Posted by Mr. Bill on January 10, 2008, 10:05 am, in reply to "Re: -48 volts"
Great Answer, Ashley. You know your stuff.
Also, it is defined as "nominal -48," which means that the actual voltage will be 'about' 48. When it leaves the battery, it as actually -52 to -53.5vDC. A few volts are lost to resistance here and there. I remember the old power control boards, with the voltage "floating" in this range.
I remember too an crossbar course I took, back in '70 or '71 that the instructor told us that (-) negative battery is used, with (+)positive serving as return, or ground; because positive ground resulted in less electrolosys damage to metal cable sheaths in the field.
--Previous Message--
: The term -48 refers to the fact that the
: operating voltage for the exchange equipment
: is negative 48V with respect to the ground -
: the positve pole of the 48V supply is
: grounded.
:
: Similarly in the days of vacuumtube carrier
: systems there were two other voltages used,
: these being -24V for the filament supply
: which was positive grounded as for the
: switching equipment, and +130V for the plate
: supply of the vacuumtubes which was negative
: grounded.
:
: Note also that -48V is used to distinguish
: from the +48V supply used in Strowger type
: exchanges that is used as a meter battery
: source. This supply is also negative
: grounded.
:
: Additionally, there is also the +48V supply
: used in doublecurrent telegraph working
: where a Mark is -48V and a Space is +48V.
: This source is also negative grounded.
:
: And furthermore there is also the +48V
: supply used on very long two and fourwire
: physical trunks so that the effective
: operating voltage of the circuit becomes 96V
: instead of 48V; -48V is applied to one wire
: while +48V is applied to the other wire.
:
: --Previous Message--
: An instructor at a class posed the question,
: Why do phone companies use the term -48?
: Were did it originate? Were did it start? He
: says he is not actually referring to the -48
: power used in the central office but
: something else. I don't know? Can some one
: help?
:
:
:
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