Grade Crossings

When looking at a grade crossing, no 3rd rail appears to be present. If this is the case, then how does each car keep electrical power over the grade crossing? Thanks...

If the crossing's short enough, the shoe on the rear truck keeps contact, the shoe on the front drop off, then picks up, then the rear comes off, and picks up again. Thus, there's always a shoe on the rail. I think married pairs will share power between each other still. There's no trainlined power bus like the MP-54s had (yes, they did at one time).

If the train's going fast enough, it doesn't matter, unless the first car's batteries are low, in which case the brakes can dump. I've been on amazingly dead cars that didn't, though. One time during the 'summer of hell' the other year, the first car had no MA, no A/C, no lights, sluggish doors, yet still the train kept going. I think about the only thing the car WAS doing right was taking power - you could hear the controller klunking away under the car...

If the crossing's long enough, yes, the car loses power over the crossing. Jamacia's known for this, esp if the train stops and the MA set winds down - everyone gets to sit in the dark until the car hits the third rail again and the MA spins up and all.

RC '75,

Phil explained it pretty good.
If I may try to clarify just a tad:

Third rail 750VDC buss line power is contiguous to a married pair of cars on all present LIRR EMU equipment ("M" series cars). If any one of the 8 contact shoes on the married pair of cars is on third rail, both cars of the married pair have 750VDC available for their high voltage loads. (Incidentally, all 8 contact shoes are also at 750VDC potential if any one shoe is touching third rail...don't touch them! Yes, even the ones on the other side of the train that are not on third rail! )

When all shoes in a pair are off third rail, the battery set in the pair of cars normally keeps all your low voltage circuits powered, awaiting return of third rail power.

If the pair of cars has weak battery set, the other pairs of cars in the train are supposed to provide some help to the pair in the gap with weak battery. Their rectifier voltage (if their M/As are running) or their battery sets push voltage through battery trainline contacts in the electric couplers.
The battery trainline feature doesn't always work as hoped, however. And sometimes trains "dump" (go into emergency brake application because brake pipe vents) and/or have some other electrical problem.

Tom