Two phases to house - loss of neutral
in [Repair]
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From: D Yuniskis on 28 Nov 2009 13:16 PeterD wrote: > On Fri, 27 Nov 2009 17:40:49 -0700, D Yuniskis > <not.going.to.be(a)seen.com> wrote: > >> PeterD wrote: >>> On Mon, 23 Nov 2009 18:38:47 -0700, D Yuniskis >>> <not.going.to.be(a)seen.com> wrote: >>> >>> >>>> This is how GFCI breakers work -- they watch for current "leaking" >>>> off to ground someplace other than in the "return" conductor. >>> No they don't. They look for imbalanced current flow between the two >>> conductors. >> Gee, isn't that what I *said*? > > No, you didn't. > >> How do you get an imbalance if >> current isn't *leaking* off to ground someplace other than >> in the "return" conductor? > > Re-read your post. I don't have to re-read it -- I *wrote* it! A GFCI is nothing more than a tiny transformer with "sense electronics" as its "load". The primary to the transformer is the circuit being monitored. *BOTH* conductors pass through the transformer. Since an alternating current generates a magnetic field, that field couples *through* the transformer to the *secondary* of the transformer -- which is the "sense electronics". The field generated by the primary is a function of the *net* current flowing through the primary "winding" (winding can often be confusing in this context as it is usually just a "single turn" -- as such, it doesn't even go completely *around* the transformer's core!). All of the current flowing *to* the INTENDED load (remember, the GFCI can also see an *unintended* load!) goes through the supply/hot lead, through the transformer's primary. All of the current *returning* from the load passes through the neutral/return conductor *also* through the transformer's primary. If any of the supply current has "leaked" away via some other path (to "ground") -- like through a person's body -- then the current to and current from will not be equal. As such, the magnetic fields generated by each conductor won't *perfectly* cancel out. As a result, some energy will be coupled across the transformer's core to its secondary. You can have a *lot* of gain across the transformer since the secondary doesn't need much power to function. As such, you can look for very small "leaks" even in circuits carrying very *large* currents! I.e., aside from the physical size of the transformer and the primary conductors passing through it, a GFCI for a 1000A circuit is essentially the same as one for a 20A "household" circuit. (N.B. this would not be the case if you tried to *directly* measure the individual currents -- e.g., resistively -- and form the difference -- i.e., comparison -- algebraically) If you've ever examined a GFCI circuit breaker, you will note that it isnt the simple "two terminal" device of a regular (non GFCI) breaker. This is because the GFCI breaker has to have an additional "ground" connection (which a regular breaker doesn't need) usually implemented with a short pigtail (that you mechanically fasten to the panel's ground). GFCI *outlets* are dogs. They work the same way but are usually built of lesser quality components. Also, they are subject to more abuse (each time an appliance is plugged/unplugged). And, are often exposed to more environmental extremes than a GFCI breaker in a panel box. Also, note that there is no way a (typical) GFCI can "test itself" to determine that it is (likely) operational. So, a failure in the sense electronics can cripple the protection feature in a way that is not obvious to the user (i.e., the circuit still supplies "unprotected power"). Note that a GFCI offers no protection against an unintended load directly across the hot + neutral. I.e., if you wear rubber soled shoes (which is advisable when working with electricity) and accidentally touch hot *and* neutral, the circuit will gladly deliver its full rated capacity *through* your body -- as if you were a light bulb! :> OTOH, if you did NOT have rubber soled shoes on (or had some *other* path to "earth"), the GFCI *would* protect. (i.e., don't fall victim to the false sense of security that a GFCI protected circuit is somehow *safer* than a regular circuit!) Anything else you need to know? Wanna check my spelling? Or, my grammar??
