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GFCI operation question

Discussion in 'Electrical Engineering' started by Methos, Aug 25, 2006.

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  1. Guest

    | In article <>,
    | writes:
    |>| In article <[email protected]>,
    |>|> 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.
    |
    | 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
    | 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.

    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.
     
  2. daestrom

    daestrom Guest

    That will raise the groundED conductor potential, yes. But that alone won't
    trip the GFCI, would also need a groundED-groundING fault downstream of the
    GFCI. And *that* sort of fault will trip it right away, regardless of a
    sub-panel issue or not (because of the 'signal' injected into the groundED
    conductor by the GFCI itself).
    May be. Old GFCI's didn't have the extra circuit to inject this signal, but
    newer ones do (think it was a code change that added it).

    daestrom
     
  3. daestrom

    daestrom Guest

    Yes, the ones I have seen it's nothing more than a toroid core that the
    'hot' and 'neutral' pass through, with a few turns of a second 'winding'
    that is fed from hot and neutral 'upstream' of both this toroid and the
    sensor one. Perhaps a resistor in series with this 'primary winding', can't
    remember now. The winding is fed from 'across the line', and the 'output'
    is a common-mode signal on groundED and ungrounded current carrying
    conductors.

    daestrom
     
  4. Guest

    |
    | |> On Thu, 05 Oct 2006 00:10:16 GMT daestrom
    |>
    |> | Don't see what your thinking there. If the groundED conductor has no
    |> load
    |> | on it, then it's at the same potential at the GFCI as it is in the
    |> service
    |> | panel. Ditto for the groundING conductor, so there is no current flow
    |> | through a groundED - groundING conductor fault downstream of the GFCI.
    |>
    |> If the groundED conductor splits off somewhere between the point it is
    |> bonded to ground, and where the GFCI is, then a load on another circuit
    |> at that point can create the voltage drop on the feeder to that point,
    |> and give you the voltage. Think of a subpanel.
    |>
    |
    | That will raise the groundED conductor potential, yes. But that alone won't
    | trip the GFCI, would also need a groundED-groundING fault downstream of the
    | GFCI. And *that* sort of fault will trip it right away, regardless of a
    | sub-panel issue or not (because of the 'signal' injected into the groundED
    | conductor by the GFCI itself).

    But what if the fault downstream is not a solid fault, but a person
    contacting the neutral wire.

    What it comes down to, is I want GFCI protection that always opens
    both wires. And I want it to work even if AFCI in installed. My
    easier posting (maybe not in this thread) described how GFCI could
    fail with combination AFCI installed, leaving this vulnerability.

    1.

    The combination AFCI+GFCI might trip on the fault first, leaving the
    downstream GFCI unpowered to do its thing, leaving the neutral in a
    connected state, with a reduced but non-zero hazard being present.

    2.

    The fault on the neutral might cause GFCI tripping to operate in a
    continuous manner, potentially burning out the GFCI solenoid. That
    process could get worse.

    I'm not yet convinced that combining GFCI protection in AFCI is such
    a good thing. There is the neutral issue, as well as the residual
    charging current issue (for long branch circuits). If the load is
    far from the service entrance, you either run a long branch and have
    the excess charging current diminish the GFCI range and increase the
    nuisance trips, or you use a subpanel and raise the neutral voltage
    above the bonding point, or you have the expensive of "one circuit"
    subpanels for each place that has special risk for GFCI (wet places),
    or use a transformer with a newly derived neutral bonded to the feeder
    grounding wire.

    If you think a neutral wire is safe, then I'll let you be the one to
    try it. Stand barefoot on a wet concrete floor at ground level, and
    lick a bare neutral wire with your tongue :) I certainly would not
    ever do that.


    |> I wonder if this is the cause of being able to dangerously trip GFCI
    |> receptacles with a radio transmitter.
    |>
    |
    | May be. Old GFCI's didn't have the extra circuit to inject this signal, but
    | newer ones do (think it was a code change that added it).

    So maybe it is the newer GFCIs that are vulnerable to the radio because
    of their circuit that checks this injected signal?
     
  5. On top of that, consider open neutral events.
    How many electricians have been injured or died from miswired milti-wire
    branch circuits?
    How many homes have had devices wiped out from open neutral between the
    transformer and main panel?
     
