GFCI Failures + Gadgets

"Jeff" wrote in news:2yZtb.26920$R13.818487@ursa- nb00s0.nbnet.nb.ca:

to

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.

buck

(this post was read in alt.binaries.schematics.electronics)

If you connect to the neutral (before the circuit) and to live (after), then that works.

Ian Stirling wrote in news:7h2ub.9408$ snipped-for-privacy@wards.force.net:

Does the use of a GFCI outlet help in a situation where is circuit is merely overloaded, but not short-circuited?

THX Wayne

It would be incpnvenient to wait for the Poco to reset it. The best thing would be a whole house GFCI, as is oftern used in most of the rest of the world.

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.

Two circuits, each common is white. Have to be paired correctly thru the GFCI.

Housing is standard metal outdoor/wet-location box.

Malaysia. The new ones are made in Mexico :-(

...Jim Thompson

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.

...Jim Thompson

So something minor happens, and all the lights go off? THIS IS A VERY STUPID IDEA. The code here requires separate lighting and receptacle circuits so the room doesn't go dark if you trip a breaker. Also, most areas of a home do not need GFCI protection. Wet areas, areas with bare concrete floors, or outdoors make sense. Some circuits it is illegal to use a GFCI breaker, like a refrigerator, or a freezer.

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.

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Really. If we have to ground-fault an entire house (because the occupants are too stupid and keep getting electrocuted to death) then maybe they should just go live in a hut somewhere in Afghanistan, where there is little risk of electrocution? ;)

In news: snipped-for-privacy@buckeye-express.com (Mark Jones):

Speaking of electrocution, I got quite a nasty zap from my plasma cutter the other day. 380VAC/20A plasma arc (open circuit), ground clamp wasn't getting sufficient contact with rusty metal. That was with rubber soled shoes (no steel toe), apron, and thick leather welding gloves. Anyone got a GFCI for that baby? ;)

Whole house GFI? Where is this "rest of the world"? GFI'ing a whole house would be stupid.

No, but I have a suggestion. A second ground clip, connected to a low voltage power supply, and a relay with a low voltage, high current coil. Then use the relay contacts to make sure that both clamps are making good contact, the plasma cutter doesn't fire up. The second clamp wouldn't have to be as heavy as the ground clamp, and you might even mount them together, so you put them on the metal like they were a single clamp.

scott posted, in part:

They might even have been some cheap crap made in the U.S.

A ground fault is not something i would consider minor. I'd rather be inconvinienced(sp?) by having to go to the box and reset the gfi than get shocked by faulty equipment. You can have a fault anywhere and on any electrical device on the house, why limit protection ?

We have that too. Different breakers for lighting and receptacles.

More info: country is Portugal, Here we have the meter, followed by a big breaker that is also a GFI (which we call "differential breaker") outside the house/apartment, the differential fault current is 500mA and overcurrent is settable from 10 to 30 Amps, according to hired power. Then, inside the house there is the main panel with a smaller breaker/gfi that feeds all the circuit breakers. Mine is 30mA, way too high, in my experience. Lights and receptacles have to be on different circuits. Power is 3 phase at least for most houses, i'm not sure about apartments.

Why?

I need one for my stick welder. I wont weld in the garage because I started a fire in there once (I was able to make it out). So, I weld outside, in front of the garage door. This is fine, except when the ground is damp. I have gotten zapped far too many times when changing the welding rods.

Why not just have one huge GFI for the entire electric grid. Then just hire a guy to sit there all day and reset it every 10 seconds. But, hey, look at the bright side of this. You would not need a flasher on your christmas lights...... :)

You don't need to shut down the whole house for one fault.

In the US we have individual GFCI breakers, or outlets, so you can protect any area without killing everything in the house. I prefer our method. Especially when I am working out in my shop after dark. I have trouble walking, and I would have to wait till daylight peeked into the air vents along the roof so i could see well enough to make my way out of a metal building with no windows.

Do you like to eat spoiled food? What happens if you are gone for a couple days and that GFI trips? with no one home to notice, you have a big mess to clean up, not to mention the cost of replacing all the food.