From: Jamie on 28 Nov 2009 13:53 D Yuniskis wrote: > PeterD wrote: > >> On Fri, 27 Nov 2009 17:40:49 -0700, D Yuniskis >> <not.going.to.be(a)seen.com> wrote: >> >>> PeterD wrote: >>> >>>> On Mon, 23 Nov 2009 18:38:47 -0700, D Yuniskis >>>> <not.going.to.be(a)seen.com> wrote: >>>> >>>> >>>>> This is how GFCI breakers work -- they watch for current "leaking" >>>>> off to ground someplace other than in the "return" conductor. >>>> >>>> No they don't. They look for imbalanced current flow between the two >>>> conductors. >>> >>> Gee, isn't that what I *said*? >> >> >> No, you didn't. >> >>> How do you get an imbalance if >>> current isn't *leaking* off to ground someplace other than >>> in the "return" conductor? >> >> >> Re-read your post. > > > I don't have to re-read it -- I *wrote* it! > > A GFCI is nothing more than a tiny transformer with > "sense electronics" as its "load". The primary to the > transformer is the circuit being monitored. *BOTH* > conductors pass through the transformer. > > Since an alternating current generates a magnetic field, > that field couples *through* the transformer to the > *secondary* of the transformer -- which is the "sense > electronics". The field generated by the primary is > a function of the *net* current flowing through the > primary "winding" (winding can often be confusing in this > context as it is usually just a "single turn" -- as such, > it doesn't even go completely *around* the transformer's > core!). > > All of the current flowing *to* the INTENDED load (remember, > the GFCI can also see an *unintended* load!) goes through the > supply/hot lead, through the transformer's primary. All > of the current *returning* from the load passes through the > neutral/return conductor *also* through the transformer's > primary. > > If any of the supply current has "leaked" away via some > other path (to "ground") -- like through a person's body -- then > the current to and current from will not be equal. As > such, the magnetic fields generated by each conductor won't > *perfectly* cancel out. As a result, some energy will be > coupled across the transformer's core to its secondary. > > You can have a *lot* of gain across the transformer since > the secondary doesn't need much power to function. As such, > you can look for very small "leaks" even in circuits carrying > very *large* currents! I.e., aside from the physical size of > the transformer and the primary conductors passing through > it, a GFCI for a 1000A circuit is essentially the same as one > for a 20A "household" circuit. > > (N.B. this would not be the case if you tried to *directly* > measure the individual currents -- e.g., resistively -- and > form the difference -- i.e., comparison -- algebraically) > > If you've ever examined a GFCI circuit breaker, you will note > that it isnt the simple "two terminal" device of a regular > (non GFCI) breaker. This is because the GFCI breaker has to > have an additional "ground" connection (which a regular > breaker doesn't need) usually implemented with a short pigtail > (that you mechanically fasten to the panel's ground). > > GFCI *outlets* are dogs. They work the same way but are > usually built of lesser quality components. Also, they > are subject to more abuse (each time an appliance is > plugged/unplugged). And, are often exposed to more > environmental extremes than a GFCI breaker in a panel box. > > Also, note that there is no way a (typical) GFCI can "test > itself" to determine that it is (likely) operational. So, a > failure in the sense electronics can cripple the protection > feature in a way that is not obvious to the user (i.e., the > circuit still supplies "unprotected power"). > > Note that a GFCI offers no protection against an unintended > load directly across the hot + neutral. I.e., if you wear > rubber soled shoes (which is advisable when working with > electricity) and accidentally touch hot *and* neutral, > the circuit will gladly deliver its full rated capacity > *through* your body -- as if you were a light bulb! :> > OTOH, if you did NOT have rubber soled shoes on (or had > some *other* path to "earth"), the GFCI *would* protect. > (i.e., don't fall victim to the false sense of security > that a GFCI protected circuit is somehow *safer* than > a regular circuit!) > > Anything else you need to know? Wanna check my spelling? > Or, my grammar?? That's a very good run down :) Btw. there are Self testing GFCI's.. http://www.hubbell-wiring.com/Press/PDFS/H5185.pdf We use these extensively. Coast more, but what the hell. And those that get a little confused with the AGFCI units which are mostly in the modern GCFI receptacle, just not stated. Most don't know the difference. Those that don't have U-ground corded devices get confused when they still see their GFCI trip just from sliding in the plug. This only happens with the newer GFCI's that include the arc fault detection along with the ground fault current sense. I just love it when high powered R.F. disturbances trip those lovely AGFCI and AFB units :) I also like it when the installer removes what looks like excess neutral wire that's in a coil. by by RF choke. I haven't looked in a code book lately how ever, Since it's not designed to teach those about electricity, but just follow some guide lines for safety, I don't think there is an assert about the coil being present. This is done via the manufacturer for noise amuity. Not all may suggest to do this how ever, if you see it packaged in a coil, bets are, you should keep it that way or as much as possible. We have some Square-D line that will false trigger if you remove that coil form, in the plant.
