Why do the lights on trains go off and on?

by Kev
Southwest Chief
Metra Locomotive
A Metra train is waiting for passengers at Chicago Union Station.

Have you traveled by train and wonder why the train lights go on and off? The lights go off and then come back on, usually after a train arrives at a station or not long before it leaves.  There is nothing wrong with the train, and there is a very logical reason why this happens. Amtrak and regional trains all can do this from time to time.

Let’s find out what’s going on!

Brief technical information

Different types of locomotives

Not all locomotives are created equal; freight locomotives, built for power and torque, run at lower speeds, but do not have the equipment to power electricity for passenger cars. On the other hand, passenger locomotives are designed for speed but need to do something else, for they need to create and supply electrical power for passenger comfort and use.

Passenger locomotives use a generator to generate electricity, and this power source is called Head End Power or HEP.

I’ve got the power! 

HEP produces power as a generator, either driven off the main engine or a secondary driver. To save fuel, they will cut or not used HEP at some station stops. Instead, they will switch to “house power” by plugging the train into a power cable at the station. It is not feasible or even possible to “plugin” at every stop. Because it would be more work than it is worth, and not every station has house power.

Oh yeah, electric trains and locomotives

Electric trains do not have a HEP unit but have a converter to take the incoming power and drop it down to a useful voltage for passengers to use while aboard the train.

Why train lights go on and off

At the station

Amtrak's Hiawatha in Milwaukee, WI
Amtrak’s Hiawatha sitting at the Milwaukee Intermodal Station

While they are changing power sources, the lights will go off in the car, and the emergency lights should illuminate. Usually, this takes a few moments to unplug the train from the house power, start the generator, and plug it back into the HEP.

After completing that, the power will come on soon. Typically there is nothing wrong with the train. There is a battery backup to run things like the PA system but not the toilets or other accessories.

While you are traveling

Passenger cars transfer power from one to the next via cables, sometimes these cables come undone during travel, which could cause the loss of electricity. Once the train stops and the crew can reconnect the line and all will be well.

Occasionally necessary to turn off HEP for safety checks. The electricity will come back up after the completion of the tests.

South Shore Line
A South Shore Line train going through the middle of the street in Michigan City, IN

On other reasons- Electric trains and locomotives

There are two ways electric trains get their power, one way is with overhead wires, and the other is the third rail.

An example of the third rail is Chicago’s CTA Subway/Elevated Lines. Each car makes contact with the third rail to get power for that car. When a train change tracks or crosses another track, it may momentarily lose electrical power because the car lost the contract with that power rail. As soon as that car passes through that area, the power will come back on again.

Other electric trains use overhead wires; examples include the South Shore Line, Amtrak’s Northeast Corridor, and streetcars in San Fransico. Power loss on these trains can happen if the train losses contact with the overhead power. Other reasons include or if they go into a dead block, as in for whatever reason the overhead line does not have electricity.

In a nutshell, that is what is going on!

Safe travels!
Kev

But wait, there’s more!

Looking for more information on traveling on by rail, check out my directory page of Amtrak travel. If you have questions, want to check the Travels with Kev social media, join the newsletter, or want to get ahold of me, visit this page.

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