UPS wiring, hot/neutral/ground relationship

Discussion in 'Electrical Engineering' started by phil-news-nospam@ipal.net, Sep 20, 2006.

  1. Guest

    I am trying to find out some information about how 230 volt UPSes are
    wired up. In particular, I want to know how the output is wired with
    respect to the hot/neutral/ground wiring relationship. I am intending
    to get a "dual conversion continuous online" type of UPS, however, that
    may not actually happen, so I need to know this with respect to both
    types. I suspect the possibility these types may be different because
    the dual conversion type has more opportunity to isolate things.

    What I am looking for is knowledgeable information, not conjecture.
    I am do plenty of conjecturing, so that is not in short supply.

    I highly suspect, for safety and compliance reasons, the grounding wire
    is passed through solidly.

    It's the 2 power wires that I want to know about. There are three
    different kinds of systems in the world:

    1. A specific wire is always the grounded neutral wire, with outlets
    and plugs polarized to ensure the correct connection. This can be
    seen in countries like UK, Australia.

    2. One of the wires is the grounded neutral wire, but outlets and
    plugs are not polarized, so plugging in can result in either wire
    being the grounded one. This can be seen in countries like
    Germany.

    3. Neither of the wires is grounded. Each wire is at half voltage
    relative to ground, in opposing polarity so the different between
    them is the full voltage. Outlets and plugs may or may not
    be polarized, but this would not matter. This can be seen in
    countries like USA for 2 wire 240 volt circuits (e.g. what you
    might plug a heavy duty air conditioner into).

    I am wanting to operate the 230 volt UPS in the USA. What I want to
    be sure of is that there is no possibility of causing a short circuit
    through a backfeed, either in line interactive mode UPSes, or when
    a dual conversion UPS is in bypass mode.

    I believe that would only be possible if one of the output wires is
    grounded while both are being passed through electrically. Since that
    would pose a hazard in the German wiring, I suspect it would not be the
    case. But I cannot rule out there may be another wiring strategy that
    would be safe in both UK and Germany, but not safe with the USA wiring.

    A dual conversion UPS could be considered a "separate derived system"
    (in terms of electrical code), and probably wired as such. But how
    would it be grounded? I suspect one output wire is grounded and thus
    the other will be 230 volts relative to ground. If the switch that
    transfers to bypass mode is the "open transition" type, that should
    still be safe even with a USA power source, ehough it will result in
    a change in the voltages relative to ground when bypass in engaged.

    There are UPSes designed for higher voltage specifically in the USA,
    but these tend to be much larger capacity (over 3000 VA), specified
    for 208 volts (instead of 240 volts), and usually are three phase type.
    What I need is 1500 to 2500 VA single phase.

    I know most computer power supplies can be safely operated on 240 volts
    even with the USA style wiring. The power cutoff switch breaks both
    wires, and no assumption about which wire is made in any aspect of the
    power supply wiring. This is required in Germany due to the Schuko
    plug being able to rotate 180 degrees. I cannot recall ever seeing a
    computer power supply that cannot be operated on "220" (as labeled)
    either by means of a voltage change switch or autoranging.

    Still, the big question is how the output from the UPS is wired to,
    or otherwise made relative to, ground. These units don't generally
    use isolation transformers, so whatever is done, it is done as part
    of, or in conjunction with, the output DC/AC conversion circuit.

    Is there anyone using the "international" 230 volt UPSes on American
    style 240 volt (center tapped neutral) circuits?

    Do you see or have any reason to anticipate any safety issues?

    --
    |---------------------------------------/----------------------------------|
    | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
    | first name lower case at ipal.net / |
    |------------------------------------/-------------------------------------|
     
    , Sep 20, 2006
    #1
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  2. <> wrote in message
    news:...
    >I am trying to find out some information about how 230 volt UPSes are
    > wired up. In particular, I want to know how the output is wired with
    > respect to the hot/neutral/ground wiring relationship. I am intending
    > to get a "dual conversion continuous online" type of UPS, however, that
    > may not actually happen, so I need to know this with respect to both
    > types. I suspect the possibility these types may be different because
    > the dual conversion type has more opportunity to isolate things.
    >

    <snip>
    >
    > A dual conversion UPS could be considered a "separate derived system"
    > (in terms of electrical code), and probably wired as such.


    Actually no. Even dual conversion ups pass the neutral straight through so
    they are not separately derived sources.

    We test UPS for both US and European usage. If you connect a 240V UPS to a
    US style 240V supply, you can get large voltage swings from output line to
    ground when the UPS goes to battery. IMO, from our test results, the only
    safe way to use a 240 EU UPS on a US 240V supply is with an isolation
    transformer. The neutral connection of the UPS really needs to be the
    neutral and not a phase conductor.

    Remember, that even when the UPS is OFF, the neutral conductor WILL BE
    ENERGIZED if you connect it to a US 240V service.

