Re: T-slot plugs and 20 amp appliances?

Discussion in 'Electrical Engineering' started by phil-news-nospam@ipal.net, May 28, 2008.

  1. Guest

    On Tue, 27 May 2008 22:26:05 -0500 Bill Shymanski <> wrote:

    | All this discussion of 240-volt appliances has me wondering about the
    | fairly recent US and Canadian electrical code changes that encourage us
    | to install the t-slot 20 Amp receptacles in places like kitchens. But
    | now I wonder why. Aside from providing some indication that the branch
    | circuit was wired with slightly heavier wire, are there any consumer
    | products out there that use the 20-amp style plug?
    |
    |
    | I'll have to look to see if I can find the NEC discussions on the rule
    | amendment that allowed the T-slot plugs. I'm curious as to the
    | motivation for this.

    If you are referring to "allowing" the NEMA 5-20R outlets, they have been
    allowed for a long time, at least as far back as the 1960's when I first
    saw one. They are required for a single dedicated outlet that has 20A
    circuit protection (although arguably, this is pointless). Where a NEMA
    5-20R is used, the circuit must be protected at 20A and thus must have a
    rating of 20A. But you can use NEMA 5-15R on a 20A circuit which has more
    than one outlet.

    The NEMA 5-20R has a T-slot only on the grounded conductor blade. This allows
    it to fit either a NEMA 1-15P, NEMA 1-20P, NEMA 5-15P or NEMA 5-20P. The NEMA
    5-20P has the grounded conductor blade turned 90 degrees and offset outward to
    maintain the 1/2 inch spacing between the blades. The NEMA 2-20P may also fit
    but this would have problems if plugged in that way since it would be for an
    older 240V ungrounded appliance now getting only 120V.

    The NEMA 6-20R also has one T-slot, but that T-slot is on the side of the
    outlet corresponding to the side the hot conductor is on in a 5-15/20.
    Both conductor slots are hot at 120V relative to ground, but the one on
    the right when the ground pin is down (left when ground is up) is the one
    that has the T-slow for these 240V outlets.

    The legacy T-slot outlet was an ungrounded outlet that had the T-slot hole
    for both conductors. I still occaisionally see them around on very old
    wiring. The intent was to be a single product usable for either 120V or
    240V circuits. You can see the risks it exposed. It would not be allowed
    today, and may not have ever been technically allowed.

    Based on the 80% rule and assuming exactly 120V and 240V, appliances could
    use these plugs for these wattage or volt-amp ratings:

    5-15P 1440
    5-20P 1920
    6-15P 2880
    6-20P 3840

    Although I would rather use 240V in these (and other [*]) cases, I have seen
    some appliances with a NEMA 5-20P though I don't recall if any were things
    you might commonly see in a kitchen.

    Is your reference to "encourage us to install the t-slot 20 Amp receptacles"
    in reference to the NEMA 5-20R?

    There is a difference between "encourage" and "allow".

    I do not see anything in the NEC 2008 code that encourages or requires NEMA
    5-20R outlets on the kitchen circuits (that have to be 20A). They are allowed
    and in all places I've seen that might be recent installs, are used. As long
    as the circuit has at least 2 outlets (a duplex receptacle does this), then
    NEMA 5-15R outlets are sufficient. See NEC 210.21(B)(1) and (3).

    The only case where you would be required to have NEMA 5-20R outlets in a
    kitchen is if you meet NEC 210.11(C)(1) through the use of a dedicated branch
    circuit for each single outlet, per NEC 210.21(B)(3).

    I would actually prefer to use NEMA 5-15R only to meet the minimum kitchen
    requirements in NEC 210.52, and supplement that with 2 or more NEMA 5-20R
    on separate dedicated branch circuits. Heavier appliances would thus be
    kept apart from the multi-outlet circuits. I'd also have NEMA 6-20R for
    even heavier kitchen appliances like a 2400 watt microwave.

    My layout might be like this:
    http://phil.ipal.org/usenet/aee/2008-05-28/ks-3.html

    Let me know if you find the rule in NEC you are looking for that allows the
    T-slot plugs (I think you mean outlets) if it is not NEC 210.21(B)(3).

    [*] I'm all for deleting NEC 210.6(A)(2) or at least making it not apply to
    single family dwelling units.

