Of ice and electricity

Photo of what winter weather may look like, westbound at Hawthorn Farm

Steven Vance recently forwarded me a question about why CTA‘s rails have been sparking. Unlike MAX trains which get power from an overhead wire system, their trains get power through a third rail system. However, arcing in both kinds of power systems during winter weather is typically caused by ice. Ice building up on the wire (or third rail as the case may be) acts as an electrical insulator, preventing the carbon shoe from making contact with the wire where the ice accumulates. This interruption in the flow of the current from the wire to the pantograph is visible as arcing.

Here’s a video of a MAX train pulling into & out of a platform where there was some ice on the catenary, and you can easily see the effect that it has:

To help clear ice from the overhead wire & prevent it from accumulating, a few of the Type 1s (107-112) are equipped with ice cutters which are put into use for major freezing rain/ice events. I don’t have a picture of any of them in use (though I’m willing to accept donations!), but they look like a second pantograph and function by heating/scraping ice from the overhead wire. Unlike the pantographs, ice cutters only draw current to heat the elements and not to provide power to the train, so they won’t arc the same way the pantographs do in ice. Their function is strictly to clear ice from the wire.

Pantograph (left) raised, ice cutter (right) lowered

If you’d ever seen one of these cars and wondered why it has two pantographs, wonder no more! It doesn’t – one pantograph, one ice cutter.

View from above; the ice cutter is the one closer to the coupled end, the pantograph is the one in contact with the wire closer to the vantage point. Bonus cameo appearance by car 235