alt.engineering.electrical

"Usual Suspect" wrote in message
news: @ ...
>> We have railroad equipment with 12 and 24 volts direct current with
>> negative
>> ground. I have junior mechanics asking why a positive engine starter
>> post
>> is grounded to frame and it doesn't short out. I told him it was
>> protected
>> with diodes somewhere and acted as an arc suppressor, but I was just
>> guessing. Does anyone know for sure or have information/schematics or
>> something that explains this?
>
> You don't have negative ground system. If the positive terminal is
> connected
> to frame, it's positive ground.
>
> Same as negative ground system, just invert your thinking... :-)
>
> There may indeed be arc-suppression diodes in the circuit, but this has
> nothing to do with a positive ground system. Same diodes may exist on a
> negative ground system. They will protect switch contacts equally on both
> types.

If you remember to install them correctly :-)

Installing them backwards because you aren't aware it's a positive ground
system will let the 'magic smoke' out of them.

daestrom