    Charles Perry P.E.
     
    Charles Perry, Sep 20, 2006
    #2
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  3. Guest

    In alt.engineering.electrical Charles Perry <> wrote:
    |
    | <> wrote in message
    | news:...
    |>I am trying to find out some information about how 230 volt UPSes are
    |> wired up. In particular, I want to know how the output is wired with
    |> respect to the hot/neutral/ground wiring relationship. I am intending
    |> to get a "dual conversion continuous online" type of UPS, however, that
    |> may not actually happen, so I need to know this with respect to both
    |> types. I suspect the possibility these types may be different because
    |> the dual conversion type has more opportunity to isolate things.
    |>
    | <snip>
    |>
    |> A dual conversion UPS could be considered a "separate derived system"
    |> (in terms of electrical code), and probably wired as such.
    |
    | Actually no. Even dual conversion ups pass the neutral straight through so
    | they are not separately derived sources.

    The question is, how can they know which wire is the neutral? That is
    not identifiable when the incoming power uses a non-polarized plug such
    as the Schuko. Remember, the plug can be rotated 180 degrees. These
    would be UPSes generally designed for markets including Germany where
    L-N is 230 volts, but you don't know which line is neutral.

    Of course in my case I'd be using a NEMA-6-15 to C13 or to a C19. The
    output power would be to C13 outlets, and C14-C13 cords would be used
    to connect computers to it.


    | We test UPS for both US and European usage. If you connect a 240V UPS to a
    | US style 240V supply, you can get large voltage swings from output line to
    | ground when the UPS goes to battery. IMO, from our test results, the only
    | safe way to use a 240 EU UPS on a US 240V supply is with an isolation
    | transformer. The neutral connection of the UPS really needs to be the
    | neutral and not a phase conductor.

    When you say "goes to battery" I assume you mean a "line interactive UPS"
    as opposed to a "continuous dual conversion". I do expect a L-L voltage
    coming out in the 220-240 volt range. And I expect the hot wire coming
    out will be 220-240 volts relative ground when in conversion operation.
    So I realize I cannot depend on a lower L-G voltage as I might in a USA
    style wiring. OTOH, it's wrong to depend on the L-G voltage; only the
    L-N (or L-L if applicable) voltage should be considered.

    I presume these "international" power supplies are safe with either a
    "0-0-230" volt structure, or a "230-0-0" voltage structure, or a "115-0-115"
    voltage structure. Any reason to believe otherwise?

    When you say that an isolation transformer is needed, how are you expecting
    that transformer secondary to be wired? Would it be 100% floating? Or
    would one of the 2 wires (any center tapped not used to emulate EU power)
    be bonded to ground?


    | Remember, that even when the UPS is OFF, the neutral conductor WILL BE
    | ENERGIZED if you connect it to a US 240V service.

    Which conductor is the neutral conductor if you rotate the plug 180 degrees?

    You believe the off switch of such a UPS is single pole, not double pole?

    --
    |---------------------------------------/----------------------------------|
    | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
    | first name lower case at ipal.net / |
    |------------------------------------/-------------------------------------|
     
    , Sep 20, 2006
    #3
  4. <> wrote in message
    news:...
    > In alt.engineering.electrical Charles Perry <>
    > wrote:
    > |
    > | <> wrote in message
    > | news:...
    > |>I am trying to find out some information about how 230 volt UPSes are
    > |> wired up. In particular, I want to know how the output is wired with
    > |> respect to the hot/neutral/ground wiring relationship. I am intending
    > |> to get a "dual conversion continuous online" type of UPS, however, that
    > |> may not actually happen, so I need to know this with respect to both
    > |> types. I suspect the possibility these types may be different because
    > |> the dual conversion type has more opportunity to isolate things.
    > |>
    > | <snip>
    > |>
    > |> A dual conversion UPS could be considered a "separate derived system"
    > |> (in terms of electrical code), and probably wired as such.
    > |
    > | Actually no. Even dual conversion ups pass the neutral straight through
    > so
    > | they are not separately derived sources.
    >
    > The question is, how can they know which wire is the neutral? That is
    > not identifiable when the incoming power uses a non-polarized plug such
    > as the Schuko. Remember, the plug can be rotated 180 degrees. These
    > would be UPSes generally designed for markets including Germany where
    > L-N is 230 volts, but you don't know which line is neutral.
    >
    > Of course in my case I'd be using a NEMA-6-15 to C13 or to a C19. The
    > output power would be to C13 outlets, and C14-C13 cords would be used
    > to connect computers to it.
    >
    >
    > | We test UPS for both US and European usage. If you connect a 240V UPS
    > to a
    > | US style 240V supply, you can get large voltage swings from output line
    > to
    > | ground when the UPS goes to battery. IMO, from our test results, the
    > only
    > | safe way to use a 240 EU UPS on a US 240V supply is with an isolation
    > | transformer. The neutral connection of the UPS really needs to be the
    > | neutral and not a phase conductor.
    >
    > When you say "goes to battery" I assume you mean a "line interactive UPS"
    > as opposed to a "continuous dual conversion".


