Re: Phone Line Interfacing - FCC Part-68


w_tom wrote:

On May 22, 11:19 pm, rickman <gnu...@xxxxxxxxx> wrote:
If your equipment does not have an electrical connection to anything
else, then you don't need the fancy earth ground and transorbs. The
transorbs aren't really safety related, IIRC. There are two things
you need to protectphoneline equipment from, lightning caused surges
(not necessarily a direct strike) and AC mains crosses. The lightning
stuff is more of an equipment issue. There is not much of anything
that you can do which will protect in the event of a direct strike to
thephoneline. It will roll in on the wire and fry every thing
connected, protection or no. But a close by strike will create a
voltage/currentsurgein the line which can be protected against
depending on the strength.

So a telephone Central Office computer; connected to overhead wires
all over town;


Were do they still use that much areial cable? Around here most telco
plant is underground, and fiber optic.


that surges maybe 100 surges during every
thunderstorm. That computer must be replaced after every
thunderstorm? Of course not. Due to a properly earth surge protector
where wires enter the building, then direct lightning strikes cause no
damage.

Telcos install an earthed protector to protect their equipment.
Telco's protector on your end may do same for your equipment. But only
as effectively as an earth ground that you have provided. Surges that
do not enter a building need not cause damage. Common mode choke is
easily compromised if a surge has no other path to earth. Common mode
choke as secondary protection works if surges are diverted to earth
via the 'whole house' protector. Surge needs a path to earth.


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