The NRE 3GS21C is a genset switcher locomotive built by National Railway Equipment. It is powered by three Cummins QSK19C engines with each one producing 700 horsepower and creating a total power output of 2,100 horsepower. At least 16 3GS21C genset locomotives have been produced to date at NREC's numerous shops.
The same principle applies to all gensets:
When there is a low axle loading detected then only one or two gensets will operate, if there is a highaxle loading then all three modues will operate.
PHL was the first customer for the 6-axle model, ordering two units built on SD45T-2 cores.
DGNO, when under Rail America, ordered three 3GS21C's built on SD24 cores.
CSX rosters one, #1600, built on an SD40 core.
NS roster one, built on an ex-SOU SD40.
BNSF roster 10 units, built using SD40 cores, some of the units retain the SD40's cab.
IHB also rosters four units built in 2012, these locomotives were buil tin SD20 cores.
It has been rumored that there is a fifth PHL unit on the way.