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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. w_tom

    w_tom Guest

    Don't expect a coherent response from Roy Q.T. who attacks
    when he really does not know. 15 amp receptacles known as
    NEMA 5-15 are legal on circuits powered by 20 amp breakers -
    regardless of what Roy Q.T. feels.

    A standard 15 amp receptacle powered by 20 amp circuits:
    http://www.elect-spec.com/nema_515psx2aa.jpg

    Notice the difference from a 20 amp wall receptacle:
    http://www.elect-spec.com/nema_520psx1a.jpg

    Contrary to what Roy Q. T. posted, 15 amp wall receptacles
    are used on 20 amp circuits.

    Meanwhile, unanswered is whether code changes permit or ban
    larger amp receptacles powered by smaller amp circuit
    breakers. From previous code citations, apparently, a code
    change has occured. What changed when, and what are the most
    recent code requirement?
     
  2. operator jay

    operator jay Guest

    Defrost heaters.

    One reason I want to know is that I see
    http://ka9wgn.ham.org/ |
    ---
     
  3. John Gilmer

    John Gilmer Guest

    The "usual suspect" is insufficient air flow to keep the coil temperature
    about freezing. When you can independently vary the speed of the "inside"
    and "outside" fans, then it's possible to control the humidity by running
    the fan at a lower speed until the humidity is reduce to a preset level.
    Any particular coil is limited in the amount of moisture it can remove
    (rather than the moisture condensing an then blowing back into the living
    space.)

    Under certain circumstances, low refrigerant can cause the problem. When
    happens is that the pressure in the "low" side (the inside coil" get's so
    low that the little refrigerant that's left creates a small area in the coil
    that"s well below the freezing point of water. That part of the coil
    "freezes up" and insulates the coil there. The point where the refrigerant
    vaporizes in the coil continues along the junction between the ice and just
    liquid water. Usually, however, low refrigerant will cause "no cooling."
    This doens't happen often because the "cooling" capacity of a unit that's
    very low on refrigerant isn't much and ice does conduct a little heat.

    Nope! It's thermostat will just shut off the compressor when the return
    air temperature falls below the set point. As others have notes, it will
    tend to short cycle.
     
  4. ehsjr

    ehsjr Guest

    Well, if I understand the limited amount of reading I have
    done on some of the newer split AC units (like the Mitsubishi
    "Mr. Slim"), they use a VFD to run the compressor. I *assume*
    that the coils would be less cool/more cool as the VFD
    varies. I hope someone who *knows* about these units will
    chime in with the facts.

    Ed
     
  5. Roy Q.T.

    Roy Q.T. Guest

    I'm shocked to read that FireMan Tom would suggest that the NEC allows
    for a 15Amp device on a 20Amp protected circuit...It does Not Allow for
    that, & it is a violation albeit a mild one, but nevertheless improper &
    Not Recommended. All he's done is attack every reply i post here... and
    now he's just being ridiculous and harmful.He must think I'm some punk
    tech from his township., I've been doing Electrical Troubleshooting &
    Installations for over 30 years and seen plenty stupidity like that go
    unchecked because they believe in the " pros " that did it, and not in
    the letter of the codes and the wording of the specifications and
    experience.


    After all: He is a Fireman, he lives for the Sinister Fire to take hold
    of your property so he can do his job., didn't know he'd stoop to that
    level though to insure future work. What happened to Better Safe than
    Sorry ?

    Leave it alone; Get the proper sized Receptacle & Breaker for the new
    circuit you are running for your Air Conditioner.
    I'm through with this.......
    Roy
     
  6. daestrom

    daestrom Guest

    There are also solid-state proportional heater controls, that use
    phase-controlled thyristors to vary the heat output over a continuous range.
    Usually not cost effective for simple space heating, but often used where
    more precise temperature control is needed.
    There is a lot I could go into in this area. The base temperature of the
    evaporator is determined by the saturation pressure of the refrigerant
    inside it. Advanced systems use a variety of suction pressure controls to
    maintain this saturation condition just above 32F. In a high-end system,
    suction throttle valves (a form of 'back-pressure' regulator) will maintain
    the saturation temperature in the evaporator at between 35 and 45 F. This
    is cold enough to condense a lot of the water vapor, but will still leave
    some in the air. When air is at 100% RH at 40F, and then warmed back to 70
    F, it will be about 50% RH.

    Another pressure control method is various forms of 'staging' in the
    compressor, or the use of variable speed compressors. By controlling the
    amount of pumping the compressor does, the evaporator pressure is kept above
    freezing. Interestingly, in modern auto A/C, there is a suction pressure
    switch that cycles the compressor on/off by engaging/disengaging the clutch
    used to drive it. Of course, cycling a motor driven compressor on/off is
    not viable as it would have to do this several times a minute, and the
    repeated high starting currents will burn out the motor.

