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Homeowner Forum / Construction / October 2006GFCI operation question
the way a GFCI functions, would it trip if a bad connection were made to it ? (if say, a terminal with the hot or neutral wasn't screwed down tight & a plugged in load drew current causing the terminal to warm up - would the GFCI trip ?) http://ts.nist.gov/ts/htdocs/210/gsig/apec-elec/gannon.ppt The load's current use is sensed by the GFCI whether wired dubiously as in the example you imposed. The problem child is when the grounding and neutral are swapped. Arcing, as implied by your example, needs an AFI circuit for detection.  SignatureJonny > > the way a GFCI functions, would it trip [quoted text clipped - 5 lines] > the terminal to warm up - would the > GFCI trip ?) > http://ts.nist.gov/ts/htdocs/210/gsig/apec-elec/gannon.ppt > [quoted text clipped - 13 lines] > > the terminal to warm up - would the > > GFCI trip ?) thanks everyone for the responses. the powerpoint link was very informative. if i understood it correctly, any current differential > 5ma between hot & neutral would cause a trip. if one terminal has contact resistance (loose), wouldn't the current flow on that leg be reduced by the amount of resistance ? and therefore trip the GFCI ? (since it would see less on one leg, vs the other - or am I misinterpreting, since a hot/load/neutral circuit is basically in series, and current is only depended on how much the device draws?) >> http://ts.nist.gov/ts/htdocs/210/gsig/apec-elec/gannon.ppt >> [quoted text clipped - 31 lines] > and current is only depended on how much the > device draws?) Both wires are part of the same series circuit and the current will be the same whileever there is no other path (ground). Current in = current out. The resistance of the contact will be part of the impedance (along with the real load) that determines the magnitude of the current. SignatureJohn G Wot's Your Real Problem? >the way a GFCI functions, would it trip >if a bad connection were made to it ? [quoted text clipped - 4 lines] > the terminal to warm up - would the > GFCI trip ?) I don't think so. Why would the resistance of a bad connection be any different from the resistance of a light bulb. I wouldn't assume there will be arcing just because a connection isn't tight enough. So I wouldn't assume that even an arc fault circuit breaker would be tripped by a loose connection. Am I right or wrong? >> the way a GFCI functions, would it trip >> if a bad connection were made to it ? [quoted text clipped - 11 lines] > tight enough. So I wouldn't assume that even an arc fault circuit > breaker would be tripped by a loose connection. Am I right or wrong? Methos A GFIC is made to trip on sudden line voltage changes. A slow warm up would not trip the built in breaker. This very problem cause a house fire that burned a third of my parents house to the ground. Two wires in some old Romex touched and caused a slow short but it was not enough to trip the breakers. Therefore, it warmed up long enough to catch fire. GFIC's are a nice safety feature but it certainly doesn't catch all problems >>> the way a GFCI functions, would it trip >>> if a bad connection were made to it ? [quoted text clipped - 4 lines] >>> the terminal to warm up - would the >>> GFCI trip ?) I agree with others that a GFCi wouldn't trip on a loose connection. >> I don't think so. Why would the resistance of a bad connection be any >> different from the resistance of a light bulb. >> >> I wouldn't assume there will be arcing just because a connection isn't >> tight enough. So I wouldn't assume that even an arc fault circuit >> breaker would be tripped by a loose connection. Am I right or wrong? A loose connection can produce enough heat to start a fire without arcing (a "glowing" connection). Late stages in failure are likely to arc. AFCIs sense "parallel" arcs - from hot-to-neutral (a "fault", the F in AFCI). Starting in 2008 the NEC requires them to also detect "series" arcs, as in a loose connection. As far as I know, no current AFCIs detect series arcs, so none would detect a loose connection. > Methos > [quoted text clipped - 6 lines] > GFIC's are a nice safety feature but it certainly doesn't catch all > problems GFCIs trip on a difference in current between the hot and neutral, not line voltage changes. They are primarily for electrocution protection. The "slow short" you describe, an arc that trips a breaker slowly, if at all, is exacty what AFCIs are designed to protect against. A more likely cause is probably an abused extension cord. AFCIs also include 30mA ground fault protection (GFCIs have 5mA protection). The idea is, I think, that if a ground wire is adjacent, a hot-to-neutral arc is likely to also become hot-to-ground. bud-- >>>> the way a GFCI functions, would it trip >>>> if a bad connection were made to it ? [quoted text clipped - 46 lines] > > bud-- Methos It sounds like bud has the right answer. I hadn't heard about the upcoming AFIC's but will certainly pass the info on to everyone at my office (I'm a construction administrator for a large architectural firm). Thanks bud for the education. LightsAREon I don't believe it's "upcoming". I think that all AFCI's currently have 30ma ground fault protection for equipment. > Methos > I hadn't heard about the upcoming AFIC's but will certainly pass the info > on to everyone at my office (I'm a construction administrator for a large > architectural firm). Thanks bud for the education. > LightsAREon What is "30ma ground fault protection"? It takes less then 30 mA to kill a man. >I don't believe it's "upcoming". I think that all AFCI's currently have >30ma ground fault protection for equipment. [quoted text clipped - 4 lines] >> architectural firm). Thanks bud for the education. >> LightsAREon On Mon, 28 Aug 2006 16:53:37 -0700, "Ook" <Ook Don't send me any freakin' spam at zootal dot com delete the Don't send me any freakin' spam> wrote: >What is "30ma ground fault protection"? It takes less then 30 mA to kill a >man. They call it Ground-Fault Protection of Equipment when it is at the 30ma level. BTW get used to AFCIs. They will be on all 120v 15 and 20a circuits in a dwelling in 2008 if the code goes as drafted. Comments are still open until October. > On Mon, 28 Aug 2006 16:53:37 -0700, "Ook" <Ook Don't send me any > freakin' spam at zootal dot com delete the Don't send me any freakin' [quoted text clipped - 5 lines] > They call it Ground-Fault Protection of Equipment when it is at the > 30ma level. Yea - it is to detect the arc, not protect people. AFCIs can have a 5 mA ground