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electric outlet for window AC question

Discussion in 'Electrical Engineering' started by ReadyToPuke, Jun 6, 2005.

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  1. ehsjr

    ehsjr Guest

    Don't lose the concept in the minutae. The 20 amp T slot
    receptacle serves two purposes: it allows devices with
    NEMA 5-20 's to be plugged in, and it also identifies
    the receptacle as being on a 20 amp branch. Manufacturers
    have to follow a host of rules/standards/practices etc,
    and to get UL listing, nust use the correct plug on
    cord and plug connected devices they make.

    The violation would occur if you wired a 20 amp receptacle on
    a 15 amp branch, regardless of what gets plugged in. As you
    noted in another post, 210.21(B) with a multiple receptacle
    (or receptacles) on the branch. A dedicated (meaning serving
    a single receptacle) 15 Amp circuit is ridiculous enough on
    its own without compounding it by makeing the receptacle
    20 amps.

    Ed
     
  2. Roy Q.T.

    Roy Q.T. Guest

    One Last Thing, For Ed & Phil : What you are saying is, You can't
    install a 20A Receptacle on a 15A circuit, but, you can install a 15A
    receptacle ona 20A circuit is that what you are saying the NEC allows
    here ? Roy


    From: (ehsjr)
    wrote:
    That's 80 percent of the BRANCH CIRCUIT rating. 80 percent of 20 amps is
    16 amps. So in theory, if I have multiple NEMA 5-15R receptacles on a 20
    amp branch circuit, I could draw up to 16 amps from one outlet and not
    violate this rule. I would not worry about it in a technical sense with
    respect to the receptacle since I know it is rated to 20 amps. The plug
    in use might not be, but 20 amp plugs don't appear to be any more robust
    than 15 amp plugs; they just have a twisted neutral.
    So which rule would I be violating if in this case a single
    cord-and-plug connected appliance draw more than 12 amps? What rule
    requires equipment over 12 amps to use a NEMA 5-20P or larger? A UL
    listing requirement?
    Don't lose the concept in the minutae. The 20 amp T slot receptacle
    serves two purposes: it allows devices with NEMA 5-20 's to be plugged
    in, and it also identifies the receptacle as being on a 20 amp branch.
    Manufacturers have to follow a host of rules/standards/practices etc,
    and to get UL listing, nust use the correct plug on cord and plug
    connected devices they make.
    The violation would occur if you wired a 20 amp receptacle on a 15 amp
    branch, regardless of what gets plugged in. As you noted in another
    post, 210.21(B) with a multiple receptacle (or receptacles) on the
    branch. A dedicated (meaning serving a single receptacle) 15 Amp circuit
    is ridiculous enough on its own without compounding it by makeing the
    receptacle 20 amps.
    Ed
     
  3. ehsjr

    ehsjr Guest


    A situation encountered in the field does not necessarily need
    to have a specific prohibition in the NEC in order for it to
    be rejected by the AHJ. See 110.3(A)(7). 110.3 (A) requires that
    the inspector evaluate the installation for the items listed.
    Item (7) does not prohibit a 20 amp receptacle on a 15 amp
    branch, per se, but does prohibit it, de facto .

    Ed
     
  4. ehsjr

    ehsjr Guest

    Yes.
    Ed
     
  5. Roy Q.T.

    Roy Q.T. Guest

    From: (ehsjr)
    Roy Q.T. wrote:
    One Last Thing, For Ed & Phil : What you are saying is, You can't
    install a 20A Receptacle on a 15A circuit, but, you can install a 15A
    receptacle ona 20A circuit is that what you are saying the NEC allows
    here ? Roy

    Yes.
    Ed

    Then : You are right per se, and quite wrong de facto };-) Okay', and I
    understand this very well , but I just hate it when posters assume that
    the cat has 5 legs and start slinging crap around, like we have time to
    toss the ball around in here. Roy
     
  6. ehsjr

    ehsjr Guest

    A 15 amp receptacle is manufactured to the same specs as a 20
    amp receptacle, in terms of the current carrying capability.
    The only difference is that the 20 amp receptacle has a T slot
    so it can accept flat blades at 90 degress to one another.
    The 15 amp can't accept those 90 degree offset blades.

    The idea that a 20 amp receptacle can handle more current
    than a 15 amp receptacle, without burning/melting or otherwise
    becoming defective, is incorrect.

    Ed

    Okay', and I
     
  7. Roy Q.T.

    Roy Q.T. Guest

    I don't think so Ed; There are a variety of them and i read recently
    that the specs for a 15 & 20 amp receptacles are different, they might
    seem the same but the metals employed are tempered differently and their
    capacity is limited to there rating.

    Believe me I am not making this up: A 15 Amp circuit will trip if it
    goes over the rated current with both 15 & 20A with no ill effects on
    them, but, the study specifically mentioned that 15A units on a 20A
    circuit can suffer as any underrated equipment used on the supply or
    convenience outlet circuitry., I do not think much of it either and have
    bought random duplex receptacles without minding there current ratings
    and am just a little self conscious about it now since this came up on
    this thread.,Given my past observations I am just reiterating the
    concept of careful circuit component matching to myself };-)
    ®oy
     
  8. ehsjr

    ehsjr Guest

    Thanks, Roy!

