HOW IT ALL WORKS - All Aboard: The Complete North American Train Travel Guide - page 167

should the engineer become unable to operate the locomotive for
any reason.
Head-End Power
Most of us take electricity for granted around the house and at
work. Flip a switch and the light goes on just about every time.
That's true on a train, too, but making sure it happens every time
is a bit more complicated. A fully-loaded passenger train requires
a lot of electric power. In the coaches and sleepers, electricity
powers the air conditioning, the lights, and the outlets for elec-
tric razors and hair dryers. It provides hot water for washing up
and showering. In the lounge car there are TVs, DVD players, a
microwave oven, and refrigerators—all are run by electricity. The
biggest user of electricity in the consist is, as you would expect,
the dining car with its ovens, ranges, grills, freezers, refrigerators,
dishwashers, and water heater. There's even a dumbwaiter in the
Superliner diners to carry food from the kitchen on the lower
level up to the hungry passengers on the upper level. It, too, is
run by electricity.
We've already talked about how diesel motors in the locomo-
tive run generators to produce the electricity that moves the train.
The electric power to run all those lights and appliances comes
from the same source: from a special generator used just for that
purpose in the locomotive. It's referred to as head-end power by
the crew; you'll frequently see it abbreviated simply as HEP.
Long before passengers arrive, the service crew is onboard
preparing the train for departure. They all need to see what
they're doing, of course. In particular, the dining-car crews need
to have all of their appliances working to store perishable food
and to start preparing food. Before the locomotive is attached to
the train, that electricity comes from a cable provided at the sta-
tion. It's called hotel power.