hazards of GFCI and AFCI protection devices

In another thread, the topic shifted from my original question
about GFCI and AFCI protection devices operating on undervoltage
circuits (such as a 120/60 2-pole circuit where a 2-pole breaker
would be seeing only 60 volts to ground), to oscillation faults
in GFCI (and possibly AFCI) protection device design.
I want to start a new thread so discussion can proceed under a
proper title.
The issue is that under some conditions, such as operation at half
voltage, or when non-supply sources of fault detection take place
(such as an RF field), the devices can go into oscillation, trying
to continuously open the a circuit, either unsuccessfully (as in
the undervoltage case), or successfully (as in the non-supply case),
and repeating that effort continuously with a solenoid probably
rated only for momentary and infrequent duty cycles. Continuous
operation could overheat the solenoid with the possible risk of
causing a short circuit in the device (which is still attached to
a source of power) and possibly causing a fire in the building,
and injury or death to persons in the building (possibly asleep).
An example of an undervoltage condition that can exist is when a
utility transmission or distribution transformer with a three phase
delta configuration primary (the most common) loses one of the three
hot phase lines, then two of the secondary windings (usually in a
wye or star configuation) will be energized with only half voltage
due to their primary windings being in series with the remaining
two phases (effectively a one phase voltage). I'm told that this
condition is supposed to be detected and the entire circuit shut out
when it happens to prevent damage. I can't say how many times it
actually works correctly because I don't know if this is even the
cause in outages I have experienced or known about. But I have
experienced cases where the condition occurs and does not result
in complete opening of all the phases. In one case, the condition
existed for over 3 hours. I have also been told by 2 different
people of other cases. One is a case that lasted over 24 hours.
Another is a case of involving a 765kV transmission line with one
phase down to ground and remaining energized for over 45 minutes
(and presumably the other 2 phases energized which would create
the single phasing condition at the destination of that line.
In my opinion, the cases are sufficiently often that certain
protection devices should ideally continue to function correctly,
or at a very minimum not contribute further to hazards.
Undervoltage certainly presents many hazards, such as stalled motors
that burn up. But for now I want to focus on the GFCI/AFCI risks.
A GFCI/AFCI device designed to operate correctly, or at least lock
itself out from operation in certain cases, over a voltage range of
40% to 125%, would eliminate or reduce one risk source. Filtering
and shielding of RF energy from falsely tripping the device, or at
least locking out the tripping mechanism once tripped, would reduce
the other risk source.
Under a sufficiently strong RF field, a GFCI/AFCI device could be
tripped. But because the device remains energized from the supply
side, and the current differential detection circuitry continues to
operate after opening the main circuit contacts, it can repeat the
tripping action indefinitely. These devices are normally designed
under the assumption that once the power source is removed from the
faulty load, no further ground fault current will be present and
whether the detection circuitry is still active or not is supposedly
moot (but not really in the RF field case).
My goal is to have these devices improved so that they function in a
non-hazardous way over a supply voltage that between 40% and 125% of
the nominal voltage, and/or under an RF field equivalent to 10 watts
of power within 1 meter from a half wave radiator (antenna). There
are two ways to deal with the RF problem. One is to filter the RF
out of the device so it does not falsely trip under these conditions.
The other is to design in a mechanism or circuit so that a false trip
that cannot be cleared by opening the power contacts will not cause
continous tripping or solenoid oscillation.
Possible directions to pursue include working with the NFPA (to add
requirements in the NEC that its GFCI/AFCI requirements are only met
by devices that meet these improved guidelines) and Underwriters
Laboratory (to require devices meet these improved guidelines to be
listed). I doubt the pursuit can go through manufacturers since
they are unlikely to want to add costly design improvements unless
all their competitors are doing under equal requirements. However,
some manufacturers may be willing to help push the agenda at the
level of NEC and/or U/L requirements.
I know of no injuries or deaths as a result of this hazard. However
I am also a believer that we should not wait for an injury or death
to proceed with efforts to eliminate or reduce the hazard when we
can understand the hazard exists.
Reply to
phil-news-nospam
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I want to see some independent statistics showing me how many people die under this type of N-x situation, before I am going to spend more of my money on this protection than I already do.
I also want some guarantee that in 2 to 3 years, no-one is going to be able to envision a set of circumstances under which your dream protection dose not provide protection to every user in the world.