    I would love to read the article if you can find it.
    My information came from UL and is dated 1991 - so
    if there is something new that superceeds it, I am
    eager to learn.

    Ed
     
  9. John Gilmer

    John Gilmer Guest

    ..
    I doubt it.

    Seems that "no one" makes a 120 volt gadget that draws more than 15 amps!
    (Even if it claims to have severl horse power motor!)

    With the exception of electric stoves and clothes dryers, 240 outlets are as
    rare as hen's teeth with only a few being put in to support larger sized
    window air conditioners. Often these just "patch" onto the electric dryer
    circuit.

    Must of this thread has been quite silly and pointless.
     
  10. John Gilmer

    John Gilmer Guest

    Well, I saw on in a house that was "modern" in 1958 but had a fuse box. It
    did have the "heavy" circuits for the stove and dryer, however.

    Folks put in these BIG window units because they don't have the money to put
    in Central Air and install an entirely new service. I never "opened up"
    such an installation, but dryer circuits are often/usually just 30 amps so
    #10 romex would be protected. It may not be "code" but it's not asking
    for trouble either.
    True. But even if you are taking short cuts it doesn't mean you don't want
    to be a safe as you can manage without spending an arm and a leg.

    It seems to me that the folks who create the NEC sometimes DO worry about
    economy and DO reason that it's better to have GOOD safety at reasonable
    cost over GREAT safety at a cost that encourages folks to just jury rig. But
    when they mandated the "arc detection breaker" I wondered.
    Well, since we are on the subject:

    I notice that the "dryer and stove" outlets with only three wires
    (chassis/neutral are bonded in the appliance) don't make any effort to
    connect neutral before hot. Of course, for the last 30 years dryers are
    completely "off" until you push the start button and the only 120 volt loads
    in the stove are the lamp and the timer so ...)
    Fine. Put in a "questions and comments" BB if you can.
     
  11. John Gilmer

    John Gilmer Guest

    Why not?

    http://ka9wgn.ham.org/ |
    ---
     
  12. ehsjr

    ehsjr Guest

    Thanks, Tom!
     
  13. Bud

    Bud Guest


    Hard to believe but apparently true. A single outlet just has to have a
    higher rating than the branch circuit. Not only can you put a 20 amp
    single receptacle on a 15 amp circuit you can put a 30 amp, 100 amp ....

    This appears to have been in effect at least back into the 1980s.

    One way to see check the reasoning behind a code item is to look for
    proposed changes and see how the code making panel responds. There were
    no proposed changes to this rule as far back as 1983 (1996 and 1993 are
    unknown). This rule was invisible?

    Bud--
     
  14. John Gilmer

    John Gilmer Guest

    WTF do you mean by "no juction boxes?"

    What IS a "junction box" according to PA these days?
     
  15. w_tom

    w_tom Guest

    Where do these numbers come from? 15 amp wire cannot blow a
    20 amp breaker? Nonsense. From Automatic Electric, the
    continuous current for fusing a copper 18 AWG wire is 82.9
    amps. Therefore an 18 AWG wire can carry more than 82
    intermittent amps - for the milliseconds necessary to trip a
    breaker.

    15 amp receptacles must installed in those rooms. Idea
    being a six foot power cord on any appliance would always be
    long enough to connect to a wall receptacle. Those 15 amp
    receptacles can be powered by 20 amp circuits.

    But again, how reliable is the source when short term
    amperage for an 18 AWG zip cord is more than sufficient to
    safety trip a 20 amp breaker. The important parameter is
    time. Those 'more than 20 amps' must exist only for a short
    period. 18 AWG wire is more than sufficient to trip a 20 amp
    breaker during a short 'short circuit'.
     
  16. Bud

    Bud Guest

    It actually takes a lot longer than one might guess to trip a breaker
    (or fuse). Most circuit breakers have a thermal trip element, which is
    like a fuse with a time delay - it won't trip, for example, on a motor
    start. For Sqare D, 80 amps on 20 amp breaker has a minimum clearing
    time of 6 seconds. Above 200 amps the maximum clearing time is 1 cycle.

    Bud--
     
  17. Bud

    Bud Guest


    You may be interested in this - from the Product Safety Technical
    Committee of the IEEE EMC Society:


    In North America, wire sizes
    for power cords, including extension
    cords, are selected to always
    be capable of blowing the 15 or
    20 amp building fuse in the event
    of a steady-state short-circuit at
    the end of the power cord.

    The power cord wire size together
    with its insulation rating
    must have a sufficiently low
    impedance to withstand the
    overheating of the short-circuit
    until the 20-amp circuit breaker
    clears the circuit. (Cord-connected
    electrical heating appliances often
    have high temperature insulation
    on their power cords to account
    for steady-state high current conditions.

    To meet this criterion, the
    minimum wire size for flexible
    cords is AWG 18, except for
    specific applications, in which
    case there are extensive insulation
    robustness tests designed to
    preclude insulation failure.
    Ampacity ratings of cords and
    cordsets are given in UL 817,
    Table 90. These ratings are for
    normal conditions.
     
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