  6. Guest

    |
    | |
    |> If you think a neutral wire is safe, then I'll let you be the one to
    |> try it. Stand barefoot on a wet concrete floor at ground level, and
    |> lick a bare neutral wire with your tongue :) I certainly would not
    |> ever do that.
    |>
    |
    | On top of that, consider open neutral events.
    | How many electricians have been injured or died from miswired milti-wire
    | branch circuits?
    | How many homes have had devices wiped out from open neutral between the
    | transformer and main panel?

    I've seen 2 open neutral events in homes. I lived in one, and we were
    lucky enough to not lose anything except the evening dinner. My mother
    thought it was funny that the light over the bar opening would go up and
    down in brightness as she turned burners on the stove on and changed
    their setting. I was 14 at the time, but I knew what an open neutral
    could do and immediately recognized it. Turns out that light had been
    tapped from the stove circuit, and was the only thing like that. But
    it got some other wiring issues in the house fixed up in a hurry, like
    the open split bolt splice hanging on nails on a wooden board that fed
    the stove. At first I thought that was where the neutral was open.
    But as it turns out, it was open in the fuse box. But the electrician
    got it all cleaned up that day, finally. The other even I saw was in
    a neighbor's house. I never found out where it was caused from, but
    she did complain to my dad that the clock built in to her stove had
    quit working and was smoking. We got her disconnected, but she did
    have to get a new stove as a result.
     
  7. John Gilmer

    John Gilmer Guest

    ASSuming they are qualified and have a little experience, I would think the
    answer would be damn few.


    Likely, quite a few. It's happen to me. But as far as I could determine
    I didn't lose anything important. Some of the expensive stuff seems to be
    pretty resistant to over voltage damage (computer power supplies and
    electronics) or has thermally protected motors or whatever. Most of the
    interior lamps are CFs but in any case I didn't find a large numbr of burned
    out lamps of any type.
     
  8. Even among the experienced, there is still the risk of miswired circuits.
    Even measuring the current before opening the neutral can fail if the load
    is intermittent, like a water cooler or other thermostatic controlled
    device.
    If it gets anywhere near the full 240V possible, not many consumer
    electronic devices can take that.
     
  9. Guest

    | If it gets anywhere near the full 240V possible, not many consumer
    | electronic devices can take that.

    OTOH, autoranging switch mode power supplies seem to have no trouble.
    the just have short switch-on times for the higher voltage, up to the
    voltage they are rated for breakdown, which for international units is
    going to be at least 250 volts as found in China. There may even be
    a chance they can work on 277 volts in the USA (though not officially
    rated at such because who would ever need to do that).

    I have heard that some of the switch mode supplies that have the switch
    to change between voltages (usually marked as 110/220 or 115/230) are
    not really change a transformer between series and parallel, but rather
    are just changing some component values in the circuitry to operate
    better at the selected voltage (maybe to reduce harmonics or improve
    the power factor at that voltage).

    The more such power supplies we can encourage electronics and appliance
    manufacturers to use, provided the harmonics and power factor issues are
    not a problem, the better off we are.
     
  10. More than one IT equipment manufacterer has started to produce special
    supplies for China / India.
    Those supplies will work on US 277 V. Off label, but within specs for most
    of them.
    I don't think any of the "special" ratings are published.

    Yep, autorangers have no problem. I have used them on 240V or 480V with a
    control power stepdown to 120V because it gives such a good margin for
    overvotlage - double input is OK

    Autorangers are common on laptops, cell phone chargers, battery chargers, or
    other devices that may be used internationally. They tend to be in the
    lower power rated supplies.

    120/240 supplies switch the rectifier type depending on input voltge. In
    the 240V position, they are a full wave rectifier. In the 120V position
    they are configured as voltage doublers. Either way, the bus voltage is
    supposed to be around 280V to 350V. In the 120V position, 240V will take
    them out. Most PC supplies are this type. Some are autoswitching, but a
    sudden increase from 120V while operating can take them out.

    Consumer electronics are often 120V only. This is because their high volume
    and NA unique requirements (NTSC, ATSC, frequency alocation) make it cost
    effective to use 120V only supplies. With these also, 240V will wipe them
    out.
     