Because if you cannot guarantee me better protection than we now have, you can just go pound sand. For you are nothing more than a fear monger trying to line your own pockets at my expense - through a legislated (read: Guaranteed Income) solution to yet another problem which does not exist.
HR.
Reply to
Rowbotth
| I want to see some independent statistics showing me how many people die | under this type of N-x situation, before I am going to spend more of my | money on this protection than I already do.
So you are one of those people that insist that people die first, before doing something to correct a problem before someone dies. I will suggest that when the first person dies that they sue you for their loss because you wanted someone to die first.
| I also want some guarantee that in 2 to 3 years, no-one is going to be | able to envision a set of circumstances under which your dream | protection dose not provide protection to every user in the world.
I don't know what you mean by that.
| Because if you cannot guarantee me better protection than we now have, | you can just go pound sand. For you are nothing more than a fear monger | trying to line your own pockets at my expense - through a legislated | (read: Guaranteed Income) solution to yet another problem which does | not exist.
This is not lining my pockets at all. I will gain nothing financially by it. In fact I will end up having to pay more for the protection just like everyone else. I just to want to have to keep paying a lot for what I have found to be cheap garbage that puts me and my family at risk.
Reply to
phil-news-nospam
The original inventor of the Arc Fault Circuit Interrupter has an excellent site on the subject at:
formatting link

> In another thread, the topic shifted from my original question > about GFCI and AFCI protection devices operating on undervoltage > circuits (such as a 120/60 2-pole circuit where a 2-pole breaker > would be seeing only 60 volts to ground), to oscillation faults > in GFCI (and possibly AFCI) protection device design. > > I want to start a new thread so discussion can proceed under a > proper title. > > The issue is that under some conditions, such as operation at half > voltage, or when non-supply sources of fault detection take place > (such as an RF field), the devices can go into oscillation, trying > to continuously open the a circuit, either unsuccessfully (as in > the undervoltage case), or successfully (as in the non-supply case), > and repeating that effort continuously with a solenoid probably > rated only for momentary and infrequent duty cycles. Continuous > operation could overheat the solenoid with the possible risk of > causing a short circuit in the device (which is still attached to > a source of power) and possibly causing a fire in the building, > and injury or death to persons in the building (possibly asleep). > > An example of an undervoltage condition that can exist is when a > utility transmission or distribution transformer with a three phase > delta configuration primary (the most common) loses one of the three > hot phase lines, then two of the secondary windings (usually in a > wye or star configuation) will be energized with only half voltage > due to their primary windings being in series with the remaining > two phases (effectively a one phase voltage). I'm told that this > condition is supposed to be detected and the entire circuit shut out > when it happens to prevent damage. I can't say how many times it > actually works correctly because I don't know if this is even the > cause in outages I have experienced or known about. But I have > experienced cases where the condition occurs and does not result > in complete opening of all the phases. In one case, the condition > existed for over 3 hours. I have also been told by 2 different > people of other cases. One is a case that lasted over 24 hours. > Another is a case of involving a 765kV transmission line with one > phase down to ground and remaining energized for over 45 minutes > (and presumably the other 2 phases energized which would create > the single phasing condition at the destination of that line. > In my opinion, the cases are sufficiently often that certain > protection devices should ideally continue to function correctly, > or at a very minimum not contribute further to hazards. > > Undervoltage certainly presents many hazards, such as stalled motors > that burn up. But for now I want to focus on the GFCI/AFCI risks. > > A GFCI/AFCI device designed to operate correctly, or at least lock > itself out from operation in certain cases, over a voltage range of > 40% to 125%, would eliminate or reduce one risk source. Filtering > and shielding of RF energy from falsely tripping the device, or at > least locking out the tripping mechanism once tripped, would reduce > the other risk source. > > Under a sufficiently strong RF field, a GFCI/AFCI device could be > tripped. But because the device remains energized from the supply > side, and the current differential detection circuitry continues to > operate after opening the main circuit contacts, it can repeat the > tripping action indefinitely. These devices are normally designed > under the assumption that once the power source is removed from the > faulty load, no further ground fault current will be present and > whether the detection circuitry is still active or not is supposedly > moot (but not really in