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    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , May 28, 2008
    #1
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  2. Stephen B. Guest

    <> wrote in message
    news:...
    <SNIP>
    >
    > The legacy T-slot outlet was an ungrounded outlet that had the
    > T-slot hole
    > for both conductors. I still occaisionally see them around on very
    > old
    > wiring. The intent was to be a single product usable for either
    > 120V or
    > 240V circuits. You can see the risks it exposed. It would not be
    > allowed
    > today, and may not have ever been technically allowed.


    I think I just replaced on of these. Are you saying that it was
    desighned to be wired ether to a 120v curcuit (using the standard
    vertical " | | " plug) or a 240v curcuit (using a "- -" plug)?

    Is a "- -" plug standard for 240v? if so what amprage?

    Just curious (mine was definatly a 120v 15a curcuit

    --

    Stephen B.
    Remove One Spam only to connect directly
     
    Stephen B., May 28, 2008
    #2
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  3. "Stephen B." <> wrote in message
    news:7gl%j.15455$2C.3987@trndny08...
    >
    > <> wrote in message
    > news:...
    > <SNIP>
    >>
    >> The legacy T-slot outlet was an ungrounded outlet that had the T-slot
    >> hole
    >> for both conductors. I still occaisionally see them around on very old
    >> wiring. The intent was to be a single product usable for either 120V or
    >> 240V circuits. You can see the risks it exposed. It would not be
    >> allowed
    >> today, and may not have ever been technically allowed.

    >
    > I think I just replaced on of these. Are you saying that it was desighned
    > to be wired ether to a 120v curcuit (using the standard vertical " | | "
    > plug) or a 240v curcuit (using a "- -" plug)?
    >
    > Is a "- -" plug standard for 240v? if so what amprage?
    >
    > Just curious (mine was definatly a 120v 15a curcuit
    >




    There is a 120v/20A plug that looks like | -- , this is what they are
    talking about. The standard 120V/15A plug has | |, and the 20A version has
    | -- (or -- | ) configuration.
     
    Jeff Strickland, May 29, 2008
    #3
  4. Stephen B. Guest

    "Jeff Strickland" wrote
    >
    > "Stephen B." wrote in message
    >> <> wrote in message
    >> news:...
    >> <SNIP>
    >>>
    >>> The legacy T-slot outlet was an ungrounded outlet that had the
    >>> T-slot hole
    >>> for both conductors. I still occaisionally see them around on
    >>> very old
    >>> wiring. The intent was to be a single product usable for either
    >>> 120V or
    >>> 240V circuits. You can see the risks it exposed. It would not be
    >>> allowed
    >>> today, and may not have ever been technically allowed.

    >>
    >> I think I just replaced on of these. Are you saying that it was
    >> desighned to be wired ether to a 120v curcuit (using the standard
    >> vertical " | | " plug) or a 240v curcuit (using a "- -" plug)?
    >>
    >> Is a "- -" plug standard for 240v? if so what amprage?
    >>
    >> Just curious (mine was definatly a 120v 15a curcuit
    >>

    >
    >
    >
    > There is a 120v/20A plug that looks like | -- , this is what they
    > are talking about. The standard 120V/15A plug has | |, and the 20A
    > version has | -- (or -- | ) configuration.
    >


    I know about the standard "T" plug for 20 amps. I think phil was
    referencing to a very old double "T" outlet ie "--| |--"
    I replaced one like that reciently that I am certain was never hooked
    up to more than 15 amp along with about 5 other outlets and 3 ceiling
    lights.


    --
    Stephen B.
    Remove the first Spam only to e-mail directly
     
    Stephen B., May 29, 2008
    #4
  5. Guest

    On Thu, 29 May 2008 04:44:38 GMT Stephen B. <> wrote:
    | "Jeff Strickland" wrote
    |>
    |> "Stephen B." wrote in message
    |>> <> wrote in message
    |>> news:...
    |>> <SNIP>
    |>>>
    |>>> The legacy T-slot outlet was an ungrounded outlet that had the
    |>>> T-slot hole
    |>>> for both conductors. I still occaisionally see them around on
    |>>> very old
    |>>> wiring. The intent was to be a single product usable for either
    |>>> 120V or
    |>>> 240V circuits. You can see the risks it exposed. It would not be
    |>>> allowed
    |>>> today, and may not have ever been technically allowed.
    |>>
    |>> I think I just replaced on of these. Are you saying that it was
    |>> desighned to be wired ether to a 120v curcuit (using the standard
    |>> vertical " | | " plug) or a 240v curcuit (using a "- -" plug)?
    |>>
    |>> Is a "- -" plug standard for 240v? if so what amprage?
    |>>
    |>> Just curious (mine was definatly a 120v 15a curcuit
    |>>
    |>
    |>
    |>
    |> There is a 120v/20A plug that looks like | -- , this is what they
    |> are talking about. The standard 120V/15A plug has | |, and the 20A
    |> version has | -- (or -- | ) configuration.
    |>
    |
    | I know about the standard "T" plug for 20 amps. I think phil was
    | referencing to a very old double "T" outlet ie "--| |--"
    | I replaced one like that reciently that I am certain was never hooked
    | up to more than 15 amp along with about 5 other outlets and 3 ceiling
    | lights.