    Contrary to urban myth, the TXV (ThermoeXpansion Valve) is *NOT* used to
    prevent freezeups. It works by sensing both the pressure and temperature at
    the evaporator outlet, and is used to control the amount of superheat in the
    refrigerent as it leaves the coil. A small amount of superheat is desired
    to prevent the compressor from ingesting liquid (that would damage the
    compressor). But amateurs will often 'fiddle' with the TXV when either the
    unit freezes up or doesn't cool properly.

    One cause of freeze-ups is too little charge in simple capillary units (no
    TXV). The lower pressure in the system causes the evaporator to run at
    lower temperatures.

    And finally, despite what I wrote above, there *are* some cheap units that
    are designed to have the evaporator running below 32F. These cheap units
    rely on a high air flow to keep the evaporator warm enough to avoid a build
    up of frost. They don't work well in humid climates. The best you can do
    with these is to make sure the air flow is unobstruted by dirty filters.

    daestrom
     
  7. daestrom

    daestrom Guest

    How do you explain the common, and 'allowed' practice of using several 15A
    receptacles on a branch circuit with 12AWG wire and a 20A circuit breaker??

    Mind you, that is *not* for the dedicated circuit we're talking about here.
    A dedicated, single outlet circuit should have a 20A receptacle for a 20A
    circuit.

    daestrom
     
  8. John Gilmer

    John Gilmer Guest

    "Easily?" Nah!

    It can happen but simple stuff like a thermostat in the main distribution
    duct (before the dampners) that would either shut off the compressor or over
    ride a "decision" to close a dampner can "solve" that problem.

    If ALL zones are satisfied, the compressor should shut down in any case.
     
  9. ehsjr

    ehsjr Guest

    Gee Roy, You responded to my post, which contained
    nothing of what Tom said, nor anything about the
    use of 15A receptacles on a 20 amp circuit.

    For the record, it is allowed in the NEC. Note that
    you must have more than one receptacle on the circuit.

    Ed
     
  10. Roy Q.T.

    Roy Q.T. Guest

    Sorry Ed, Tom is fusing The Matter even further. ~> more below

    From: (ehsjr)
    Roy Q.T. wrote:
    I'm shocked to read that FireMan Tom would suggest that the NEC allows
    for a 15Amp device on a 20Amp protected circuit...It does Not Allow for
    that, & it is a violation albeit a mild one, but nevertheless improper &
    Not Recommended. All he's done is attack every reply i post here... and
    now he's just being ridiculous and harmful.He must think I'm some punk
    tech from his township., I've been doing Electrical Troubleshooting &
    Installations for over 30 years and seen plenty stupidity like that go
    unchecked because they believe in the " pros " that did it, and not in
    the letter of the codes and the wording of the specifications and
    experience.
    After all: He is a Fireman, he lives for the Sinister Fire to take hold
    of your property so he can do his job., didn't know he'd stoop to that
    level though to insure future work. What happened to Better Safe than
    Sorry ?
    Leave it alone; Get the proper sized Receptacle & Breaker for the new
    circuit you are running for your Air Conditioner. I'm through with
    this.......
    Roy
    Gee Roy, You responded to my post, which contained nothing of what Tom
    said, nor anything about the use of 15A receptacles on a 20 amp circuit.
    For the record, it is allowed in the NEC. Note that you must have more
    than one receptacle on the circuit.
    Ed

    The More 15 A Receptacles on the 20A Line the worse it is., let say you
    have 18.5 Amps Loaded on other 15A receptacles and you think Oh that's
    cool., then you're nitwit client/friend says what the hell and adds on
    an extesnsion cord with an outlet strip at the end with another 9-12
    amps load to it, what do you think will happen?

    They Are Not Permitted in the NEC, do not assume they do....from
    semantics.

    They strictly state that you do not use any underrated devices., all
    over the tome. ®
     
  11. ehsjr

    ehsjr Guest

    Roy, I read it from the NEC, I do not assume. A 15 ampere
    receptacle is most definitely permitted on a 20 ampere
    branch circuit that has two or more receptacles or outlets.
    See article 210.21 (B)(3) which states:
    "Where connected to a branch circuit supplying two or more
    receptacles or outlets, receptacle ratings shall conform to
    Table 210.21(B)(3), or where larger than 50 amperes, the
    receptacle rating shall not be less than the branch-circuit
    rating."
    Table 210.21(B)(3) gives the receptacle rating for a
    20 ampere branch circuit as 15 or 20.

    It is not semantics - it is clearly stated in the NEC.

