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 Post subject: Re: Streetcar conduit systems
PostPosted: Thu Jul 25, 2013 7:11 pm 

Joined: Sun Aug 22, 2004 7:25 pm
Posts: 1881
From 100 Years of Capital Traction:
Quote:
In 1949, Mr. Harry Blunt, Chief Engineer, Capital Transit Co. estimated costs at $36 a running foot for overhead wire versus $100 for conduit construction.

Since both sides of the current distribution system in a conduit system were insulated from ground, it had an advantage not possible with overhead trolley systems. The conduit was sectionalized and, if a leakage to ground occurred in one section, it could be temporarily corrected simply by changing polarity in that section by means of double-pole, double-throw switches at the substation.

Model railroaders may wonder why a reversal of polarity didn't reverse the car. Unlike permanent magnet motors, field wound motors can be reversed by changing polarity of the field or the armature, but a change of polarity of both has no effect. Thus a change at the source of current would have no effect.

To enable motormen to know when to cut power at conduit breaks and how to position the car at the plow pits, it was necessary for him to know which truck the plow was attached to. Thus, double end cars had painted on the controller - or prominently on the front platform area - "1 Plow" or "2" or a variation "No. 1 End" or "No. 2 End." In each case the numeral "1" meant the plow was on the truck nearest the motorman while the numeral "2" meant it was on the far end of the car.


Wesley


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