    That is exactly what I was referencing.

    --
    |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
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    | Usenet from these places, find another Usenet provider ASAP. |
    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , May 29, 2008
    #5
  6. Guest

    On Wed, 28 May 2008 23:56:17 GMT Jeff Strickland <> wrote:
    |
    | "Stephen B." <> wrote in message
    | news:7gl%j.15455$2C.3987@trndny08...
    |>
    |> <> wrote in message
    |> news:...
    |> <SNIP>
    |>>
    |>> The legacy T-slot outlet was an ungrounded outlet that had the T-slot
    |>> hole
    |>> for both conductors. I still occaisionally see them around on very old
    |>> wiring. The intent was to be a single product usable for either 120V or
    |>> 240V circuits. You can see the risks it exposed. It would not be
    |>> allowed
    |>> today, and may not have ever been technically allowed.
    |>
    |> I think I just replaced on of these. Are you saying that it was desighned
    |> to be wired ether to a 120v curcuit (using the standard vertical " | | "
    |> plug) or a 240v curcuit (using a "- -" plug)?
    |>
    |> Is a "- -" plug standard for 240v? if so what amprage?
    |>
    |> Just curious (mine was definatly a 120v 15a curcuit
    |>
    |
    |
    |
    | There is a 120v/20A plug that looks like | -- , this is what they are
    | talking about. The standard 120V/15A plug has | |, and the 20A version has
    | | -- (or -- | ) configuration.

    If the plug does NOT have a ground pin, then "| -" and "- |" are just the
    same thing turned 180 degrees. It represents 240V 20A ungrounded. It has
    a designation NEMA 2-20. A NEMA 2-20P plug will mate with a NEMA 6-20R
    outlet. It will also mate with a NEMA 5-20R which can be a problem for an
    appliance that could be a hazard operating on a lower voltage. There is a
    NEMA 1-20 for 120V 20A ungrounded. It has a vertical blade/slot and one
    with a short angle on it. It will mate with a NEMA 5-15R/5-20R combination,
    but not with a NEMA 5-20R-only that is designed to not accept NEMA 5-15P
    (and not with any 240V outlet configuration).

    A more interesting receptacle configuration is the NEMA 14-15R. It accepts
    both a NEMA 14-15P as well as a NEMA 6-15P. The NEMA 14-15R is a NEMA 6-15R
    with an added "-" blade above (for ground pin down) the other "- -" blades
    to add the neutral conductor. I have not seen this manufactured anywhere.

    You can see a NEMA 14-15R example in these illustrations for simplex and
    duplex configurations:

    http://phil.ipal.org/usenet/aee/2008-05-29/fourfaces.html
    http://phil.ipal.org/usenet/aee/2008-05-29/twelvefaces.html

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    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , May 29, 2008
    #6
  7. Guest

    Re: T-slot plugs and 20 amp appliances?

    On Fri, 30 May 2008 13:00:36 +0000 (UTC) Michael Moroney <> wrote:
    | writes:
    |
    |>A more interesting receptacle configuration is the NEMA 14-15R. It accepts
    |>both a NEMA 14-15P as well as a NEMA 6-15P. The NEMA 14-15R is a NEMA 6-15R
    |>with an added "-" blade above (for ground pin down) the other "- -" blades
    |>to add the neutral conductor. I have not seen this manufactured anywhere.
    |
    | Interesting. I never knew that existed. I have a duplex recepticle that
    | has a 5-15R on the top and a 6-15R on the bottom. Since the neutral has
    | to be there anyway, they could have added the extra pin easily to the
    | bottom outlet. But as you mention the 14-15R is either rare or
    | nonexistent. (my duplex outlet itself is oddball)

    That duplex is still manufactured by at least Hubbell and Leviton.


    | BTW a "face" you don't have is a 347V 15A outlet. It has one horizontal
    | "eye" and one slanted "eye" like the 7-15R. I wonder if it (and the
    | 277V 15A 7-15R outlet) are also merely theoretical or are there devices
    | that actually use them.