  11. John Gilmer

    John Gilmer Guest

    Quite possible. But if you are just living "normally" when the neutral
    goes out you end up with some light VERY bright and some very dim.

    And, from my experience, the dropped neutral (from the service drop) doesn't
    take out much (if anything).

    Of course, when the service drop neutral goes there is still the earth path
    between the power company ground (which "around here" is said to be 'zero
    ohms') and whatever ground that is bonded to neutral in the panel and meter
    base.

    Another thing I had going for me is that I have a metalic connection from my
    deep well right up through my water tank to the household grounding wires.
    If you included the water heater ground there is the equivalent of a #10
    wire between the well metalics and the panel ground. The negative is that
    the power company ground is 400' away from my meter box.

    More urban folks may not have such a good house ground and urban low voltage
    distribution may not ground as effective as the rural providers do.

    When in comes to a three wire 240/120 load circuit, of course, a lifted
    neutral might, for example, power a TV set and a toaster. When the neutral
    goes the TV would likely see no voltage. When someone decides to use the
    toaster the TV may become toast!
     
  12. Guest

    | 120/240 supplies switch the rectifier type depending on input voltge. In
    | the 240V position, they are a full wave rectifier. In the 120V position
    | they are configured as voltage doublers. Either way, the bus voltage is
    | supposed to be around 280V to 350V. In the 120V position, 240V will take
    | them out. Most PC supplies are this type. Some are autoswitching, but a
    | sudden increase from 120V while operating can take them out.

    But autoswitching is NOT the same as autoranging, correct?

    So the autoswitchers are best switched only from a power coming on state?

    Can the autorangers function for any voltage in between 120 and 240?

    The impression I got from the designs I saw for a switch mode power supply,
    which was not really complete info, is that on a higher voltage the time
    the current flowed was shorter, and for a lower voltage it was longer.
    But maybe that was just for some brownout handling. I have seem power go
    completely out for an instant, long enough for the lights to go all the
    way out and even for clocks to lose time, and yet, my computers stayed up.
    I guess the capacitors have enough reserve and I'm not loading them up on
    the DC side too much.


    | Consumer electronics are often 120V only. This is because their high volume
    | and NA unique requirements (NTSC, ATSC, frequency alocation) make it cost
    | effective to use 120V only supplies. With these also, 240V will wipe them
    | out.

    As long as a single voltage supply has a cost lower than a dual voltage
    by an amount greater than the savings of having only one type of supply
    being manufactured and in inventory, then I guess we wil continue to see
    them, and have damages.

    So why are PC supplies pretty much all dual voltage or autoranging? I can
    see that for laptop external power converters, as they may be used in some
    other country. But for towers that don't move around much?
     
  13. Autoswitching and autoranging usually mean the same thing.

    Wide range is the term you are looking for.
    Wide range can.

    One place where autorange or manual switched 120 /240 designs can get into
    trouble is 208V feed. The supplies that include 90V for Japan are OK.
    Supplies for 120V or 240V only with a lower limit of 102V/204V get into
    trouble becuase there is not enough margin on 208V.
    Wide range supplies under 90W will have just a straight rectifier on the
    input. When supplied with 240V, they have a large ride through because the
    ride through is based on minimum voltage. At 2.5 X the minimum input, the
    cap has 6.25 times as much energy.

    Over 90W, and the supplies have power factor correction. They boost the AC
    to 380V DC, regardless of input voltage. This makes them invariant of input
    voltage for ride though time.
    One PC design can be shipped to anywhere in the world, with the only change
    being the power cord, keyboard, manual, software, and shipping carton. The
    tower doesn't change. So it makes sense to have a power supply that will
    work anywhere in the world.

    Consumer electronics are either NA or ROW because of NTSC,ATSC,PAL,SECAM &
    frequency allocation. Here the box itself is specific to end user location,
    so a unique supply is cheaper.
     
  14. Guest

    |
    | |>
    |> | 120/240 supplies switch the rectifier type depending on input voltge.
    |> In
    |> | the 240V position, they are a full wave rectifier. In the 120V position
    |> | they are configured as voltage doublers. Either way, the bus voltage is
    |> | supposed to be around 280V to 350V. In the 120V position, 240V will
    |> take
    |> | them out. Most PC supplies are this type. Some are autoswitching, but
    |> a
    |> | sudden increase from 120V while operating can take them out.
    |>
    |> But autoswitching is NOT the same as autoranging, correct?
    |>
    |> So the autoswitchers are best switched only from a power coming on state?
    |
    | Autoswitching and autoranging usually mean the same thing.
    |
    | Wide range is the term you are looking for.

