.
I thought GFI's operation had nothing to do with the ground. It trips when it detects a current imbalance between the hot and neutral, regardless if theres a ground or not. I could be wrong though.
According to Nehmo :
I think that most people would find that GFCI's don't false trip very often. If at all. I've never had one of mine trip when it wasn't clear it _probably_ had a good reason. False trips are suggestive of electrical boxes getting damp, bad extension cords, or oddities in old wiring (intermittent neutral-ground shorts) etc.
By putting in more GFCIs, you're increasing your probabilities of GFCI failure _and_ false tripping.
I'll bet that if you did a good sized survey, you'll find _more_ trouble (including out-and-out GFCI failure) if you put an GFCI in every receptacle box than you would with a judiciously placed single GFCI outlet (or breaker).
Well, as long as I have your attention, it makes absolutely no difference whatsoever which outlet on a main line has a GFCI - each one only protects itself and what's plugged into it, and couldn't care less what's happening downstream:
[view in fixed font, with wrap off] . . Mains Hot -------+-------------+-------------+ . Mains Neut. -----|--+----------|--+----------|--+ . | | | | | | . ------ ------ ------ . | GFCI | | GFCI | | GFCI | . ------ ------ ------ . P.C P.C P.CWhere "P.C" means "Protected Circuit".
What has been suggested, (sorry, don't remember by whom - jalegris?) is to use a GFCI circuit breaker, which goes on the left: . . ------- . Mains Hot --| GFCI |----+-------------+-------------+ . Mains Neut.--| C.B. |----|--+----------|--+----------|--+ . ------- | | | | | | . Ordinary Ordinary Ordinary . Outlet Outlet Outlet
That's "on the left" in my attempt at a diagram - in real life, it goes in the breaker panel.
Or, of course, you could upgrade your wiring - it will increase the resale value of the house considerably! :-)
Good Luck! Rich
Rich,
That's not exactly true. The GFCI receptacles have a LINE input and and LOAD output. Any receptacles connected to the LOAD output terminals of the GFCI are also protected circuits.
Not true. GFCI outlets have a gazinta and a gazouta. Anything attached to the gazouta side is also protected by the GFCI. The feed-through is usually rated at 20A, which is likely the same as the branch circuit. If he can find the first outlet he can protect the whole circuit with a $10 GFCI outlet, rather than a $25 GFCI breaker. He won't have to go into the basement (or outside, in my case) to reset the GFCI either.
It could be a GFCI in the first outlet on the circuit, as well.
Maybe.
In Canada, at least, it CAN make a difference depending on where you put the GFCI outlet - it has input and output terminals. By connecting it as the first in a chain you can protect all the other downstream outlets. That's what the OP is trying to do. Of course, you could put GFCI's on every outlet, but it's overkill. Or should I say underkill?
-- Joe Legris
Hi Rich, 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!
Charlie
Chris Lewis -
Nehmo - GFCI nuisance trips are common. This article, Think Like a GFCI
Chris Lewis -
Nehmo - No. Cumulative leaks on downstream outlets would be eliminated because there would be no downstream outlets. And as I said before, any tripping incident is localized, allowing for easy troubleshooting, which is even more easy if the GFCI receptacles have indicator lights.
I repeat: the ideal arrangement is a GFCI at every receptacle that needs protection.
Mine are like that. In most cases, wires to each receptacle and switch come from a junction box at the ceiling light fixture. The whole thing would look something like a giant octopus on top of the room with tentacles hanging down all over. In that case, maybe you could put a GFCI in a box next to the existing ceiling one. The other rooms use pigtails so each receptacle has it's own connection (no others depend on it).
My attic looks like that.
Something that won't work on shared neutral circuits.
Ground each hot connection, through a resistor (just like the test buttons do). The resistor limits current in case the GFCI doesn't work.
A GFCI doesn't use ground. It responds to unintended ground connections (indicated by a difference brethren hot and neutral currents), like when you touch a defective power tool and become part of the circuit.
The problem with connecting grounds (when no connection to earth exists) is not specific to GFCIs. If you have 2 receptacles connected this way, and an appliance plugged into one has a short from hot to ground (one that's not quite enough to trip the breaker), the ground connection at the other receptacle is now hot. You can get electrocuted by touching what was supposed to be a safety ground.
That's when they're ALL first receptacles. Seems to be a common situation here.
And write down your test results, to avoid forgetting and redundant retesting. You could also mention what to do if you see only one pair of wires to the receptacle, maybe even short wires going to a soldered junction.
I suppose you have fewer than 7 2/3 receptacles :-)
According to Nehmo :
There are many ways that nuisance trips can occur, but they are by no means _commonly_ occuring.
The article deosn't say anything about how common these actually occur, and you're misinterpreting how "harmless" some of these things are.
There's no such thing as a harmless leak. Even a neutral-ground intermittent is potentially a serious problem if it causes the grounding circuit to corrode. It's not supposed to carry current _unless_ there's a fault. Continuous current, especially in the presence of moisture, can easily cause grounding connections to eventually fail. So that tiny little leak can cause a full grounding failure later on that kills you.
The GFCI is trying to tell you something.
If you follow the guidelines of where to use GFCIs, nuisance trips are virtually non-existant. I've never seen one. And I've installed quite a few.
Cumulative leaks is not likely to be an issue. Leakage in properly installed and dry systems is _extremely_ low. Vastly lower than the milliamps needed to trigger a GFCI. Not enough, even when multiplied by 10 or 15 to be an issue. And if it was, you still have issues with ground circuit corrosion.
The other point I was trying to make is that by multiplying the GFCIs by a factor of 10, you're multiplying the possibility of GFCI burnout (by line-side spikes etc) by a factor of 10. Which in the long run outweighs the issue of nuisance trips.
From a reliability standpoint, it's better to have fewer than more of these things.
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 . ------ . P.C
note: ground connection present but not shown
jalegris
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 costs more.
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.
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 underkill?
-- Joe Legris
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. |--- --------- -------- Line Load
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.
Ed
Is that different from the LINE and LOAD terminals?
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