fault trip and be used as both AFCI and GFCI. It would require 2 test buttons. Probably would see them if the code change below goes into effect. To PPS - I presume "upcoming" is the requirement to detect "series" arcs starting 2008, not 30mA ground fault trip. > BTW get used to AFCIs. They will be on all 120v 15 and 20a circuits > in a dwelling in 2008 if the code goes as drafted. Comments are still > open until October. Considering the new AFCIs aren't on the market (or are they recently out?), and it is only about 1.5 years for field experience until they are required in 2008, it seems like requiring the new AFCIs in all 15/20A dwelling circuits is not a great idea (whatever the wisdom of requiring the current AFCIs is). Bet there are plenty of comments on that code change. An interesting piece on AFCIs, including why normal breakers are inadequate for arcs and arcs that shouldn't trip them is at: http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf bud-- >On Mon, 28 Aug 2006 16:53:37 -0700, "Ook" <Ook Don't send me any >freakin' spam at zootal dot com delete the Don't send me any freakin' [quoted text clipped - 7 lines] >in a dwelling in 2008 if the code goes as drafted. Comments are still >open until October. Wouldn't that be all circuits in new construction? SignatureMark Lloyd http://notstupid.laughingsquid.com "Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well armed lamb contesting the vote." - Benjamin Franklin >Wouldn't that be all circuits in new construction? Usually it would be all the 120v ones. >>Wouldn't that be all circuits in new construction? > >Usually it would be all the 120v ones. There's no 240v AFCIs? SignatureMark Lloyd http://notstupid.laughingsquid.com "Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well armed lamb contesting the vote." - Benjamin Franklin >>>Wouldn't that be all circuits in new construction? >> >>Usually it would be all the 120v ones. > >There's no 240v AFCIs? I believe there may be 240v AFCIs but they are not mandated in the code yet. Only requirement I'm aware of where GFPE's (30 ma GFCI) are required in the 2005 NEC is Section 426.28. > What is "30ma ground fault protection"? It takes less then 30 mA to kill a > man. >A loose connection can produce enough heat to start a fire without >arcing (a "glowing" connection). Late stages in failure are likely to arc. [quoted text clipped - 27 lines] > >bud-- What is an AFIC? Thanks! David [snip] >What is an AFIC? An Arc Fault Interrupted Circuit. A circuit that has no current in it because you didn't use an AFCI, your house was on fire, and the fire department cut off the power. >Thanks! > >David >>A loose connection can produce enough heat to start a fire without >>arcing (a "glowing" connection). Late stages in failure are likely to arc. [quoted text clipped - 33 lines] > > David Arc Fault Circuit Interrupter. The AFCI breakers look like, and wire like GFCIs. AFCIs trip on arcs. The NEC requires them on new circuits to bedrooms. The proposed 2008 NEC requires them for all residential 15 and 20A circuits IIRC (could still be changed though). A good paper from the Consumer Product Safety Commission on AFCIs is at http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf It explains the rationalle for using AFCIs describes how they work. bud-- In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: | Arc Fault Circuit Interrupter. The AFCI breakers look like, and wire | like GFCIs. AFCIs trip on arcs. The NEC requires them on new circuits to | bedrooms. The proposed 2008 NEC requires them for all residential 15 and | 20A circuits IIRC (could still be changed though). And AFCI-only device could be made to work without accessing the neutral of the circuit involved. The issue is the AFCI device needs to use power to function. Possibly that is the only purpose of the neutral pigtail if the device does not include any GFCI function. I hope the change goes through. But I would like to see local AHJ rules that permit case-by-case exceptions to be made where AFCI devices are found to be incompatible with certain appliances. And regarding the issue of putting smoke detectors on AFCI protected circuits. The simple solution is keep receptacle circuits and lighting circuits separate, and put the smoke detectors on the lighting circuits. Those circuits should have much less instance of nuisance trips, and would more readily be noticed if they are opened, in case the smoke detector false to alarm. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-09-26-0455@ipal.net | |------------------------------------/-------------------------------------| > And regarding the issue of putting smoke detectors on AFCI protected > circuits. The simple solution is keep receptacle circuits and lighting > circuits separate, and put the smoke detectors on the lighting circuits. > Those circuits should have much less instance of nuisance trips, and > would more readily be noticed if they are opened, in case the smoke > detector false to alarm. We had to have smoke detectors on a separate dedicated circuit. Our contractor decided not to sub out the electrical work, and sure looked upset when he learned he had to rewire four levels of smoke detectors. S > In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: > [quoted text clipped - 7 lines] > to function. Possibly that is the only purpose of the neutral pigtail if > the device does not include any GFCI function. But all AFCIs include a 30mA GFCI as part of the protection. (That is not the same as a 6mA GFCI for shock protection of people.) > And regarding the issue of putting smoke detectors on AFCI protected > circuits. The simple solution is keep receptacle circuits and lighting > circuits separate, and put the smoke detectors on the lighting circuits. > Those circuits should have much less instance of nuisance trips, and > would more readily be noticed if they are opened, in case the smoke > detector false to alarm. Just to be clear, lighting circuits that include bedrooms have to be on an AFCI. (I think that is what you said.) bud-- In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: |> In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: |> [quoted text clipped - 10 lines] | But all AFCIs include a 30mA GFCI as part of the protection. (That is | not the same as a 6mA GFCI for shock protection of people.) I've seen some that don't. Those were from Cutler-Hammer, the company that makes AFCI without GFCI, AFCI with 30maGFCI, and AFCI with 6maGFCI. If the NEC ends up requiring the GFCI function, then the ones without GFCI would likely end up being no longer made. But