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0v-(-)48v=48v-0v?

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Wond3rboy

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Hi i have a simple question.The voltages above are equal by magntude right? Then why do they use -48v in a PSTN. Why not 48v?
 
What, the telephone line? They don't, so far as I know. Wouldn't surprise me if they did, or just flipped a coin to see if they would reference it positive or negative - remember, these are the same people who invented the decibel.
 
I know that telephone exchanges use a positive earth.

I don't know why, perhaps it's because n-type devices can switch the high side but I doubt it because it was invented before semiconductors.
 
I know that telephone exchanges use a positive earth.

I don't know why, perhaps it's because n-type devices can switch the high side but I doubt it because it was invented before semiconductors.

If positive is used and negative is grounded, all the external copper wire used even now would get eaten off due to electrolytic action of atmosphere, grond at -ve and wire at positive.
This aspect was elaborated in Telephony by Atkinsin and also in articles of Lekurt demodulator. Lenkurt is a company of US in telecom those days.

now with positive grounded, maximum, it would add some coating on the wires but never remove the metal
 
If positive is used and negative is grounded, all the external copper wire used even now would get eaten off due to electrolytic action of atmosphere, grond at -ve and wire at positive.
This aspect was elaborated in Telephony by Atkinsin and also in articles of Lekurt demodulator. Lenkurt is a company of US in telecom those days.
Please post a referance. I find this very difficult to believe.

Some old cars had a positive earth and it caused a huge number of corrosion problems, now all cars are negative earth, it's less of a problem.

I would have thought that corrosion would be more of a problem in exchanges which are positive earth.

If I remember my electrochemistry correctly, in a battery, the anode is always the part which gets corroded.
 
Please post a referance. I find this very difficult to believe.

Some old cars had a positive earth and it caused a huge number of corrosion problems, now all cars are negative earth, it's less of a problem.

I would have thought that corrosion would be more of a problem in exchanges which are positive earth.

If I remember my electrochemistry correctly, in a battery, the anode is always the part which gets corroded.
Don't see IN the battery. See the case an electroplating set up using a battery. the metal transfer takes place from positive connected metal to the negative connected object.
this very thing happens in the telecom external plant that used consist of lots of external copper wires. the atmosphere between ground and the wire would behave like electrolyte. slowly the wire were eaten away by electrolytic process.

Being a telecom trained professional, I have seen this in text that I quoted. now that I am retired, and presently these books are not with me. producing a proof would not be problem. I have to go to my erstwhile departmenrt , take a scan and upload the relevant page.
Perhaps many may throw it off as trash, being scientific observations of 20th century.

just study what happens in the electrolysis tank and the same thing happens in atmosphere also.
 
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Oh no, not decibels again...
I know. But we just need to accept that duffy is rabid about the decibel and no amount of rational discussion will change his mind.:rolleyes:
 
Thanks,Sarma.You finally cracked it.

I did not crack, Perhaps as a new comer to electronics &communication, it may be appearing new to you. It is old as 6 decades.And it is recorded in many telecom related Text books.
 
Don't see IN the battery. See the case an electroplating set up using a battery. the metal transfer takes place from positive connected metal to the negative connected object.
this very thing happens in the telecom external plant that used consist of lots of external copper wires. the atmosphere between ground and the wire would behave like electrolyte. slowly the wire were eaten away by electrolytic process.
Yes you're right, I got it backwards.

But from what you're said, a positive earth would increase the corrosion. Everything connected to the positive side of the battery would get corroded more. This would mean all metal parts of the building and enclosures in the installation would be more prone to corrosion than if a negative earth system were used.
 
Yes you're right, I got it backwards.

But from what you're said, a positive earth would increase the corrosion. Everything connected to the positive side of the battery would get corroded more. This would mean all metal parts of the building and enclosures in the installation would be more prone to corrosion than if a negative earth system were used.

yes Hero999, my sentence formation was a bit confusing.

it should have been like this . May i call it poor sentence formation (-- i remember discussion-- regarding English language command and its benefits.)
If positive is used and negative is grounded, all the external plants' copper wire used even now would get eaten off due to electrolytic action of atmosphere, ground at -ve and wire at positive.
..............
now with positive grounded, at the maximum, it (ground ) would add some coating on the wires but never remove the metal


Sorry Hero999, for my bad English.
 
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Why is negative earth used for cars then?
 
Why is negative earth used for cars then?
it is to be analyzed. i did not delve in to the automobile subject. but there were some vehicles with positive ground also. but the over time the -ve ground be came more prevalent.

most of the wiring in any car is insulated wires as against open bare copper or iron wires used for serving telecom external plant.
 
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