From: D Yuniskis on 28 Nov 2009 14:46 Jamie wrote: > D Yuniskis wrote: > >> Also, note that there is no way a (typical) GFCI can "test >> itself" to determine that it is (likely) operational. So, a >> failure in the sense electronics can cripple the protection >> feature in a way that is not obvious to the user (i.e., the >> circuit still supplies "unprotected power"). > > Btw. there are Self testing GFCI's.. Really? I stand corrected (I will have to chase down the link to see how they work). Presumably, they test the sense electronics *while* disabling the "trip" function? (I can't see how else they could operate as you surely wouldn't want the circuit to open each time it tested itself :> ) In which case, I guess they hope that the circuitry that inhibits the trip never fails! :> > http://www.hubbell-wiring.com/Press/PDFS/H5185.pdf > > We use these extensively. Coast more, but what the hell. What sort of cost premium? Are they required for use in certain applications (medical, etc.)? Or, is it just "a nice feature to have"? > And those that get a little confused with the AGFCI units > which are mostly in the modern GCFI receptacle, just not > stated. Most don't know the difference. > > Those that don't have U-ground corded devices get confused when they > still see their GFCI trip just from sliding in the > plug. This only happens with the newer GFCI's that include the arc fault > detection along with the ground fault current sense. Ah, OK. So, I assume most modern electronic loads (i.e., things with line switchers in them like PC's) trip these often? > I just love it when high powered R.F. disturbances trip those lovely > AGFCI and AFB units :) RF as in *radiated* (not *conducted*)? Like someone keying a transceiver nearby? How close do they have to be (i.e. does this cause grief in actual *practice*)? > I also like it when the installer removes what looks like excess > neutral wire that's in a coil. by by RF choke. I haven't looked in a > code book lately how ever, Since it's not designed to teach those about > electricity, but just follow some guide lines for safety, I don't think > there is an assert about the coil being present. This is done via the > manufacturer for noise amuity. Not all may suggest to do this how ever, > if you see it packaged in a coil, bets are, you should keep it that way > or as much as possible. We have some Square-D line that will false > trigger if you remove that coil form, in the plant. Is it an air core or ferrite? In either case, it is fairly obvious (?) that this is something that is *meant* to be part of the assembly? (contrast that with a pigtail that just "happens" to be coiled up nicely for packaging)
From: Jamie on 28 Nov 2009 19:23 D Yuniskis wrote: > Jamie wrote: > >> D Yuniskis wrote: >> >>> Also, note that there is no way a (typical) GFCI can "test >>> itself" to determine that it is (likely) operational. So, a >>> failure in the sense electronics can cripple the protection >>> feature in a way that is not obvious to the user (i.e., the >>> circuit still supplies "unprotected power"). >> >> >> Btw. there are Self testing GFCI's.. > > > Really? I stand corrected (I will have to chase down the link > to see how they work). Presumably, they test the sense > electronics *while* disabling the "trip" function? (I > can't see how else they could operate as you surely wouldn't > want the circuit to open each time it tested itself :> ) > In which case, I guess they hope that the circuitry that > inhibits the trip never fails! :> > >> http://www.hubbell-wiring.com/Press/PDFS/H5185.pdf >> >> We use these extensively. Coast more, but what the hell. > > > What sort of cost premium? Are they required for use in > certain applications (medical, etc.)? Or, is it just > "a nice feature to have"? Just a nice feature, its not code to have one like this and also, code makes previsions for life saving equipment where is, you don't install one of these devices and the receptacle is suppose to be a coded color, if every one follows these rules ? I don't know. As far as cost ? I'm not the one that buys them how ever, been told they are not cheap compared to run of the mill versions. You must remember that anything from HUBBELL is going to have a premium on it. For example, the guys at work tell me it's cheaper to buy a cheap extension cord because just one HUBBELL device cost more than the whole cord!. So I guess if you factor in the other end , and wire, you have yourself an expensive extension cord. >> And those that get a little confused with the AGFCI units >> which are mostly in the modern GCFI