    No. A true double conversion UPS does not run on the battery at all times.
    The exact voltage at which it transfers to battery power depends on the
    manufacturer, model, and sometimes even settings.

    Another thing, don't think that a double conversion UPS will protect a load
    from all outages, voltage sags, or voltage swells. We find MANY units that
    will drop the load for certain input conditions that are not out of the
    ordinary.

    > I do expect a L-L voltage
    > coming out in the 220-240 volt range. And I expect the hot wire coming
    > out will be 220-240 volts relative ground when in conversion operation.
    > So I realize I cannot depend on a lower L-G voltage as I might in a USA
    > style wiring. OTOH, it's wrong to depend on the L-G voltage; only the
    > L-N (or L-L if applicable) voltage should be considered.
    >
    > I presume these "international" power supplies are safe with either a
    > "0-0-230" volt structure, or a "230-0-0" voltage structure, or a
    > "115-0-115"
    > voltage structure. Any reason to believe otherwise?
    >
    > When you say that an isolation transformer is needed, how are you
    > expecting
    > that transformer secondary to be wired? Would it be 100% floating? Or
    > would one of the 2 wires (any center tapped not used to emulate EU power)
    > be bonded to ground?
    >
    >
    > | Remember, that even when the UPS is OFF, the neutral conductor WILL BE
    > | ENERGIZED if you connect it to a US 240V service.
    >
    > Which conductor is the neutral conductor if you rotate the plug 180
    > degrees?
    >
    > You believe the off switch of such a UPS is single pole, not double pole?
    >


    A lot of what you ask depends on the size of UPS. We have done extensive
    testing on UPS that are 2kVA and larger. Most of these do not plug into a
    two pin Schuko, and they definitely have a terminal that is to be connected
    to neutral. I will have to ask one of my test engineers about the smaller
    units. I don't remember evaluating any.

    Charles Perry P.E.
     
    Charles Perry, Sep 20, 2006
    #4
  5. Guest

    In alt.engineering.electrical Charles Perry <> wrote:

    |> When you say "goes to battery" I assume you mean a "line interactive UPS"
    |> as opposed to a "continuous dual conversion".
    |
    | No. A true double conversion UPS does not run on the battery at all times.
    | The exact voltage at which it transfers to battery power depends on the
    | manufacturer, model, and sometimes even settings.

    I know that. That's why I had to ask you which you mean. But I do know
    a double conversion is running on DC, paralleled with the battery by some
    means. Hence it is deriving AC power from the DC. It is not a straight
    pass through.


    | Another thing, don't think that a double conversion UPS will protect a load
    | from all outages, voltage sags, or voltage swells. We find MANY units that
    | will drop the load for certain input conditions that are not out of the
    | ordinary.

    Theoretically faulty units, then. Maybe lots of the products do that.
    But then I'd say lots are faulty.

    OTOH, I have see double conversion UPSes that cut the input AC to DC
    conversion, effectively going to battery, at the slightest twitch in the
    AC input. But the load remained solidly powered.


    | A lot of what you ask depends on the size of UPS. We have done extensive
    | testing on UPS that are 2kVA and larger. Most of these do not plug into a
    | two pin Schuko, and they definitely have a terminal that is to be connected
    | to neutral. I will have to ask one of my test engineers about the smaller
    | units. I don't remember evaluating any.

    The Schuko could support up to 16 amps, though typical circuits using it
    in many countries are limited to 10 amps. So I can easily imagine that
    a UPS needing more than 8 amps could abandon the Schuko because in some
    places a dedicated circuit might be needed and those would be typically
    hardwired.

    If a UPS does pass neutral through, then it cannot bond it to the ground
    at the output, and hence is not a separately derived system. However, I
    see no reason to actually pass the neutral through on a dual conversion
    unit. Pass the ground through and ground one of the converter outputs so
    you have made a grounded conductor (technically not a neutral if the whole
    system is just 2-wire) and properly referenced the system to ground.

    Update:

    I just spoke to a tech support person at Powerware, and asked about the
    wiring issues. He did say that if the neutral was reversed on 120 volt
    models, they would refuse to start and give a wiring error status. But
    when I asked about the 230 volt models, and mentioned the possibility of
    systems with no neutral being supplied, he offered the information that
    their "high voltage" models "work fine on the dual hot wiring of 240 volts
    in the USA".

    I'll call some other manufacturers later in the week.

    --
    |---------------------------------------/----------------------------------|
    | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
    | first name lower case at ipal.net / |
    |------------------------------------/-------------------------------------|
     
    , Sep 20, 2006
    #5
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