In article . com, "Sasha" wrote:
Could you explain to me why connecting ground and neutral wire
"anywhere else but the entry service could result in a potential
difference across the ground wires throughout the system in case of a
short -- a dangerous situation"?

The neutral wire carries current, in normal operation. The ground wire does
*not*.

Having these two connected anywhere except the service entrance panel results
in current being present on the ground wire as well as the neutral - which in
turn electrifies *every* metal fixture box, *every* metal appliance chassis,
*every* plumbing fixture, etc. throughout the house.


They are connected in main panel?

Yes, and at the main panel, they are *also* connected to a grounding electrode
to ensure that both are at true ground potential _at_the_panel_.

What
"dangerous situation" can it be if neutral and ground wires are
connected somewhere up in circuits?

See above.

Also I checked my service which is
three years old and was done by license electrician has only three
incoming wires - there are no separate ground and neutral wire, just
one thick white wire connected to neutral/ground terminal.

Three wires coming in from the power company, yes. There should also be a
fairly heavy gauge bare (or green insulated) wire connected to the
neutral/ground bus bar in the panel, that is connected at its other end to a
grounding rod sunk into the earth outside the house and very close to the
service entrance.


--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?