right not it is not clear what the NEC requires NOW (2005 code) or will require (2008 code). All we know is that the scope of where AFCI is required appears to be expanding. |> And regarding the issue of putting smoke detectors on AFCI protected |> circuits. The simple solution is keep receptacle circuits and lighting [quoted text clipped - 5 lines] | Just to be clear, lighting circuits that include bedrooms have to be on | an AFCI. (I think that is what you said.) All the circuits supplying outlets in the bedrooms must be AFCI protected. The issue with smoke detectors is more complex. I do believe they must be on AFCI, and I think that is appropriate. I do not expect the smoke detectors to be any source of nuisance trips. Thus it might seem to be a good plan to put them all on their own circuit. But I don't trust that they will alarm when the power is lost. The reason is because that would cause problems in utility outages. Do you want all your smoke detectors beeping when a storm knocks out your power? But what if the branch circuit the smoke detectors are on loses power. You might not even notice that a problem exists. Connecting smoke detectors with receptacles is a bad idea becauseof two reasons. Either the receptacle might not even get used, or the receptacle's usage might be the source of excess nuisance trips. That could compromise the safety of the smoke detectors. My idea is to put them on the same circuit as regularly used overhead lights, such as hall lights or stairway lights. That way, if there is a circuit trip that does affect the smoke detectors, you will be alerted to a problem with that breaker, and motivated to correct it. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-09-27-1544@ipal.net | |------------------------------------/-------------------------------------| > In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: > |> In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: [quoted text clipped - 49 lines] > affect the smoke detectors, you will be alerted to a problem with that > breaker, and motivated to correct it. Smoke detectors that are designed to be interconnected will usually have a backup battery and will chirp every so often if power is lost. SignatureTom Horne Well we aren't no thin blue heroes and yet we aren't no blackguards to. We're just working men and woman most remarkable like you. >> In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: >> |> In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: [quoted text clipped - 15 lines] >> I've seen some that don't. Those were from Cutler-Hammer, the company >> that makes AFCI without GFCI, AFCI with 30maGFCI, and AFCI with 6maGFCI. Have a reference handy for AFCIs without 30mA ground fault detection? >> If the NEC ends up requiring the GFCI function, then the ones without >> GFCI would likely end up being no longer made. But right not it is not [quoted text clipped - 36 lines] >> affect the smoke detectors, you will be alerted to a problem with that >> breaker, and motivated to correct it. (There was a proposal for the 2008 NEC to require that but it was rejected.) > Smoke detectors that are designed to be interconnected will usually have > a backup battery and will chirp every so often if power is lost. Do they chirp if the battery is dead? Removed? I havn't played with them. The way I understand the 2008 NEC-ROP, NFPA 760 requires smoke detectors that are on AFCI circuits have a secondary power source (battery). Another hidden requirement. IMHO requiring smoke detectors to be on an AFCI circuit lowers overall fire safety and is dumb. bud-- In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: | Have a reference handy for AFCIs without 30mA ground fault detection? Some have 5ma GFCI and some have no GFCI: Page 22: http://www.eatonelectrical.com/unsecure/cms1/TB00300001E.PDF Pages 3 and 4: http://www.eatonelectrical.com/unsecure/cms1/TD00308001E.PDF Page 1: http://www.eatonelectrical.com/unsecure/cms1/TD01201036E.PDF | The way I understand the 2008 NEC-ROP, NFPA 760 requires smoke detectors | that are on AFCI circuits have a secondary power source (battery). | Another hidden requirement. | | IMHO requiring smoke detectors to be on an AFCI circuit lowers overall | fire safety and is dumb. I'm not convinced of that, yet. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-09-28-0650@ipal.net | |------------------------------------/-------------------------------------| Those without GFCI protection are intended for use in habitable and non-habitable spaces not requiring ground fault protection (living rooms and the like.) Those with 5ma GFCI protection are intended to serve bathrooms, kitchens and anywhere where a standard GFCI is required. Those with 30ma GFCI is designed to serve residential equipment noted in the NEC requiring 30 ma GFCI (actually termed GFEP to differentiate between the two.) Article 426.28 only requires ground fault protection for equipment, no personnel and that's to only place it can be used to meet code. To protect personnel, you must use 5ma protection. > In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: > > | Have a reference handy for AFCIs without 30mA ground fault detection? > > Some have 5ma GFCI and some have no GFCI: In alt.engineering.electrical PPS <webmaster@npcc.net> wrote: | Those without GFCI protection are intended for use in habitable and | non-habitable spaces not requiring ground fault protection (living rooms and [quoted text clipped - 8 lines] | personnel and that's to only place it can be used to meet code. To protect | personnel, you must use 5ma protection. This is along the lines of what I expected, and certainly sounds very reasonable. Still, the required ground fault protection can be had with an AFCI that has no GFCI, or only has 30ma GFCI, as long as the 5ma GFCI receptacles are also used, where the GFCI people protection is required. Whether one would want to do it that way is another matter. In a bathroom, there is an advantage to having the ability to reset the GFCI device right there. That advantage may or may not be relevant for a kitchen. Other areas like a garage are probably not much of a concern. I have been told, but have never sacrificed a device to verify, or set up the appropriate test, that GFCI receptacles open BOTH the hot wire AND the neutral wire when they trip. If so, why is that? Is it to offer at least some protection even when the device is miswired? Or is there even some risk with voltages on the neutral wire? I do believe some neutral wire risk exists. It's certainly not as much as for the hot wire, usually in terms of voltage, and