    The specifications of some power supplies say 100-250 volts. So shouldn't
    that mean they could operate just fine on 150 volts? These say autoranging.


    |> Can the autorangers function for any voltage in between 120 and 240?
    |
    | Wide range can.

    So are the makers like Antec just trying to pull a fast one on people?


    | One place where autorange or manual switched 120 /240 designs can get into
    | trouble is 208V feed. The supplies that include 90V for Japan are OK.
    | Supplies for 120V or 240V only with a lower limit of 102V/204V get into
    | trouble becuase there is not enough margin on 208V.

    So what is the term to look for on the power supplies to get the right ones?
    And which manufacturers make them?

    How would you select a power supply for a PC if you needed to connect them
    to a 208 volt power source? I assume if it were a 240 volt power source
    (e.g. single phase in the USA, L-L) you wouldn't have any trouble.


    |> The impression I got from the designs I saw for a switch mode power
    |> supply,
    |> which was not really complete info, is that on a higher voltage the time
    |> the current flowed was shorter, and for a lower voltage it was longer.
    |> But maybe that was just for some brownout handling. I have seem power go
    |> completely out for an instant, long enough for the lights to go all the
    |> way out and even for clocks to lose time, and yet, my computers stayed up.
    |> I guess the capacitors have enough reserve and I'm not loading them up on
    |> the DC side too much.
    |
    | Wide range supplies under 90W will have just a straight rectifier on the
    | input. When supplied with 240V, they have a large ride through because the
    | ride through is based on minimum voltage. At 2.5 X the minimum input, the
    | cap has 6.25 times as much energy.
    |
    | Over 90W, and the supplies have power factor correction. They boost the AC
    | to 380V DC, regardless of input voltage. This makes them invariant of input
    | voltage for ride though time.

    How do they boost the AC voltage regardless of input? Sounds like a nice
    trick a lot of things might like to do.

    What do you mean by "ride though time"? Does that imply or mean there is
    a time limit?


    |> | Consumer electronics are often 120V only. This is because their high
    |> volume
    |> | and NA unique requirements (NTSC, ATSC, frequency alocation) make it
    |> cost
    |> | effective to use 120V only supplies. With these also, 240V will wipe
    |> them
    |> | out.
    |>
    |> As long as a single voltage supply has a cost lower than a dual voltage
    |> by an amount greater than the savings of having only one type of supply
    |> being manufactured and in inventory, then I guess we wil continue to see
    |> them, and have damages.
    |>
    |> So why are PC supplies pretty much all dual voltage or autoranging? I can
    |> see that for laptop external power converters, as they may be used in some
    |> other country. But for towers that don't move around much?
    |
    | One PC design can be shipped to anywhere in the world, with the only change
    | being the power cord, keyboard, manual, software, and shipping carton. The
    | tower doesn't change. So it makes sense to have a power supply that will
    | work anywhere in the world.
    |
    | Consumer electronics are either NA or ROW because of NTSC,ATSC,PAL,SECAM &
    | frequency allocation. Here the box itself is specific to end user location,
    | so a unique supply is cheaper.

    But the power supply is still a component. They either have to stock two
    different power supplies, or one, at the place where the whole electronics
    is manufactured. Why is it cheaper to have only one power supply design
    for computers but not so for TV sets?
     

  15. Another term used is universal range - I was grasping for the other term
    earlier and didn't remember until now.

    If it's not speced as 2 descrete ranges, then it's likely wide range /
    universal range and should work anywhere in the whole range.
    I think it may be a case of marketing types writing the spec sheet.

    PC's are usually OK. They are designed for 90-140 on the low range and
    180-280 on the high range.
    180V is plenty of margin on a 208V supply.

    The equipment I had trouble with were industrial power supplies.
    Look Here:
    http://focus.ti.com/analog/docs/techdocsabstract.tsp?familyId=662&abstractName=slua144
    http://tinyurl.com/q22gh

    TI is trying to sell the chip so it's written towards that aim, but it is
    one of the better (free) articles on PFC design.
    Yep.