the RF field case). > > My goal is to have these devices improved so that they function in a > non-hazardous way over a supply voltage that between 40% and 125% of > the nominal voltage, and/or under an RF field equivalent to 10 watts > of power within 1 meter from a half wave radiator (antenna). There > are two ways to deal with the RF problem. One is to filter the RF > out of the device so it does not falsely trip under these conditions. > The other is to design in a mechanism or circuit so that a false trip > that cannot be cleared by opening the power contacts will not cause > continous tripping or solenoid oscillation. > > Possible directions to pursue include working with the NFPA (to add > requirements in the NEC that its GFCI/AFCI requirements are only met > by devices that meet these improved guidelines) and Underwriters > Laboratory (to require devices meet these improved guidelines to be > listed). I doubt the pursuit can go through manufacturers since > they are unlikely to want to add costly design improvements unless > all their competitors are doing under equal requirements. However, > some manufacturers may be willing to help push the agenda at the > level of NEC and/or U/L requirements. > > I know of no injuries or deaths as a result of this hazard. However > I am also a believer that we should not wait for an injury or death > to proceed with efforts to eliminate or reduce the hazard when we > can understand the hazard exists. > > -- > --------------------------------------------------------------------------
Reply to
Gerald Newton
| The original inventor of the Arc Fault Circuit Interrupter has an excellent | site on the subject at: |
formatting link
The page on that site with waveforms shows a computer waveform that has a duty cycle less than 1/3 the time. That would mean that my theory that neutral load dissipation due to computer switching power supply produced triplen current can easily exceed 300% of expected rating based on the average power used, if these computer loads represent 100% of all the load on the circuits with the shared neutral. Normal capacity increases of transformers, breaker panels, and special wiring bundles designed for extra neutral capacity is only 200%. While most uses won't exceed 200% due to a diversity of loads where computers do not exceed 1/3 of the total load, a small few could. The simple solution if 100% of your load is these switching power supplies is to get power using a transformer that has delta windings in both primary and secondary, and derate by 15%.
Reply to
phil-news-nospam
I read in sci.engr.electrical.compliance that snipped-for-privacy@ipal.net wrote (in ) about 'hazards of GFCI and AFCI protecti>
He means that if the devices were modified as you propose, that doesn't mean that someone else will find yet a further situation, however improbable, where the improved devices are unsatisfactory.
I didn't reply to you original post because it's far too long, and virtually unsnippable.
There are international standards covering the effects that concern you:
IEC 61008-2-2 and IEC 61009-2-2 on operation at reduced line voltage; IEC 61543 on electromagnetic compatibility (EMC).
EMC immunity has proved to be a problem with some designs, usually resulting in false tripping. There is an amendment to IEC 61543 at the first voting stage, but I don't know the content.
It may be that UL (or NFPA) has not adopted the above standards, in which case, maybe it should.
Reply to
John Woodgate
| He means that if the devices were modified as you propose, that doesn't | mean that someone else will find yet a further situation, however | improbable, where the improved devices are unsatisfactory.
That is possible. If they do find them, they should tell us about the issue so we understand it. It may be worthy.
Technology should never be stagnant.
| I didn't reply to you original post because it's far too long, and | virtually unsnippable.
Sorry. I just wanted to get the details out.
| There are international standards covering the effects that concern you: | | IEC 61008-2-2 and IEC 61009-2-2 on operation at reduced line voltage; | IEC 61543 on electromagnetic compatibility (EMC). | | EMC immunity has proved to be a problem with some designs, usually | resulting in false tripping. There is an amendment to IEC 61543 at the | first voting stage, but I don't know the content. | | It may be that UL (or NFPA) has not adopted the above standards, in | which case, maybe it should.
As long as the fix is not that hard to do, and I don't think it is, then it is something I think should be pursued.
If the solenoid can be spring activated, or some other mechanism or circuit employed to ensure it can complete the step of opening the circuit and locking it in the open position (where it can be reset) even though the electric supply to the solenoid is now off because the contacts are open, that should do the job.
Alternatively an added wire to the load side to tell the circuit that the contacts are indeed open, and prevent re-activation of the solenoid in such cases, would be another alternative.
I don't want to say what specific design must be used. I am primarily interested in some design being employed to prevent such activation.
Is the solenoid itself isolated in a fire-proof arc chamber? Maybe that is a way to deal with it (noisy but safer).
Reply to
phil-news-nospam

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