receptacle, just not >> stated. Most don't know the difference. >> >> Those that don't have U-ground corded devices get confused when they >> still see their GFCI trip just from sliding in the >> plug. This only happens with the newer GFCI's that include the arc fault >> detection along with the ground fault current sense. > > > Ah, OK. So, I assume most modern electronic loads (i.e., > things with line switchers in them like PC's) trip these > often? Most devices that involve switchers, which of course generates noise, have their own common mode chokes that blocks out sufficient noise to prevent this. Some very older switch mode supplies may cause the AGFCI to fault how ever, at one time, and maybe you still can, you used to be able to purchase inline filters, which were nothing but common mode chokes. >> I just love it when high powered R.F. disturbances trip those lovely >> AGFCI and AFB units :) > > > RF as in *radiated* (not *conducted*)? Like someone keying > a transceiver nearby? How close do they have to be (i.e. does > this cause grief in actual *practice*)? Oh they have to be like driving by your home and it depends on the installation in the home it self. Service vehicles like police and fire that do not have a clean tail drop on their transmission can cause wide band interference and cause these arc breakers to trip. > >> I also like it when the installer removes what looks like excess >> neutral wire that's in a coil. by by RF choke. I haven't looked in a >> code book lately how ever, Since it's not designed to teach those about >> electricity, but just follow some guide lines for safety, I don't think >> there is an assert about the coil being present. This is done via the >> manufacturer for noise amuity. Not all may suggest to do this how ever, >> if you see it packaged in a coil, bets are, you should keep it that >> way or as much as possible. We have some Square-D line that will false >> trigger if you remove that coil form, in the plant. > > > Is it an air core or ferrite? In either case, it is fairly obvious (?) > that this is something that is *meant* to be part of the assembly? > (contrast that with a pigtail that just "happens" to be coiled > up nicely for packaging) The original Arc fault breaker never had a neutral wire supplied, you had to bond the N with the bar yourself. This didn't last long because installers were taking short cuts and not bonding them at all. Then, a neutral wire was supplied with each device but was just folded or big hand coiled for boxing. It was not to long afterwards they found out that RF was tripping these so, for quick fix, they started to ship them with the neutral wire coiled in a tight manner so that it could be install with most of the coil still in it's form. They had a small slip of paper in there suggesting the installation. The last time we saw a new box, they no longer ship any revision notes like that. SO, I guess it's assumed that most should know to keep the wire coiled and only undo what you need to reach the bar. To resolve issues where these coils have been cut out and you think there is an RFI issue. Electricians have installed large gauge chokes inline with the neutral that belongs to the AFB device. The last time I talked to my friend that is on the NEC code board, that gets together annually, he stated that these devices are still being battled out among the committee and electrical Engineers etc.. no 2 sides can come to an agreement. go figure. I know that we had big issues using them at work on HI-POT devices that are mounted near a water source. The very nature of the device itself is design to hit ground when a fault occurs, which takes out the GFCI circuit. We had to install isolation transformer service for each one of these devices to prevent a ground current loop to develop between the neutral and ground.
From: David Brodbeck on 1 Dec 2009 17:03
D Yuniskis wrote: >> I just love it when high powered R.F. disturbances trip those lovely >> AGFCI and AFB units :) > > RF as in *radiated* (not *conducted*)? Like someone keying > a transceiver nearby? How close do they have to be (i.e. does > this cause grief in actual *practice*)? I had one that would trip on SSB voice peaks. The antenna was a full-wave 28 MHz loop on the balcony. Power output was about 25 watts PEP. It was mostly my fault. I had no station ground (2nd floor apartment), and I was feeding the loop directly with coax, which is not a recipe for a well matched or well balanced antenna setup. I probably had RF conducting back on the shield and getting into everything, including the power wiring. |