    Look here:
    http://www.powerstandards.com/itic.jpg

    That is the current CBEMA standard. It once was 8.3ms. Way to many crashes
    from dips, so now it's 20ms.
    Often the entire product design is a ROW of NA only, so there really isn't a
    case of two power supplies.
     
  16. Guest

    | Another term used is universal range - I was grasping for the other term
    | earlier and didn't remember until now.
    |
    | If it's not speced as 2 descrete ranges, then it's likely wide range /
    | universal range and should work anywhere in the whole range.

    I've seen them spec'd at "100-250", presumably the lowest (Japan) and
    highest (China) nominal home/office building distribution voltages.
    Hopefully there is some undervoltage and overvoltage margin in that.


    |> |> Can the autorangers function for any voltage in between 120 and 240?
    |> |
    |> | Wide range can.
    |>
    |> So are the makers like Antec just trying to pull a fast one on people?
    |
    | I think it may be a case of marketing types writing the spec sheet.

    Now there's an area where we could use some government intrusion and
    require some licensing. As it is now we have to depend on land sharks.


    |> | One place where autorange or manual switched 120 /240 designs can get
    |> into
    |> | trouble is 208V feed. The supplies that include 90V for Japan are OK.
    |> | Supplies for 120V or 240V only with a lower limit of 102V/204V get into
    |> | trouble becuase there is not enough margin on 208V.
    |>
    |> So what is the term to look for on the power supplies to get the right
    |> ones?
    |> And which manufacturers make them?
    |>
    |> How would you select a power supply for a PC if you needed to connect them
    |> to a 208 volt power source? I assume if it were a 240 volt power source
    |> (e.g. single phase in the USA, L-L) you wouldn't have any trouble.
    |
    | PC's are usually OK. They are designed for 90-140 on the low range and
    | 180-280 on the high range.
    | 180V is plenty of margin on a 208V supply.
    |
    | The equipment I had trouble with were industrial power supplies.

    The old "some places have 240 and some places have 208" for single phase
    supply (and even three phase) is a big annoyance sometimes.


    |> How do they boost the AC voltage regardless of input? Sounds like a nice
    |> trick a lot of things might like to do.
    |
    | Look Here:
    | http://focus.ti.com/analog/docs/techdocsabstract.tsp?familyId=662&abstractName=slua144
    | http://tinyurl.com/q22gh
    |
    | TI is trying to sell the chip so it's written towards that aim, but it is
    | one of the better (free) articles on PFC design.

    Could this chip be used to control a device that regulates the AC voltage
    (AC in, AC out) for a building on the order of 200 amps or more?


    |> What do you mean by "ride though time"? Does that imply or mean there is
    |> a time limit?
    |
    | Yep.
    |
    | Look here:
    | http://www.powerstandards.com/itic.jpg
    |
    | That is the current CBEMA standard. It once was 8.3ms. Way to many crashes
    | from dips, so now it's 20ms.

    OK, 5 cycles to 12 cycles in 60 Hz systems.

    I've seen a PC stay up in around 400 to 500 millisecond outage. I saw an
    old Apple II (circa late 1970's) stay up in a 1.5 second long outage.


    |> But the power supply is still a component. They either have to stock two
    |> different power supplies, or one, at the place where the whole electronics
    |> is manufactured. Why is it cheaper to have only one power supply design
    |> for computers but not so for TV sets?
    |>
    |
    | Often the entire product design is a ROW of NA only, so there really isn't a
    | case of two power supplies.

    If the power supplies are built on the same floor as the end product, then
    I can see that being the case. But if the power supplies are sourced in,
    then I believe there would be economic advantage to have one model instead
    of two.

    And if we start seeing single DC output voltage designs for PCs in the
    next generation of PC architecture, I think that will help to bring P/S
    costs even further down.
     
  17. Ben Miller

    Ben Miller Guest

    All GFCIs today must detect a NG connection downstream, regardless of
    whether or not a load is connected. They inject current on BOTH the hot &
    neutral so things stay balanced with any load, as long as there is no
    additional return path that bypasses the neutral.

    Ben Miller
     
  18. Ben Miller

    Ben Miller Guest

    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
     
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