlocking in Toronto.

The Models 5A and 5B were required to be operated from a GRS pistol grip style of interlocking machine as those have motor control functions built in.  Power for the switch motor would be wired through the lever itself and upon the completion of throw the 5A or 5B machines would send a reverse current back to the tower that would allow the lever to be fully thrown in a process termed "dynamic indication".  During the throw the operator would actually need to monitor an amp meter in case the points became stuck and the motor started to overload.

The 5A's and 5B's are easily identified by their motor housing which features an angled access door.  The only difference between and A and B is that the B's are equipped for both manual and power control.

Surviving GRS 5C at CP-LAUREL

 The models 5C and 5D are intended to be operated from an all-relay or other non-pistol grip style interlocking system, although they could still be attached to the latter.  Unlike the 5A and 5B, these incorporate a motor controller into unit resulting in longer overall dimensions. 

Surviving GRS 5C at CP-TITUS

The distinctive feature of the 5C is a large box on the end of the motor which houses a brake to slow the motor as it reaches the end of travel.  The 5D is shown in the catalogue to have the same housing as the 5A/B, but I cannot confirm that layout from observations in the wild.

Uncommon GRS Model 5F at CPO-5 on the former D&H Colonie Sub.

 The Models 5E and 5F are the conceptual replacements for the 5A and 5B in that these also lack an internal motor controller, but there is no requirement to have a manually operated interlocking machine.  As some sort of motor control is still necessary, a 5E or 5F simply requires the control elements to be external switch machine itself.

GRS Model 5E conveniently installed as switch 5E on a SEPTA Market Frankford Line interlocking. 

The 5E/F are distinguishable by their noticeably reduced length compared to the internal controller models and with the other models the 5E is power operation only and the 5F is dual control.



5F model machines seem to be popular in New England, especially on the former Guilford Rail System, and also at some former B&O interlockings that had manned towers up through the 80's or 90's.

GRS 5G at CP-TITUS

 The 5G is pretty much an updated 5C without the large box for the motor brake on the end.  

The built in motor controller can be seen where the cover bulges between the point detector and the drive mechanism.

GRS 5H at CP-BURN

Of course the king of the GRS model line is the 5H, which is a dual control 5G.  Basically unless you want to buy a US&S style machine or you have a passenger or mass transit line that doesn't need dual control, you are going to be buying a GRS (now Alstom) Model 5H point machine.   Still, while these things are about as common and appealing as Darth Vader signals, if you keep your eyes peeled, you might just spot something a bit more unique ;-)