1. Why chose negative voltage?
2. Why chose 48V, not other voltage?
2006-09-12 20:53:24 · 6 answers · asked by sammyleung2001 1 in Science & Mathematics ➔ Engineering
Never heard the negative voltage bit. A nominal 50volts DC is what I believe BT still use. That doesn't prevent electric shocks, You can still get a tingle from it,( I was a BT technician) but it prevents fatal electric shocks.
p.s. "Ben" is mistaken, Bt/post office telephones was never 12v.
2006-09-12 21:15:59 · answer #1 · answered by Dick s 5 · 0⤊ 0⤋
The usage of 48V DC is to avoid electricution for the technicians. anything below that voltage will have a very bad voltage drop across the line and will not reach the consumer. Anything above that will definetely give a bad shock to the consumer.
I think the negative supply has something to do with the signal transmission on the same line along with the power.
2006-09-14 10:46:49 · answer #2 · answered by Vivian M 1 · 0⤊ 0⤋
maybe you have wrong information, supply voltage can't be negative.
they use 48 V to prevent the risk of electric shock
2006-09-13 04:00:58 · answer #3 · answered by albanese2003 2 · 0⤊ 0⤋
albanese2... is confused.
Supply voltage most certainly can be negative.
2006-09-13 18:55:28 · answer #4 · answered by dmb06851 7 · 0⤊ 0⤋
Well it must have changed since I was last twisting their wires together - it was 12v in those days.
2006-09-13 04:29:55 · answer #5 · answered by Dover Soles 6 · 0⤊ 1⤋
turn you meter leed over try agen
2006-09-13 04:17:27 · answer #6 · answered by me 1 · 0⤊ 0⤋