No. I was asking about the outlet receptacle type of GFCI.
But adding a single ground fault breaker per circuit to the panel would
seem to be a much better solution than adding multiple outlet type ground fault
Breakers are the best, however they generally cost 4 to 8 times as much, and
have the inconvenience of needing to go to the panel every time they trip
(and they can trip often when using power outside). The GFI plugs also have
terminals to wire additional plugs, lights, etc to protect things later on
in the circuit.
Because GFI breakers are at the panel, and all wiring, outlets, accessories,
etc are protected, not just the ones after the GFI outlet. GFI breakers
should be more reliable, especially since they are in a usually fairly
controlled environment. GFI breakers are also located in one spot - if a GFI
plug trips from an outlet later on in the circuit, then there may be some
difficulty in locating which GFI outlet tripped, or if a normal breaker
tripped from over current.
Ok, I see. It's not that the breaker is better, per se, it
is the position it occupies in the circuit.
Ok - that's a technical reason for breakers over receptacles
but only if it is true. Are GFCI breakers known to be more
reliable then GFCI receptacles, to your knowledge?
So that falls under "easier to use" (or whatever you
want to call it.)
Thanks! I don't necessarily agree that the points you
raised make a GFI breaker better than a GFCI receptacle,
but I can appreciate your rationale.
Rip one apart and see what failed. They usually have screws on the back. All
they are is a current transformer with both the hot and the neutral going
through it. If the current in the neutral and the hot is not exactly the
same, a current is produced in the current transformer. Most GFI's trip at a
5 mA differential, meaning a 5 or more mA current leakage from the neutral
or hot will trip the GFI. Perhaps the solder joints failed from the excess
That sounded too high, so I googled for confirmation. You're right.
When I worked in the hospital,
I remember the Electrical Safety Officer coming around with his cart
and checking every 110Vac gizmo. His spec was 15uA.
(You would marvel at this collection of cut-off molded 110V plugs.)
The 15ua spec is the limitation of leakage current to the patient, from
any piece of equipment. Not any sort of limitation for the GFCI device
itself. The spec at our hospital was 15 ua., but I think the spec was 10
ua in ICU & Surgery. The specs between the leakage current safety for
the patient and the amount of current necessary to trip a GFCI are
basically unrelated. The two were both safety factors but for two
different reasons. Even when an electrical device was grounded, there
could still be minute leakage currents, that could reach the patient.
These leakage currents had to be limited to below 10 or 15 microamps
because patients often had devices that made more intimate contact, with
the inside of the body. The skin does offer some resistance, however
even a range of microamps, could be fatal if connected internally.
I was a Biomedical Engineer/Safety engineer at a hospital for three
years. I had to test EVERY outlet and service almost every piece of
electrical/medical equipment in the hospital. The adjustable GFCI tester
I used was calibrated in ma and 99% on the GFCIs would trip as the knob
reached 3ma. They were click settings as opposed to a pot.
The first part of the input of the sensor for the GFCI was a toroid
transformer with three windings. The first two (I will call the main)
windings were wound as current opposing, around the toroid. Such that if
the two main windings(Hot & Neutral Lines) had the exact same amount of
current passing through them, they would cancel each other and no output
would be present at the third winding. The third winding was connected
to the differential inputs of an op-amp. If there was any imbalance of
current between the hot and neutral lines, the imbalance would negate the
cancellation and a current would be induced in the third winding of the
toroid, biasing the op-amp and in turn triggering the relay to break the
power circuit. The imbalance would be indicative of current taking an
inappropriate path to earth, through a path other than the neutral line
of that same outlet.
The statement that no safety ground line is required for the GFCI to
operate the way it was meant to, is true. However the test button would
not operate, because the test button put a resistor from the hot line, to
the safety ground line as a test, to cause the imbalance in the hot and
neutral lines. Even if no safety ground line was connected to the given
outlet, any amount of leakage above 2 or 3 ma, to another path to earth,
such as a waterpipe, would be measured, as an imbalance in the toroid
transformer, flip the output of the op-amp and in turn, trip the relay.
A safety ground is not necessary for a GFCI to operate normally, but of
course it would be stupid not to have a safety ground in any event.
(this post was read in alt.binaries.schematics.electronics)
The environment, and lack of testing, kills GFCI receptacles
installed outdoors. GFCI receptacles should be tested once
a month, per manufacturer's instructions. They have two
general categories of failure: electronic and mechanical.
Mechanical: the electronics operates a solenoid, which
operates the mechanical mechanism to open the contacts.
Heat/cold, humidity, dirt all can combine to gum up the
mechanical works - and that is particularly true outdoors
where there is more of all of those than indoors. When you
perform monthly testing, the mechanical mechanism is less
prone to freezing up due to the accumulation of gunk.
Electronic failure is also exacerbated by outdoor installation,
for the same three factors - heat/cold, humidity and dirt.
Heat harms electronics, temperature changes cause expansion/
contraction, humidity and dirt combine to form resistive
Note that I did not mention surges. I do not mean to
say that a surge could not be involved - I just want
to exclude that from the environmental factors I am
Install GFCI receptacles indoors to protect the outdoor
receptacles. It is a far better approach. The downside
is that a trip of the GFCI requires a walk inside to reset
Didn't you use the appropriate colored wires?
And as to why they didn't last you don't give us enough details.
There are different grades of receptacles. Plus being put outdoors
certainly does not help. I have no idea how good the housing is and
if it leaks. Plus I have no idea if the GFCI's that broke were cheap
ones made in China.
On 17 Nov 2003 12:22:31 -0800, scott email@example.com (Childfree
Should have also noted: The wiring in question was pre-placed for
expansion and capped off with wire nuts. So now I have to pair off
the black and red with the proper white, otherwise the GFCIs will trip
on any load.
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
Good idea if only using theoretical knowledge. Bad in
reality. It is a classical example of why decisions based only
upon theory are not sufficient. It is why they teach in high
school science the concepts. Required is both the theoretical
concepts AND experiment confirmation. Why is the refrigerator,
specifically demanded by code, not on a GFCI? Because GFCIs
are good in some places and not desirable in others - as has
been proven by experience. A blown GFCI on a refrigerator can
create food poisoning - something learned by field
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