in terms of exposure events. One example of when the risk is high is when there is a open in in the supply neutral. But the chance of that happening coincident with contacting the neutral to ground, is much lower than either alone. The other risk is the voltage present as a function of the voltage drop along the supply neutral from the point of bonding to the point of contact. That's generally a very low voltage, though it can vary with loading on the system. Still, I'd feel safer having an interruption mechanism that will open BOTH wires together when tripped. Suppose you have an AFCI that includes GFCI protection, either at the 5ma level or the 30ma level, followed by a GFCI receptacle. Leakage from the neutral to ground would still result in a trip. But can it be guaranteed that the receptacle device will always open? Perhaps the breaker will open first, and de-energize the circuit before the receptacle can open, leaving the neutral wire still connected. To be assured that the receptacle will trip, I'd have to have no GFCI in the breaker, and place the GFCI protection in the receptacle, assuming it is designed to open the neutral. If I am forced to put GFCI protection in the breaker along with the AFCI protection, or if GFCI receptacles don't actually have neutral contacts that can be opened, I do have a fallback plan. I would run the circuit through a secondary box containing a 2-pole normally open electrically closed contactor. The circuit would run through these contacts. The coil would be powered from the supply side. If the breaker opens the hot wire, the coil will de-energize and open both wires. It won't be as quick an open since such contactors aren't listed for GFCI protection. But at least it will be something that can prevent certain problems. For shared neutral circuits, this would be a 3-pole contactor with a 240 volt coil. These are avalable from Square-D and Cutler-Hammer. One issue that some people might be concerned with is the constant power used by the coil, 24x365xN. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-09-28-1854@ipal.net | |------------------------------------/-------------------------------------| > In alt.engineering.electrical PPS <webmaster@npcc.net> wrote: > [quoted text clipped - 10 lines] > | personnel and that's to only place it can be used to meet code. To protect > | personnel, you must use 5ma protection. 30mA ground fault detection in an AFCI is for arc protection. Far as I know all AFCIs include it (though I need to look harder at phil's 2nd link). Arcs can produce carbon paths which, if a ground is available, can produce ground fault currents. That may produce a trip before there is an arc or before an arc is detected. In the Consumer Product Safety Commission paper at: http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf that is explained on pdf page 14. Phil has a link in another thread to: http://www.eatonelectrical.com/unsecure/cms1/AFCI_UL_SPECIAL_SERVICES_INVESTIGAT ION.PDF which is a UL investigation showing that a "glowing connection" at a receptacle binding screw may (or may not) cause an AFCI trip through the 30mA ground fault function. > This is along the lines of what I expected, and certainly sounds very > reasonable. Still, the required ground fault protection can be had with [quoted text clipped - 11 lines] > some protection even when the device is miswired? Or is there even some > risk with voltages on the neutral wire? I have read in newsgroups (so it must be true) that both poles are opened for hot-neutral-reverse protection. GFCIs (5mA) are now required to not work with reverse load-line terminal wiring. (Previously the load terminals connected to the receptacle.) I don't think you can do that without double pole contacts line-receptacle and line-load. And I don't think it can be done without that being a NO contact that requires the device to be powered to connect (which it wouldn't be if the line-side neutral was open). In both cases testing can be easily done without a hammer but so far I have been too lazy. > I do believe some neutral wire risk exists. It's certainly not as much as > for the hot wire, usually in terms of voltage, and in terms of exposure [quoted text clipped - 15 lines] > trip, I'd have to have no GFCI in the breaker, and place the GFCI protection > in the receptacle, assuming it is designed to open the neutral. bud-- > 30mA ground fault detection in an AFCI is for arc protection. Far as I > know all AFCIs include it (though I need to look harder at phil's 2nd > link). Here's a good place to learn more. http://www.cpsc.gov/CPSCPUB/PUBS/afcifac8.pdf#search=%22afci%20ground%20fault%22 In alt.engineering.electrical PPS <webmaster@npcc.net> wrote: |> 30mA ground fault detection in an AFCI is for arc protection. Far as I |> know all AFCIs include it (though I need to look harder at phil's 2nd |> link). | | Here's a good place to learn more. | http://www.cpsc.gov/CPSCPUB/PUBS/afcifac8.pdf#search=%22afci%20ground%20fault%22 Sounds like we are now back to the beginning. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-09-30-0748@ipal.net | |------------------------------------/-------------------------------------| A "neutral" is not defined in the NEC, but is described in Article 310.15(B)(4) as carrying "only the unbalanced current from other conductors...". In a 120 volt (lighting) circuit, the current is carried on both the white (or "grounded") conductor and an "ungrounded (usually black, but not necessarily) conductor. The term "neutral" refers to the neutral connection at the transformer; the center-tap. In a pure 240 volt circuit, current flows on the two phase conductors and a white (or grounded) conductor in not even needed. By introducing 120 volt circuits, the white forms one of the return legs, and carries current. (240 v between the ungrounded legs, 120 v from either leg to the neutral.) In Europe, the term "neutral" does include a grounded conductor in a 120 v circuit. In the states the term is used interchangeably but in error. > In alt.engineering.electrical PPS <webmaster@npcc.net> wrote: > | [quoted text clipped - 14 lines] > | > |------------------------------------/-------------------------------------| In alt.engineering.electrical PPS <webmaster@npcc.net> wrote: | A "neutral" is not defined in the NEC, but is described in Article | 310.15(B)(4) as carrying "only the unbalanced current from other | conductors...". "Neutral conductor" is defined in the NEC. The term is used in many places. I fully understand what a neutral is. Are you raising an issue about its common or formal usage? | In a 