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How common are full-power 208 volt ranges and dryers in the US?

Discussion in 'Electrical Engineering' started by Beachcomber, Jan 26, 2008.

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  1. Beachcomber

    Beachcomber Guest

    If you live in certain apartment or condo complexes in the US, you
    might be stuck with 208/120 volt service instead of the traditional
    split-phase 240/120 volt service common to single family houses. (The
    208 V. transformer secondary voltage is the result of a more
    economical 3-phase wye connection scheme available in urban areas that
    balances the load to a three-phase primary.) The upside of the
    208/120 service is that 3-phase power is available for elevators,
    pumps, etc.

    Just how readily available are electric dryers, for example, that
    operate on full-power at 208V instead of 240 V?

    I am aware that you can operate a 240V dryer on 208V, but the heating
    element will operate at 20% less capacity than at the higher voltage.
    The dryer is likely to run longer to get the clothes to dry.

    Googling around, I found that there are some dryers that can be
    ordered full power (lower resistance) at 208 V. (One source says that
    this is illegal or at least highly discouraged in Canada).

    I can understand that if you move your 208 V. dryer to a new home and
    put it on a 240 V. circuit, you may have a serious overheating
    problem.

    In general, I didn't find a lot of specific information on the
    Internet that addresses this concern about the difference in voltage.

    When these multi-unit buildings are constructed, do the developers
    actually specify and insist on 208 V. appliances or do they just
    install the more common 240 units and hope that no one notices or
    complains?

    Finally, is it the same deal for electric ranges that are connected to
    208/120 instead of 240/120 voltage? Are there full power 208 models
    that are readily available?

    Beachcomber
     
  2. Guest

    | If you live in certain apartment or condo complexes in the US, you
    | might be stuck with 208/120 volt service instead of the traditional
    | split-phase 240/120 volt service common to single family houses. (The
    | 208 V. transformer secondary voltage is the result of a more
    | economical 3-phase wye connection scheme available in urban areas that
    | balances the load to a three-phase primary.) The upside of the
    | 208/120 service is that 3-phase power is available for elevators,
    | pumps, etc.

    I'd rather see them run the "big stuff" on 480/277 or even 600/347.
    If it needs some "umph" to go, it could use some 480 or 600.

    Then put in 3 transformers to drop 480 or 600 down to 120/240 and
    divide the place up into 3 roughly equal sections. All the out of
    reach HID security lighting could be run directly on 277, 347, 480,
    or 600.

    The utility might not like the extra transformers involved, though.
    OTOH, some very large buildings do have transformers at various
    levels. I know the college dorm I lived in for a couple years had
    a transformer closet every 3 floors (and the lock on the door was
    NOT a part of the building master key system). I have no idea what
    the supply voltage was (whether it was 600 volt class or higher).
    But I do know the elevators were supplied by 480/277.


    | Just how readily available are electric dryers, for example, that
    | operate on full-power at 208V instead of 240 V?
    |
    | I am aware that you can operate a 240V dryer on 208V, but the heating
    | element will operate at 20% less capacity than at the higher voltage.
    | The dryer is likely to run longer to get the clothes to dry.

    Not accounting for resistance change due to temperature, at 208 volts
    there would be only 75% of the power used. So that would mean a 25%
    reduction. But at the lower temperature, the element would draw a bit
    more current since it would have slightly less resistance. But is
    that effect enough to put this in the 20% range? I don't have the
    formulas to figure that out. Is that where you get "20%"?


    | Googling around, I found that there are some dryers that can be
    | ordered full power (lower resistance) at 208 V. (One source says that
    | this is illegal or at least highly discouraged in Canada).

    You can get replacement heating elements designed for 208 volts for many
    models of dryers, stoves, water heaters, and I presume also for central
    heating systems. I don't know how well that addresses the increased
    current that would be drawn.

    But see below.


    | I can understand that if you move your 208 V. dryer to a new home and
    | put it on a 240 V. circuit, you may have a serious overheating
    | problem.

    Maybe. If the heating is thermostatically controlled, especially with
    solid state switching at a fast rate, it should be possible to have an
    element that handles a wide voltage range.

    My current kitchen stove has cooktop and oven elements that even at
    the highest settings are not on more than about 2/3 of the time. It
    seems to me they could handle 208 volts by being on for a longer time.

