[BC] Google, today Hertz

[Broadcast List USER]

>From: "Jerry Mathis" <thebeaver32 at gmail.com>
>
>>Oh? Do you still consider Positive to be Ground? :)  I seem to remember a phrase, something like, "Ground is ground the world around, except in the Navy". :)

>From: "Gary Glaenzer" <glaenzer at frontier.com>
>and railroad locomotives     72-volt floating electrical system

Floating, oddly, yes.  72 Volts, no way!

Imagine a 3000 HP traction engine.  What would the current be at 72  
Volts?  Well over 12,000 Amperes as a pulling it out of my ear guess.

Of course, there are AC and DC traction motors, and there are  
switchers (small traction engines), freight engines, and high speed  
trains, but as a guess, we are over 1,200 Volts, up to about 8,000  
Amperes at lower Voltages.

72 Volts may be used for some control circuits, but I don't know much  
about them, except that they are very old and not all that safe, just  
ask the Washington, DC Metro, which runs at only 750 VDC, which is low  
and is a third rail system, not a diesel-electric system.  Metro  
trains are very light compared to main line freight trains.  Some  
third rail systems run as hight as 1500 Volts, over which they are  
considered unsafe.  Overhead catenary/pantograph systems are  
considered safe at much higher Voltages.

Heck, even my old Prius runs 274 Volts DC, and it is much lighter than  
a train!

Even in cities, like NY, where they have trains that run on both a  
third rail or overhead catenary, AND diesel-electric combination  
traction engines, they tend to use the diesel engines where legal  
because the current available is much lower when provided by a third  
rail or catenary.

--chip