    That would be a NEMA 24-15R. The 24-20R is a mirror image of it. I have
    seen the 7-15R duplex in the Leviton catalog.

    --
    |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
    | by the abuse department, bellsouth.net is blocked. If you post to |
    | Usenet from these places, find another Usenet provider ASAP. |
    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , May 31, 2008
    #7
  8. Guest

    Re: T-slot plugs and 20 amp appliances?

    On Fri, 30 May 2008 12:39:37 +0000 (UTC) Michael Moroney <> wrote:
    | writes:
    |
    |>The legacy T-slot outlet was an ungrounded outlet that had the T-slot hole
    |>for both conductors. I still occaisionally see them around on very old
    |>wiring. The intent was to be a single product usable for either 120V or
    |>240V circuits. You can see the risks it exposed. It would not be allowed
    |>today, and may not have ever been technically allowed.
    |
    | I still have a couple of these, and for a long time I wondered about the
    | intent of the T slot. House was built in 1940.

    I'm guess they are installed in place. If you ever decide to replace them
    in the wall, keep the original devices. They could be valuable antiques.

    --
    |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
    | by the abuse department, bellsouth.net is blocked. If you post to |
    | Usenet from these places, find another Usenet provider ASAP. |
    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , May 31, 2008
    #8
  9. Guest

    Re: T-slot plugs and 20 amp appliances?

    On Wed, 4 Jun 2008 15:52:24 +0000 (UTC) Michael Moroney <> wrote:

    | writes:
    |
    |>The legacy T-slot outlet was an ungrounded outlet that had the T-slot hole
    |>for both conductors. I still occaisionally see them around on very old
    |>wiring. The intent was to be a single product usable for either 120V or
    |>240V circuits. You can see the risks it exposed. It would not be allowed
    |>today, and may not have ever been technically allowed.
    |
    | FWIW,I just saw an old (1946) Sylvester/Tweety Bird cartoon and it showed
    | one of these T slot duplex outlets. What was odd was the outlet faces
    | were rotated 90 degrees, which I've never seen in a real outlet.

    I don't follow what kind of rotation this was. There are some possibilities
    that I can imagine:

    1. The whole duplex was rotated, making each of the two outlets left and right
    of each other. The ends of the T's are up and down.

    2. Each of the 2 outlets was independently rotated, while remaining one above
    the others. The ends of the T's are up and down.

    3. Just the T's themselves are rotated. That would look weird.

    4. A combination of rotating the duplex and rotating the outlets. This would
    have left and right outlets, but leaving the ends of the T's sideways as
    they were before.

    See also:

    http://phil.ipal.org/usenet/aee/2008-06-04/want.html

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    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , Jun 4, 2008
    #9
  10. Guest

    Re: T-slot plugs and 20 amp appliances?

    On Wed, 04 Jun 2008 19:22:24 -0500 Bill Shymanski <> wrote:

    | In an old book on wiring I saw a picture of a duplex outlet used for DC
    | - it also had a T-slot but had the t and straight slot arranged
    | vertically. No ground pin, of course. I've never seen anything that
    | described standards for DC wiring - I suspect any books on that would be
    | before WWII at least.

    And a book that old would very likely be unrelated to today's standards on
    safety.

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    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , Jun 5, 2008
    #10
  11. Guest

    Re: T-slot plugs and 20 amp appliances?