    Keep in mind that although an element designed for 208 volts would draw
    more current than one designed for 240 volts, when used at the design
    voltage, to produce the same heat, one that is thermostatically
    controlled would not matter so much. While it would have a higher
    current at the higher voltage and a lower current at the lower voltage
    to achieve the same heating, the heating effect on the wiring that
    supplies it, and on the thermal element in the breaker that protects
    that wiring, would follow the same pattern on average. It just needs
    to switch on and off fast enough to avoid heat surges. For a range
    of voltage from 208 to 240, on and off every 10 seconds or so could
    be enough.


    | In general, I didn't find a lot of specific information on the
    | Internet that addresses this concern about the difference in voltage.
    |
    | When these multi-unit buildings are constructed, do the developers
    | actually specify and insist on 208 V. appliances or do they just
    | install the more common 240 units and hope that no one notices or
    | complains?

    Apparently the latter happens a lot. But do not assume malice where
    mere incompetence can explain it. The developers might well not even
    know the issue at all.

    If I were developing a large building for residential purposes like
    that, though, I would be fighting to get normal genuine 120/240 in
    each unit.


    | Finally, is it the same deal for electric ranges that are connected to
    | 208/120 instead of 240/120 voltage? Are there full power 208 models
    | that are readily available?

    Absolutely yes, at least for older stuff (see above).

    My grandfather managed to get three phase power for his wood shop. But
    he made the mistake of getting it all on a single drop (the wood shop
    was a detached building, though not as easily reached by an overhead
    service drop). Apparently it was 208/120 wye/star, instead of 120/240
    center tapped delta. It was well known that the stove and electric water
    heater were always "slow". The A/C worked, but was especially sensitive
    to brownouts. The house was built around 1956.
     
  3. Beachcomber

    Beachcomber Guest

    I don't know Phil... The higher voltages are, in theory, more
    efficient. But it seems to me that there are distinct advantages to
    the North American system where no conductor entering a residential
    dwelling is at a potential of greater than the (nominal) 120 volts to
    ground.

    I still think the safety advantages of the lower voltage are of
    greater value than efficiences and savings and conductor size at the
    higher voltage (and the need to use one or more whole-house RCDs on a
    Euro wiring scheme).

    On the European 240 volt systems I've seen in the UK, for example, the
    conductors may be thinner, but then there is the awkwardness of the
    increased spacing requirements for the plugs and sockets, bigger and
    uglier receptacles, sockets that need to have switches on them for
    safety, the ban on anything but reduced voltage shaver outlets in the
    lavatories, and, if I'm not mistaken, isn't there also some overly
    restrictive rule about the placement of wall mounted bathroom light
    switches?

    Beachcomber
     
  4. Guest

    | On 26 Jan 2008 16:43:45 GMT, wrote:
    |
    |>
    |>| If you live in certain apartment or condo complexes in the US, you
    |>| might be stuck with 208/120 volt service instead of the traditional
    |>| split-phase 240/120 volt service common to single family houses. (The
    |>| 208 V. transformer secondary voltage is the result of a more
    |>| economical 3-phase wye connection scheme available in urban areas that
    |>| balances the load to a three-phase primary.) The upside of the
    |>| 208/120 service is that 3-phase power is available for elevators,
    |>| pumps, etc.
    |>
    |>I'd rather see them run the "big stuff" on 480/277 or even 600/347.
    |>If it needs some "umph" to go, it could use some 480 or 600.
    |>
    |
    | I don't know Phil... The higher voltages are, in theory, more
    | efficient. But it seems to me that there are distinct advantages to
    | the North American system where no conductor entering a residential
    | dwelling is at a potential of greater than the (nominal) 120 volts to
    | ground.

    These days, I would not be worried about 277 volts (L-G) entering my home.
    But _transitioning_ to something like 240 volts (L-G) would be a serious
    problem because people here are not accustomed to how to deal with it.
    But comparison, they know more about it, and respect it more, in UK and
    other places that have had it for decades. Of course ther are lots of
    other issues that would block such a change.

    OTOH, we could transition a lot of stuff over to the style of 240 volts
    we already have in the USA.


    | I still think the safety advantages of the lower voltage are of
    | greater value than efficiences and savings and conductor size at the
    | higher voltage (and the need to use one or more whole-house RCDs on a
    | Euro wiring scheme).

