DANGER Third Rail!

Third rail on the Red Line

I have always been interested by electricity. My father is an electrician by trade and has always tried to teach me everything he knows. I have become very interested in the electrified third rail of the subway. Most subway systems in the world use an electrified third rail to power their trains. I wondered how it actually powered the train sets and if it was really as dangerous as people have made it out to be.

The MBTA does not use a protective covering
 like most Transit Systems 

First, I found out how it actually powered the cars. The third rail in the MBTA system is a steel conductor rail that provides 600v D.C. power to the subway cars on the Orange, Red, and Blue lines. The electricity that is constantly flowing through this steel rail is then picked up by the trains as they drive past. Each train in the system is equipped with two steel shoes that jut out from each set of wheels. The shoes glide along the top of the rail and collect electricity as the train rolls forward. Other transit authorities in the U.S have converted their third rail systems to allow for pick up by having the shoe glide underneath which would allow for covering of the top of the rail which could prevent electrocution.

Now onto the actual danger of the third rail! The third rail is advertised to passengers as an extremely dangerous thing. They basically say if you touch it you will be electrocuted. This is not entirely true though.  In order for electricity to flow through your body you must first be grounded. This means that one of your limbs needs to be touching the electrical conductor while the other is touching a neutral object or the ground in order for the electricity to flow.

Let's take a hypothetical situation here and say a person has just fell onto the tracks at Park Street. They are wearing rubber soled shoes, which act as an insulator, and are about to use the third rail to boost them self up to the platform. They proceed to jump and make it so both feet are on the third rail at the same time. They proceed to the platform unharmed. Now, if the person were to put one foot on the third rail and one on the ground below they would have been electrocuted. This is also why pigeons, rats, and other small animals can run freely along these tracks without harm.

So contrary to what you may have believed, touching the third rail does not result in an automatic death sentence. With that being said, the third rail is something NO ONE should mess around with. High voltage electricity of any kind can be very lethal.

Third rail demonstration image courtesy of HowStuffWorks.