    On Thu, 5 Jun 2008 02:04:31 +0000 (UTC) Michael Moroney <> wrote:
    | writes:
    |
    |>On Wed, 4 Jun 2008 15:52:24 +0000 (UTC) Michael Moroney <> wrote:
    |
    |>| FWIW,I just saw an old (1946) Sylvester/Tweety Bird cartoon and it showed
    |>| one of these T slot duplex outlets. What was odd was the outlet faces
    |>| were rotated 90 degrees, which I've never seen in a real outlet.
    |
    |>I don't follow what kind of rotation this was. There are some possibilities
    |>that I can imagine:
    |
    |>1. The whole duplex was rotated, making each of the two outlets left and right
    |> of each other. The ends of the T's are up and down.
    |
    |>2. Each of the 2 outlets was independently rotated, while remaining one above
    |> the others. The ends of the T's are up and down.
    |
    |>3. Just the T's themselves are rotated. That would look weird.
    |
    |>4. A combination of rotating the duplex and rotating the outlets. This would
    |> have left and right outlets, but leaving the ends of the T's sideways as
    |> they were before.
    |
    | I'm not sure I understand what #3 is, but what I meant is #2. The
    | outlets are one above the other the way most are currently, but a normal
    | flat blade (120V) plug would go in with the blades horizontal, one above
    | the other.
    |
    | Like this:
    |
    | |
    | ---
    |
    | ---
    | |
    |
    |
    | |
    | ---
    |
    | ---
    | |

    I do recall seeing an outlet oriented like that, but it was a single not a
    duplex. But a duplex would be entirely plausible as increased use of this
    new-fangled electricity took place.


    | I think I saw another outlet like this in another cartoon but mounted
    | horizontally, thus like #4. It was a while ago that I saw that.

    Mounting outlets horizontally, so one is left or right of the other, is
    common in Europe. I see advantages to it and would like to do that for
    my home. But I still want the ground pin on the up side, not left or
    right.


    | Another odd one we had when I was a kid. A combination outlet/faceplate
    | that had 5 two blade outlets in a normal duplex box size. Yes they all
    | (barely) fit! You could only plug the smaller lamp cord plugs in if
    | you wanted to use them all. I wish I kept it when the neighbors
    | renovated the place (we moved next door). This just had the vertical
    | slots, no T slots. Obviously no ground pins (no room!).

    I remember seeing something somewhat like that once. It had 2 very LONG slots
    and you could squeeze in more plugs if they were thin. No ground.

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    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , Jun 5, 2008
    #11
  12. Guest

    Re: T-slot plugs and 20 amp appliances?

    On Thu, 05 Jun 2008 00:23:31 -0400 Eric <> wrote:

    |> Another odd one we had when I was a kid. A combination outlet/faceplate
    |> that had 5 two blade outlets in a normal duplex box size. Yes they all
    |> (barely) fit! You could only plug the smaller lamp cord plugs in if
    |> you wanted to use them all. I wish I kept it when the neighbors
    |> renovated the place (we moved next door). This just had the vertical
    |> slots, no T slots. Obviously no ground pins (no room!).
    | I took out one that had 3 in one. I had never seen that before. No
    | grounds of course.

    Something like this?

    http://static.zoovy.com/img/kyledesign/-/light_switchplates/whitedespardswitchesoutlets

    --
    |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
    | by the abuse department, bellsouth.net is blocked. If you post to |
    | Usenet from these places, find another Usenet provider ASAP. |
    | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
     
    , Jun 5, 2008
    #12
  13. Roy Guest

    Re: T-slot plugs and 20 amp appliances?

    From:
    On Thu, 05 Jun 2008 00:23:31 -0400 Eric <> wrote:
    Another odd one we had when I was a kid. A combination outlet/faceplate
    that had 5 two blade outlets in a normal duplex box size. Yes they all
    (barely) fit! You could only plug the smaller lamp cord plugs in if you
    wanted to use them all. I wish I kept it when the neighbors renovated
    the place (we moved next door). This just had the vertical slots, no T
    slots. Obviously no ground pins (no room!).
    | I took out one that had 3 in one. I had never seen that before. No |
    grounds of course.
    Something like this?
    http://static.zoovy.com/img/kyledesign/-/light_switchplates/whitedespardswitchesoutlets
    --
    |WARNING: Due to extreme spam, googlegroups.com is blocked. Due to
    ignorance | |         by the abuse department, bellsouth.net is
    blocked. If you post to | |         Usenet from these places,
    find another Usenet provider ASAP.       | | Phil Howard KA9WGN
    (email for humans: first name in lower case at ipal.net) |
    -----------------------------
    I've got one of those ready to go }:) mine is offwhite/cream, drk brn
    insets/rocker., you can ground it from the mounting bracket, those snap
    in parts are funny that way....I have seen the 3prong outlet snap on
    too, with the grn. screw for bonding and all..

    Roy Q.T. ~ US/NCU ~ E.E. Technician
    [have tools, will travel]
     
    Roy, Jun 6, 2008
    #13
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