overhead wire frog at Lechmere

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overhead wire frog at Lechmere

Postby MBTA3247 » Sat Jun 20, 2015 8:33 pm

While going through some photos I took today at Lechmere, I noticed this peculiar-looking frog in the overhead above the switch where the two loop tracks split:

Image

Am I right in guessing that this is a 1970's-vintage frog set up for both pantographs and trolley poles?
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Re: overhead wire frog at Lechmere

Postby F-line to Dudley via Park » Sat Jun 20, 2015 9:06 pm

Possibly. They do truck the PCC's to Riverside for servicing, which means it would've behooved them to retain just a little bit of pole-worthy track in the yard to make sure they start up and move after a shop visit.
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Re: overhead wire frog at Lechmere

Postby Disney Guy » Sun Jun 21, 2015 7:26 am

Yes that is a frog assembly from the 1970's.

To remove the frog they also have to extend the wire that goes off to the right of the picture, extending it to the left of the picture and then tie it off to a line pole or something. No one has bothered to take the time and effort to do that to date. Also there is no compelling need to change it. It is not customary to simply attach the diverging wire to the straight through wire when no frog is needed or used.
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Re: overhead wire frog at Lechmere

Postby Gerry6309 » Sun Jun 21, 2015 11:17 pm

There is nothing peculiar about that frog. The two short pieces of wire on the sides prevent the pantograph from snagging on the frog. There were hundreds of them on the Green Line.

They are still used in San Francisco where poles and pans still interact. There is a special version which allows trackless trolley wire to cross single trolley wire for both poles and pans. No short circuits - No extended gaps.
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Re: overhead wire frog at Lechmere

Postby Disney Guy » Fri Jun 26, 2015 11:17 pm

In most cases on the T the frog casting in the middle (without pantograph compatibility) was the same one that had been there for years or decades and the side wires and perpendicular mounting brackets were added to it.

A 90 degree crossing can be tricky and almost always requires very slow speed operation of the pantograph car also. I have seen the special work in San Francisco but not an arrangement where trackless trolley wires had a side to side zig zag for the purpose of crossing the streetcar wire at an angle other than 90 degrees. Such a zig zag would not work for pole equipped streetcars.
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