120 volt (lighting) circuit, the current is carried on both the white | (or "grounded") conductor and an "ungrounded (usually black, but not | necessarily) conductor. If you are wanting to get very specific, it's the insulators that have the color. The current is carried on the (usually) copper metal (with a magnetic field, of course). The code requires the grounded conductor be identified well (e.g. continuous color, not just marked at each end). Others have more leeway. | The term "neutral" refers to the neutral connection at the transformer; the | center-tap. In a pure 240 volt circuit, current flows on the two phase | conductors and a white (or grounded) conductor in not even needed. By | introducing 120 volt circuits, the white forms one of the return legs, and | carries current. (240 v between the ungrounded legs, 120 v from either leg | to the neutral.) You could tap the transformer off-center a bit if you wanted to and have 115 volts on one side and 125 volts on the other side. Would you call that a "neutral"? So tell me ... what happens if you have a couple of very low power factor loads, one on each 120 volt side, where one is very inductive and the other is very capacitive? Now how much current flows on the "neutral"? | In Europe, the term "neutral" does include a grounded conductor in a 120 v | circuit. In the states the term is used interchangeably but in error. I see very little use in error in the US. Neutral does not mean grounded, but it generally implies that because that is the required way to wire it up. See NEC 250.26(2). The two terms "neutral conductor" and "grounded conductor" do have different meanings, but are associated with the same wire because that is the required way. Single phase in Europe is generally 2-wire service. You can still call one wire neutral because it may well be the wire connected to the real neutral point in either a single phase transformer (center tapped 230/460) or a three phase transformer (connected to the star common). But it is grounded and thus (also) correct to call it a grounded conductor. If the service is coming from a 2-wire transformer all by itself, then it's not really neutral; it's just grounded. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-10-04-0750@ipal.net | |------------------------------------/-------------------------------------| > In Europe, the term "neutral" does include a grounded conductor in a 120 v > circuit. In the states the term is used interchangeably but in error. In Europe, there are no 120V circuits, and "neutral" is a supply current carrying conductor which is at or near ground potential. SignatureAndrew Gabriel In alt.engineering.electrical Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote: |> In Europe, the term "neutral" does include a grounded conductor in a 120 v |> circuit. In the states the term is used interchangeably but in error. | | In Europe, there are no 120V circuits, and "neutral" is a supply | current carrying conductor which is at or near ground potential. But that doesn't really change the meaning's origin. The first power systems were three phase to drive motors. I don't know if delta was used much way back when, but with star/wye configurations, you do have a genuine neutral. When single phase at 240v is taken from that, the neutral is still there. It just doesn't have enough phases brought in to take the neutralizing role there. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-10-05-0547@ipal.net | |------------------------------------/-------------------------------------| > In alt.engineering.electrical Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote: >|> In Europe, the term "neutral" does include a grounded conductor in a 120 v [quoted text clipped - 9 lines] > neutral is still there. It just doesn't have enough phases brought > in to take the neutralizing role there. The neutral role is still there, i.e. it's still at or near ground potential. Now there are some single phase supplies in europe which don't have a neutral, but they are much less common and only in a few countries (not UK). An example is a single phase supply from a corner grounded delta, where both of the lines are taken from a non-grounded corner. There are also IT supplies which are isolated with just a resistance to ground to prevent the secondary capacitively floating up to the much higer primary voltage. Strictly the side with the resistor to ground is still called a neutral, although it might be some way from ground potential. Again, I believe some parts of Europe use this, but it only occurs in the UK on standalone generators, not from the public supply. SignatureAndrew Gabriel In alt.engineering.electrical Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote: |> In alt.engineering.electrical Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote: |>|> In Europe, the term "neutral" does include a grounded conductor in a 120 v [quoted text clipped - 12 lines] | The neutral role is still there, i.e. it's still at or near ground | potential. But that's not what the meaning of neutral is. It's neutral whether it is grounded or not. In cases where there are 2 or mroe phases, the idea is that when things are in balance, there is no current on the neutral. It was neutralized by the balance. But I think the meaning really comes from the neutral point in the transformer winding of the secondary. | Now there are some single phase supplies in europe which don't have | a neutral, but they are much less common and only in a few countries | (not UK). An example is a single phase supply from a corner grounded | delta, where both of the lines are taken from a non-grounded corner. Apparently these are older connections. From what I gather, the first power in much of Europe in the late 1800's was 220/127 three phase. It appears that predated Edison supplying light to New York, so it seems he took the 220 voltage and split it for DC. He likely also realized, in all his light bulb work, that a lower voltage worked better on the filament. I've heard that the 220/127 can still be found in some remote locations like way north Norway and rural parts of Spain. A friend has reported seeing the remnants of 220/127 wiring in buildings in Germany predating WW1. | There are also IT supplies which are isolated with just a resistance | to ground to prevent the secondary capacitively floating up to the [quoted text clipped - 3 lines] | but it only occurs in the UK on standalone generators, not from the | public supply. The reason they use that resistance instead of a solid ground is to avoid single fault failures. But during that time, one hot line is now grounded. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-10-05-1237@ipal.net | |------------------------------------/-------------------------------------| [snip] >GFCIs (5mA) are now required to not work with reverse load-line terminal >wiring. Even when that's exactly what you want. > (Previously the load terminals connected to the receptacle.) I >don't think you can do that without double pole contacts line-receptacle [quoted text clipped - 4 lines] >In both cases testing can be easily done without a hammer but so far I >have been too lazy. [snip] Signature87 days until the winter solstice celebration Mark Lloyd http://notstupid.laughingsquid.com "The government of the United States is not, in any sense, founded on the Christian religion." -- George Washington > [snip] > >>GFCIs (5mA) are now required to not work with reverse load-line terminal >>wiring. > > Even when that's exactly what you want. When the supply wires are connected to the LOAD terminals on old GFCIs, the GFCI receptacle is not protected - it is live even if the GFCI is tripped. (I believe the downstream circuit, which would be connected to the LINE terminals, is protected.) Under the new UL standard, which I think was adopted about 2 years ago, if you connect supply wires to the LOAD terminals the GFCI receptacle and LOAD terminals will always be dead. I may have tried to say that with too few words. bud-- >> [snip] >> [quoted text clipped - 7 lines] >tripped. (I believe the downstream circuit, which would be connected to >the LINE terminals, is protected.) Which is what I wanted. This GFCI is installed inside (where no GFCI protection is needed) and it controls an outside light. The GFCI acts as a light switch (at least it used to, before I had to replace it with one of those "improved" ones). >Under the new UL standard, which I think was adopted about 2 years ago, >if you connect supply wires to the LOAD terminals the GFCI receptacle [quoted text clipped - 3 lines] > >bud-- Signature86 days until the winter solstice celebration Mark Lloyd http://notstupid.laughingsquid.com "The government of the United States is not, in any sense, founded on the Christian religion." -- George Washington In alt.engineering.electrical Bud-- <remove.BudNews@isp.com> wrote: |> [snip] |> [quoted text clipped - 13 lines] | | I may have tried to say that with too few words. Someone once told me that the GFCI receptacles that I found were DANGEROUSLY susceptible to strong radio fields, must have been wired in reverse. But I do know they did cut off the power to its own outlets, so I am convinced that they were wired correctly. Maybe they are defective products and the internal solenoid that trips the mechanism was wired on the LINE side and should have been wired on the LOAD side. What happens is that when a strong radio field is introduced, the GFCI sees this somehow as leakage current. Other than for it being the wrong frequency this is understandable, as the induced currents would be in common mode, with the same direction on hot and neutral. The DANGEROUS part is that even though the solenoid has opened the circuit and cut off the power from the outlets (and presumably upstream, which was not present for the ones I did this with), as long as the radio current was present, the solenoid continued to activate. I believe that these solenoids would be operating from the 120 volts AND are not designed for the heat that would result from continuous operation. They would have been designed with the idea in mind that as soon as the circuit opened, the leakage current would no longer be present. This creates TWO hazard conditions. The first is that if a radio field that caused this was external, it might not be known to the radio operator that there was a problem. It could cause the solenoid to overheat, melt insulation, short circuit, arc, catch fire, burn the house down, and KILL PEOPLE. I did NOT leave the radio field on for a long period of time when I did this test. Even for the very first time I discovered this, the loud buzzing of the solenoid in the GFCI was loud enough to get my quick attention and realize the radio was triggering the problem. So I was never doing this for more than a second or two. The second hazard exists if the GFCI breaker does NOT open the neutral. A neutral could have some low voltages present as a result of voltage drop between various L-N 120 volt loads and the point of bonding neutral to ground. A short circuit from neutral to ground might not have a great spectacular arc flash, but it could draw enough current to activate a GFCI at the 5ma level. The type of GFCI that allowed the radio current to trip the solenoid continuously would also result in continuous activation of the solenoid in this neutral-only leakage situation because the neutral would not be opened, and the GFCI control circuitry would still be powered. I believe a proper GFCI design must cut off its own power when tripped, so it is not doing a continuous trip. This could be done by powering the GFCI control circuitry, including the solenoid, from the LOAD side. When I suggested this in a posting somewhere a long time ago, someone said that it may be needed to power the solenoid from the LINE side to ensure that it completes its operation to full open the contacts. I can agree that leaving the contacts stuck in a partial open state where they may arc across is not a good thing. But this should be accomplished through the mechanical energy stored in the unfatiguable spring mechanism that gets charged when the unit is reset. The solenoid should just be releasing that spring. DO NOT DO THIS AT HOME OR WORK. There is the risk that some of these units may be so defective that even a short period of operation could result in substantial damage. I also do not know if GFCI breakers have this risk. If their internal circuitry remains energized from the bus contacts in the panel, a radio field could cause the very same problem. Although they clearly do have the proper spring loading mechanism, being a part of a circuit breaker, the solenoid that releases that mechanism when leakage current is detected would potentially be under continuous operation if the power remains and the apparent leakage issue remains. This would not only be a problem with a continuous radio field, but it could also be a problem when the neutral has enough voltage to make a leak to ground, such as in a subpanel. So DO NOT DO THIS NEAR A BREAKER PANEL. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-09-30-1853@ipal.net | |------------------------------------/-------------------------------------| > What happens is that when a strong radio field is introduced, the GFCI > sees [quoted text clipped - 3 lines] > with > the same direction on hot and neutral. It is more likely that the rf is getting into the GFCI electronics directly, rather than through the toroid. I suspect the input to the chip is fairly high impedance, and there may even be some non-linearity that acts as a detector. I know you have mentioned this before, and although I have never experienced it, I can easily believe that it can happen. I might try some experiments to replicate it. Do you have any idea of how strong and at what frequency the rf was? Ben Miller SignatureBenjamin D. Miller, PE B. MILLER ENGINEERING www.bmillerengineering.com > I have been told, but have never sacrificed a device to verify, or set up > the appropriate test, that GFCI receptacles open BOTH the hot wire AND the > neutral wire when they trip. If so, why is that? Is it to offer at least > some protection even when the device is miswired? Or is there even some > risk with voltages on the neutral wire? Just opens the ungrounded conductor, not the ground (mistakenly called a neutral). It uses a special transformer to measure the current on the grounded and ungounded lines, and if they are not the same (within 5ma) it trips; assums that the lost current is leaking to ground somewhere (possibly through a person). > I do believe some neutral wire risk exists. It's certainly not as much as Although the grounded conductor carries the same current as the ungrounded (white or identified) conductor (a white wire is only a neutral in a 120/240 volt circuit, and carrys the unblanced load of the 120/240 volt applaince), it's at the same potential as you are. Both are grounded to the earth and (hopefully) there is no potential difference when a person contacts the white wire; threrefor no shock hazzard (under normal conditions, IE wired properly in the first place.) In alt.engineering.electrical PPS <webmaster@npcc.net> wrote: |> I have been told, but have never sacrificed a device to verify, or set up |> the appropriate test, that GFCI receptacles open BOTH the hot wire AND the [quoted text clipped - 7 lines] | trips; assums that the lost current is leaking to ground somewhere (possibly | through a person). So you are the first to contradict the others and say this? I know how they work. The issue is whether the groundED conductor, commonly known as the neutral, is opened as well. |> I do believe some neutral wire risk exists. It's certainly not as much as | [quoted text clipped - 5 lines] | white wire; threrefor no shock hazzard (under normal conditions, IE wired | properly in the first place.) Not quite true. The neutral (I don't know why you are caling it ungrounded) is NOT at exactly the same potential as ground. If it were, we'd have never had to have a separate groundING/EGC wire. The fact is, the neutral CAN be at potentials above the earth for various reasons. In most cases it will be just a few volts or a fraction of a volt due to voltage drop. In fault cases, it can be more serious. In open neutral cases it can be very serious. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-09-30-0750@ipal.net | |------------------------------------/-------------------------------------| >>I have been told, but have never sacrificed a device to verify, or set up >>the appropriate test, that GFCI receptacles open BOTH the hot wire AND the [quoted text clipped - 4 lines] > Just opens the ungrounded conductor, not the ground (mistakenly called a > neutral). The grounding conductor is irrelevant to GFCI operation. Both the neutral and the hot are interrupted when a GFCI receptacle trips. It uses a special transformer to measure the current on the > grounded and ungounded lines, and if they are not the same (within 5ma) it > trips; assums that the lost current is leaking to ground somewhere (possibly [quoted text clipped - 5 lines] > (white or identified) conductor (a white wire is only a neutral in a 120/240 > volt circuit, and carrys the unblanced load of the 120/240 volt applaince), You have the above mis-identified. The neutral *is* the groundED conductor. The UNgrounded conductor is (a.k.a. "hot") NOT the white conductor, unless the circuit is miswired. The white can be re-identified as black with black tape or equivalent and then used as a hot wire. > it's at the same potential as you are. Both are grounded to the earth and > (hopefully) there is no potential difference when a person contacts the > white wire; threrefor no shock hazzard (under normal conditions, IE wired > properly in the first place.) The difference is that the neutral (groundED) wire carries current, under normal circumstances. The groundING wire does not. It takes two faults to shock/hurt/kill you if you are in contact with the grounding wire; it takes one fault to shock/hurt/kill you if you are in contact with the neutral wire. Ed In alt.engineering.electrical ehsjr <ehsjr@bellatlantic.net> wrote: |>>I have been told, but have never sacrificed a device to verify, or set up |>>the appropriate test, that GFCI receptacles open BOTH the hot wire AND the [quoted text clipped - 8 lines] | Both the neutral and the hot are interrupted when | a GFCI receptacle trips. So why is the neutral opened? That's an "academic question" (I can come up with what I think are good reasons to do so). Now, considering answers to this question, what protections might be lost if AFCI breakers that include GFCI protection at the 5ma level result in GFCI receptacles not being used? Is GFCI protection in a breaker considered adequate for the requirements in NEC 210.8 even though it does not open the neutral connection? Would YOU persoanlly feel less safe if all the receptacles in a kitchen were protected for ground fault leakage only by circuit breakers at the panel (assume that the panel is close by). There must be _some_ reason _they_ chose to include opening the neutral in GFCI receptacles (maybe more than one). But wouldn't such reasons also be applicable to circuit breaker based protection? What if you have _both_ GFCI protection at the breaker _and_ GFCI protection at the receptacle, say in a bathroom. Now suppose there is a slight leakage fault, but only the breaker opens on it. Maybe the receptacle was going to interrupt the fault, but was just sufficiently slow, perhaps due to a slow rise in the leakage current, that the breaker did it first, which prevents the receptacle from doing so. Now you have a condition where the neutral continues to be fully connected all the way from the main panel, through the