You will note the confusion people in this newsgroup have about GFCIs.
And this confusion is not limited to those people. Experienced
electricians often don't even know what's inside of a GFCI. And
everyday-people, people who typically use receptacles, sometimes are
completely bewildered by them and how they should be used.
When ordinary Smo discovers a downstream receptacle to be dead,
sometimes that's the end of the troubleshooting. Smo simply concludes
there is something wrong with the electricity, and he or she leaves it
to somebody else to make the repair.
However, if the receptacle Smo is using has a reset button on it, Smo,
seeing the button right there, may try it, and he or she may succeed in
repairing the electric problem.
So a multiple-GFCI installation has a troubleshooting advantage. This
equates to an installation that is up and working a higher proportion
of its life. Thus, the multiple installation is superior. However, it
In new construction, the labor cost of installing a GFCI receptacle is
equivalent to that for a regular receptacle. The cost difference in
materials isn't substantial. Consequently, new construction (on all but
the cheapest of projects) should have a GFCI at every receptacle where
GFCI protection is needed.
In retrofits, each replaced receptacle is an added cost. And in some
older houses, the old small boxes won't accommodate a GFCI. So an
inexpensive way to protect all the outlets on a circuit is to just use
the GFCI on the first outlet.
It seems I've learned something today. It sounds like you're describing
an outlet and circuit breaker in one box.
So, when any outlet on the "output side" trips it, the whole string
goes out? Does the first one still work? I.e., does it have two reset
The GFCI and duplex receptacle are combined in a discrete or single
device. Inside of this device is the GFCI circuitry. The connecting
slots for a plug and the downstream (labeled "load") connectors are
_both_ downstream from the circuitry.
If the GFCI is tripped, everything goes off.
There *are* two buttons, but one is "test" and the other is "reset".
One of the 'recent' innovations is to build the GFCI circuit breaker
into the 'first' outlet in the chain. On that outlet, the two sets of
connections are isolated from each other, so that all downstream outlets
are then protected. This allows you test and reset the circuit from
inside, without having to go find the breakerbox. It has become
standard in the NEC to do it that way now.
But, the only way to really tell which outlet is first is to pull each
one out, and buzz out each side. Takes a while, but is the only sure
way to find out. Unless, of course, you took pictures of the wiring
before they put up the sheetrock!
Well, if you had a fast scope, and a pulse generator, and pulled the
end out of the breaker box and drove it like an RF transmission line,
you might learn something by plugging a simple "nightlight" load into
each outlet while watching the scope.
If it's on the first floor and the basement is unfinished, you might be
able to get a good idea just by looking up.
Time Domain Reflectometry measurements (sometimes called Time Domain
Spectroscopy techniques) work by injecting a short duration fast rise
time pulse into the cable under test. The effect on the cable is
measured with an oscilloscope. The injected pulse radiates down the
cable and at the point where the cable ends some portion of the signal
pulse is reflected back to the injection point. The amount of the
reflected energy is a function of the condition at the end of the
cable. If the cable is in an open condition the energy pulse reflected
back is a significant portion of the injected signal in the same
polarity as the injected pulse. If the end of the cable is shorted to
ground or to the return cable, the energy reflected is in the opposite
polarity to the injected signal. If the end of the cable is terminated
into a resistor with a value matching the characteristic impedance of
the cable, all of the injected energy will be absorbed by the
terminating resistor and no reflection will be generated. Should the
cable be terminated by some value different from the characteristic
impedance of the cable the amount of energy reflected back to the
cable start point would be the portion of the pulse not absorbed by
the termination. Also any change in the cable impedance due to a
connection, major kink or other problem will generate a reflection in
addition to the reflection from the end of the cable. By timing the
delay between the original pulse and the reflection it is possible to
discern the point on the cable length where an anomaly exists. The
cable type governs this signal propagation speed. For example normal
Category 5 cable propagation speed is 66% the speed of light, and for
most coaxial cables this value is between 66% and 86%.
One circuit example for TDR signal generator:
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
you can get outlets that proviide proteted output terminamls
on the back to connect protect to other downstream standard outlets
. Mains Hot ------+ +----------+-------------+
. Mains Neut. ----|-+ | +--------|--+----------|--+
. | | | | | | | |
. ------ Ordinary Ordinary
. | GFCI | Outlet Outlet
note: ground connection present but not shown
In Canada, GFCI outlets have input and output terminals so you can
protect a whole chain of downstream outlets with just one GFCI. You
could put a GFCI on every outlet, but that's overkill. Or should I say
Right - when wired as drawn above. But GFCI receptacles
can be wired to protect downstream receptacles/wiring as
well. They are marked with a line and load side. The
wiring on the line side of the GFCI receptacle is not
protected by the GFCI. The GFCI contained receptacle,
and everything on the load side is:
Mains Hot -------| GFCI |------| Regular|--- etc
Mains Neut. -----| Recpt. |------| Recpt. |---
Cheaper to install a GFCI receptacle in the first position
on the branch, and equally effective for ground fault
protection as a GFI circuit breaker. But you can't do
that on a multiwired branch with a shared neutral. For
such a branch circuit, you wire only to the line side,
and the GFCI receptacle feeds nothing down stream. Or
you could feed a non-shared neutral circuit downstream
through the GFCI receptacle, which implies adding
an extension to the existing multiwire.
On Sun, 12 Feb 2006 09:43:39 GMT, "Nehmo Sergheyev"
If you go to RatShack and buy one of their little amplified speaker
boxes (looks like an old transistor radio) and a telephone pickup
coil, that combo can ge used to hear 60 Hz magnetic fields near wires.
So connect some load gadget to the various outlets one at a time.
Something that has nasty current harmonics, like a PC or a tv set, is
best... makes the current distinct and more audible. Now you can trace
the wires in the walls and figure where the current is going. You may
wish to kill other breakers in the house, or have somebody cycle your
test load, if things get confusing.
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