TELECOM POSITIVE GROUNDING

[idlewilde]

WHAT IS THE REASON THE TELECOM INDUSTRY USES NEGATIVE 48V, POSITIVE GROUND?

 

[busbar]

Search

http://mirror.lcs.mit.edu/telecom-archives/

for discsussion.

 

[peebee]

Cool site, busbar.

I was interested to see what it had to say on this. No luck with the search engine, but the FAQ page linked to off the home page had the answer.

 

[busbar]

peebee, although it has nothing to do directly with grounding, polarity in protective-relay trip circuits seems to have a slightly conflicting rationale.

From

http://www.pes-psrc.org/k/rlytrckt.zip…

In order to minimize the effect of corrosion, relay coils should be permanently connected to the negative bus in dc control schemes. If moisture is present and the coil is directly connected to the positive bus, electrolytic corrosion may occur, causing the coil to become open-circuited and preventing the relay from operating.

 

[peebee]

Interesting. This would seem to expain too why cars have a negative ground. Strange that the same phenomenon would dictate different grounding arrangements.

You've made my head hurt once again busbar.

 

[busbar]

peebee — if severe pain persists, combined shots of intramuscular Stadol and Toradol can be quite effective.