GFCI receptacle that no longer has power on it's hot wire, and into the plugged in appliance that someone grabbed with a dripping wet hand while also grabbing a towel out of the basin water in the sink. Well, usually, a neutral doesn't have much voltage relative to ground. But if there was some kind of open neutral condition also present (now we are at the level of _two_ existant problems) and a rather unbalanced load between the two single phase poles (somewhat common), we could be dealing quite many volts still available through the GFCI receptacle that didn't trip because it lost power due to the ground fault that was detected by the breaker first. So my thinking here is, if there is protection to be gained by opening the neutral at GFCI receptacles, we should _not_ be requiring that AFCI breakers be of the type that combine GFCI protection. And perhaps such breakers should be prohibited for these circuits. Of course there is also the issue of the inconvenience of going all the way to the breaker panel to reset a ground fault. This could be particularly so for bathrooms (imagine being dripping wet, wearing only a towel, going out to the garage or down to the basement, standing on a concrete floor, to reset a breaker). |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-10-01-0450@ipal.net | |------------------------------------/-------------------------------------| > In alt.engineering.electrical ehsjr <ehsjr@bellatlantic.net> wrote: > |>>I have been told, but have never sacrificed a device to verify, or set up [quoted text clipped - 52 lines] > out to the garage or down to the basement, standing on a concrete floor, > to reset a breaker). What makes you so certain that a GFCI circuit breaker does not open the neutral? Have you checked with several manufacturers. One reason why it might be OK for a breaker to leave the neutral alone is that it is far less likely and in fact rather difficult for a breaker to be revere wired. When a breaker type GFCI operates it will nearly always open the ungrounded conductor. There are a lot more ways a receptacle type of GFCI can be supplied with the ungrounded conductor controlled by the grounded conductor leg of the GFCI mechanism. SignatureTom Horne "This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison In alt.engineering.electrical Member, Takoma Park Volunteer Fire Department <postmaster@takomaparkfire.org> wrote: | What makes you so certain that a GFCI circuit breaker does not open the | neutral? Have you checked with several manufacturers. I've looked at the engineering diagrams, cut-aways, and schematics. There are no contacts for interrupting the neutral wire. | One reason why it might be OK for a breaker to leave the neutral alone | is that it is far less likely and in fact rather difficult for a breaker | to be revere wired. When a breaker type GFCI operates it will nearly | always open the ungrounded conductor. There are a lot more ways a | receptacle type of GFCI can be supplied with the ungrounded conductor | controlled by the grounded conductor leg of the GFCI mechanism. So basically, there is no goal or interest in specifically opening the neutral. It's just a case of opening both in situations where either might be the neutral. |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / spamtrap-2006-10-02-0306@ipal.net | |------------------------------------/-------------------------------------| >>the way a GFCI functions, would it trip >>if a bad connection were made to it ? [quoted text clipped - 7 lines] >I don't think so. Why would the resistance of a bad connection be any >different from the resistance of a light bulb. Let me say what I said another way. GFCI outlets and circuit breakers measure if there is a difference between the amount of current going throught the hot wire and though the neutral wire. If they are the same, the gfci sees no problem. Having a loose connection does not mean that will happen. Using an appliance that shorts to your body and from there to some other path than the neutral wire *would* cause it to trip. OTOH, if you took two all-metal screwdrivers, one in each hand, and stuck one into each of the slots in an outlett, even a GFCI outlet, you could burn your heart to a fine grey ash, and the breaker would not trip. Because the same amount of current was going through the two conductors. >I wouldn't assume there will be arcing just because a connection isn't >tight enough. So I wouldn't assume that even an arc fault circuit >breaker would be tripped by a loose connection. Am I right or wrong? > the way a GFCI functions, would it trip > if a bad connection were made to it ? [quoted text clipped - 4 lines] > the terminal to warm up - would the > GFCI trip ?) There's all kinds of "bad connections". If the bad connection resulted in a difference of 5 mA or more between the current in the neutral versus the current in the hot wire, the GFCI would trip. The example you gave would not cause the GFCI to trip. Ed As others have mentioned, a GFCI would probably not trip. They sense current differences, and usually have current overload sensing in them also. But a bad connection causing the terminal to warm up would not trip it unless it got very hot, and even then the results are indeterminate. > the way a GFCI functions, would it trip > if a bad connection were made to it ? [quoted text clipped - 4 lines] > the terminal to warm up - would the > GFCI trip ?) > the way a GFCI functions, would it trip > if a bad connection were made to it ? [quoted text clipped - 4 lines] > the terminal to warm up - would the > GFCI trip ?) So far there has been a lot of misinformation in replies to this thread. Only the smoke will indicate a simple HOT connection. If there is any arcing a AFCI should detect the fault and disconnect. Quote "The “AFCI” is an arc fault circuit interrupter. AFCIs are newly-developed electrical devices designed to protect against fires caused by arcing faults in the home electrical wiring." **** A GFCI will only protect from differences in the current flowing in the two conductors beyond the GFCI. It will cutoff the current when a very small current difference, 5 or 30 ma., is detected and should do it quick enough to save a person from electrocution. Neither device is intended to protect from voltage spikes and neither device can detect a simple hot connection. A hot connection alone will not csause a difference in current between the 2 legs of the circuit, only a ground fault can cause that and a GFCI should detect that. SignatureJohn G Wot's Your Real Problem? |
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