    With a 240 volt system having ground tapped in the middle, we the
    advantages of both. And we already get much of that by having the
    split pole system, when loads are reasonably near balance, as that
    means for the same kVA or kW load, we have the same current as UK
    would, at least on the service drop into the home. But I would like
    to extend that to other circuits in the home.


    | On the European 240 volt systems I've seen in the UK, for example, the
    | conductors may be thinner, but then there is the awkwardness of the
    | increased spacing requirements for the plugs and sockets, bigger and
    | uglier receptacles, sockets that need to have switches on them for
    | safety, the ban on anything but reduced voltage shaver outlets in the
    | lavatories, and, if I'm not mistaken, isn't there also some overly
    | restrictive rule about the placement of wall mounted bathroom light
    | switches?

    I think the spacing is legacy. Compare the UK plug/socket (I forget the
    designation) to the US NEMA 6-15 or 6-20. The spacing of the NEMA ones
    are just as close for 240 volts as for 120 volts. There is enough space
    for the voltage. I want have a power cord with a NEMA 6-15P on one end
    to use on my computers (I do know where to get them ... it's the outlets
    I need to have).

    What we could do better on are things like protecting pin contact by
    the time the pins have contacted the socket contacts. Insulating
    part of the pins would do this. The round pins of Europlug/Schuko and
    the thicker pins of the UK plug could do that easier than the US plug.

    I don't feel a need to have shutters that are opened by the ground pin.
     
  5. Beachcomber

    Beachcomber Guest

    Yes, we could add shutters to the plug pins and blades. I believe
    that there are already code compliant receptacles for children's rooms
    that do that sort of thing.

    But do you really think that having "baby-protected outlets"
    everywhere is necessary?

    There is a trade off and an added value in simplicity.

    Beachcomber
     
  6. bud--

    bud-- Guest

    The [US] NEC does. Required in the 2008 code for most 15/20A 120V
    receptacles in dwellings (406.11).
     
  7. Dean Hoffman

    Dean Hoffman Guest

    I think GFCI is required (2008 code) on all outlets not protected
    by arc fault protection. Shuttered outlets seem redundant. Is this a
    case of the left hand not knowing what the right hand is doing?

    Dean
     
  8. Guest

    |
    |>What we could do better on are things like protecting pin contact by
    |>the time the pins have contacted the socket contacts. Insulating
    |>part of the pins would do this. The round pins of Europlug/Schuko and
    |>the thicker pins of the UK plug could do that easier than the US plug.
    |>
    |>I don't feel a need to have shutters that are opened by the ground pin.
    |>
    |
    | Yes, we could add shutters to the plug pins and blades. I believe
    | that there are already code compliant receptacles for children's rooms
    | that do that sort of thing.

    But those are mechanical opening shutters. The ground pin does not have
    sufficient extra length to reliably open other shutters upon insertion.
    I presume the UK plug does (I've never obtained the exact dimensions or
    an instance of one of these).


    | But do you really think that having "baby-protected outlets"
    | everywhere is necessary?

    I would in areas where the "baby" might be left alone for a while. But
    these do not need to be the kind that block non-ground usage. They just
    need to be the kind that block non-parent usage. The kind that require
    sliding the shutter sideways manually while inserting the plug would do
    the job.
     
  9. Guest

    | bud-- wrote:
    |> Beachcomber wrote:
    |>>> What we could do better on are things like protecting pin contact by
    |>>> the time the pins have contacted the socket contacts. Insulating
    |>>> part of the pins would do this. The round pins of Europlug/Schuko and
    |>>> the thicker pins of the UK plug could do that easier than the US plug.
    |>>>
    |>>> I don't feel a need to have shutters that are opened by the ground pin.
    |>>>
    |>>
    |>> Yes, we could add shutters to the plug pins and blades. I believe
    |>> that there are already code compliant receptacles for children's rooms
    |>> that do that sort of thing.
    |>>
    |>> But do you really think that having "baby-protected outlets"
    |>> everywhere is necessary?
    |>
    |> The [US] NEC does. Required in the 2008 code for most 15/20A 120V
    |> receptacles in dwellings (406.11).
    |>
    |
    | I think GFCI is required (2008 code) on all outlets not protected
    | by arc fault protection. Shuttered outlets seem redundant. Is this a
    | case of the left hand not knowing what the right hand is doing?

    While I don't agree with a universal requirement for shuttered outlets,
    I do not see this as a case of left hand vs. right hand. There are things
    the shuttered outlet protects against that GFCI does not. I just don't
    think we need them in every dwelling outlet. It's simple enough to add
    them where needed. It's simple enough to replace them after the inspector
    is gone (and then donate the loose items to someone with actual babies).
     
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