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The HEP Units

By Daniel Garcia
Revised by James Bow

Passenger trains have special requirements that freight trains do not have: the need to heat passengers and give them light. For passenger coaches, the only source of this power is the engine at the front of the train. However, generating the heat and the electricity required to power the passenger cars drains energy from the locomotive’s tractive effort. Also, if the diesel engine were to fail, passengers would suddenly find themselves without light or heat.

To compensate for this, passenger trains often have separate Head End Power generators built to provide the electricity required. Sometimes these HEP generators are within the engine that’s pulling the train, but oftentimes, especially in the 1960s and the 1970s, a separate locomotive unit is cut into the train, with its engine used to provide power for the passenger cars.

GO Transit started life as a low-cost operation designed to provide service with as few start-up costs as possible. Their first locomotives were bought with an eye to either leasing or selling back the locomotives to freight railroads on weekends, or should service ever be cut. As a result, many of GO’s early locomotives did not come with HEP generators. To compensate, GO purchased separate locomotives and modified these to provide HEP. Two series of cars existed.

The APUs

Whereas a locomotive needs a control cab to drive it, the only thing required from an HEP unit is an engine to power a generator. In the late 1970s, GO Transit bought three used F7B locomotives from Northern Pacific to provide HEP on its trains. These old diesel locomotives had been built between 1950 and 1951 as cables locomotives to provide additional power to F7A units (with cabs) in front of them. The cars were rebuilt by Crome Crankshaft, replacing their engine, main generator and traction motors. They could not be used for propulsion anymore; that was the job of the lead locomotive.

GO Transit called these three units, numbered 800-802, “Auxiliary Power Units” (APUs). They used a General Motors 600kW 16V149-powered HEP generator, able to provide full electrical power for a 12-car train. They were frequently paired up with the GP40-2L series (700-710) and the GP40M-2 series (720-726) locomotives, and on occasion with the GP40TC’s (500-507) and the F40PHs (510-515). The F40PHs had an HEP engine, but it left the main locomotive underpowered, so the APUs provided an additional kick. The cars were also used whenever GO leased their non-HEP equipment to other railroads, including VIA Rail in 1984 to deal with an equipment shortage, or to Los Angeles, California, in the wake of the 1989 Loma Prieta earthquake.

Once the F59PHs retired most of the non-HEP locomotives, there was no need for these ACUs to remain. Car 801 was sold to Ontario Northland in 1994, while the remaining two were scrapped in 1995.


As the APUs were cab-less and often found behind the more prominent locomotives on a train, it was easy to overlook these vehicles. The same could not be said for the other HEP units. Here, GO purchased eleven F7As — streamlined locomotives built between 1950 and 1953. The cars underwent a similar rebuild as the APUs, losing their traction motors and main engine in place of a 900 hp HEP generator, but the cabs and their controls were retained to be used in push-pull operations, in lieu of a cab coach. These cars were called Auxiliary Power/Control Units.

The first four APCUs were obtained from Ontario Northland in 1974. After the rebuild, they arrived on GO property numbered 9858-9861. They were renumbered 900-903 two years later. The second order brought another five APCUs from Ontario Northland, numbered 904-908, when they arrived in 1976.The final two APCUs arrived in 1981, purchased from the Chicago, Milwaukee, St. Paul & Pacific railroad sfter the company went into receivership. These were numbered 910-911

Just as with the APUs, the fate of the APCUs was sealed when GO’s non HEP locomotives were retired and replaced by the F59PH series. They were declared surplus and scrapped in 1995, save for #910, which was sold to TriRail, along with GP40-L2 locomotive #703.

HEP Units Image Archive