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Default house wired without separate ground - problem?


wrote in message
oups.com...

Bob F wrote:
"Nate Nagel" wrote in message
...
All right, I'm feeling mildly dumb and a little sheepish not to

mention
slightly sick here... just bought a house for the first time less

than
a month ago, and knew that it had some minor wiring "issues" but now
that I'm assessing what I have it appears that there are bigger issues
than previously anticipated. Anyway, here's the deal. House is a two
story colonial with full basement, built late 1940's.
It appears that throughout the house wherever the wiring was
hidden behind plaster it was run in NM not BX and there is no

grounding,
period.


It's also possible that the wiring could be knob-and-tube in a house of
that age.

Bob


Knob and tube went out before the 1940's in almost all parts of the
United States which is where the OP is from, I think.


My first house, built in 1948, had knob and tube.

Bob


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Default house wired without separate ground - problem?

(Doug Miller) writes:

In article , Nate Nagel wrote:
Doug Miller wrote:
In article , Nate Nagel

wrote:


but the receptacles installed on the first and second floor are
grounding type and it appears that the ground is provided by a jumper at
each receptacle between the ground terminal and the neutral. I realize
that *theoretically* this is functionally identical,


No, it isn't, not even theoretically. This makes it possible for the chassis
of any piece of equipment plugged into the outlet to become electrically

live,
and it's not at all safe.


It is functionally identical, so long as the neutral isn't broken.


No, it is *not*, as I just pointed out. You seem to be unaware that the
neutral wire carries current.


That's true.

If the ground and neutral are interconnected at
the receptacle, anyone simultaneously touching the metal chassis of any
equipment plugged into that outlet, and anything else that's grounded (e.g. a
water pipe or faucet, or simply standing on a concrete floor) makes a parallel
path to ground for the current in the neutral conductor -- and enough current
can pass through that person's body to cause a significant danger.


In normal cases there are not enough current that can pass
through the person body to cause a significant danger.

Even though the is a lot of current going on the neutral
wire, the potential difference between the neutral wire and
the "real" ground is quite low. Typically in normal operation
(all wiring OK) up to few volts, transients to higher voltages.

When the voltage difference between ground and the neutral
is just few volts, not much current can flow between a person
that touches them both. The human body and skin has
considerable resistance, especially on low voltages.

The dangerous voltage differences exist and dangerous currents
can only flow when the neutral gets broken...

Wiring where grounded outlets gets only two wires
(live and combinet neutral+ground) used to be quite common
practice in several European countries (for example Finland)
for a quit long time. At some point the regulations changed
demanding separate neutral and ground wires to outlets in
most cases.

--
Tomi Engdahl (
http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/
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