    Ed
     
  12. Roy Q.T.

    Roy Q.T. Guest

    From: (ehsjr)
    Roy Q.T. wrote:
    Gee Roy, You responded to my post, which contained nothing of what Tom
    said, nor anything about the use of 15A receptacles on a 20 amp circuit.
    For the record, it is allowed in the NEC. Note that you must have more
    than one receptacle on the circuit.
    Ed
    The More 15 A Receptacles on the 20A Line the worse it is., let say you
    have 18.5 Amps Loaded on other 15A receptacles and you think Oh that's
    cool., then you're nitwit client/friend says what the hell and adds on
    an extesnsion cord with an outlet strip at the end with another 9-12
    amps load to it, what do you think will happen?
    They Are Not Permitted in the NEC, do not assume they do....from
    semantics.
    Roy, I read it from the NEC, I do not assume. A 15 ampere receptacle is
    most definitely permitted on a 20 ampere branch circuit that has two or
    more receptacles or outlets. See article 210.21 (B)(3) which states:
    "Where connected to a branch circuit supplying two or more receptacles
    or outlets, receptacle ratings shall conform to Table 210.21(B)(3), or
    where larger than 50 amperes, the receptacle rating shall not be less
    than the branch-circuit rating."
    Table 210.21(B)(3) gives the receptacle rating for a 20 ampere branch
    circuit as 15 or 20.
    It is not semantics - it is clearly stated in the NEC.
    Ed



    Ed you know there are 3 ways to interpret what you read and mentioned
    here.,
    " Your Way ", Then, "My Way" & " The Correct Way "., as you mentioned:
    Check Out NEC Table 210.21(B) (3) Again where it's clearly specified

    Circuit Rating Receptacle Rating
    15 Not Over 15
    20 15 or 20
    30 30
    40 40 or 50
    50 50

    Now That Is Big Time BS & shaving Off Accuracy, and left to And, If &
    Or. as you may deduce below.

    NOTE {{{The case I mentioned Was a Real LIfe Browned/Melted 15 A
    Receptacle on a 20 Amp Circuit }}}

    * From Table 210.21(B)(2) you can clearly see that a load over 16 Amps
    Requires a 20Amp Receptacle, minimum.


    All I'm Saying is: Why Fiddle with the Numbers and go with a Lesser
    Circuit Ready Device, if you're wiring for 20A go with the Like Rated
    Products.

    Roy
     
  13. Roy Q.T.

    Roy Q.T. Guest

    NEC 210.21 [(B)(1)] ~ Receptacles: A single receptacle installed on an
    individual branch circuit shall have an ampere rating "not less" than
    that of the branch circuit.
    ®oy

    From:
    On 8 Jun 2005 04:21:48 GMT, wrote:
    It could just be that I can't find the part of the code that says a 15
    amp circuit cannot have a 20 amp receptacle
    Look at 210.21(B)(3) again. The top line says 15a circuits shall have
    receptacles "not over 15a"
     
  14. Roy Q.T.

    Roy Q.T. Guest

    Ref.: Table 210.21 (B) (2)

    Basically: All Sales, Installations & Hardware Destruction aside, & from
    a Purely Scientific Stand Point ~ I think Someone Goofed Up on that
    Section of Code.

    Experience is a Far Greater Teacher than Books alone.

    Roy Q.T.
     
  15. John Gilmer

    John Gilmer Guest

    Why?

    The goal was/is to reduce the need ofr extension cords. Having a string
    of outlets relatively close together on one circuit doesn't mean that each
    outlet can (at the same time) provide 15/20 amps but that, generally, you
    don't have to run an extension cord for the lamp, or whatever.

    The same idea is behind requirements for outlets at windows in store fronts
    and for GFCI outlets outside.

    IF someone has the need for heavy drawing appliances (Air Conditioners, room
    heaters, whatever) then you bump up against the overall protection for the
    circuit. If everyhing in a room is on the same string, there is no
    incentive to run an extension cord.
    Yeah. But in this case, all "experience" can do beyond the code is make
    you put in more than one circuit in your living room. And then your
    "experience" has to tell you how to demark when one circuit's outlets are
    and where the other one is. AND you have now created an incentive for
    running extension cords if there are TWO heavy loads in one corner.
     
  16. Roy Q.T.

    Roy Q.T. Guest

    From: (John Gilmer)
    Ref.: Table 210.21 (B) (2)
    Basically: All Sales, Installations & Hardware Destruction aside, & from
    a Purely Scientific Stand Point ~ I think Someone Goofed Up on that
    Section of Code.
    Why?
    The goal was/is to reduce the need for extension cords.   Having a
    string of outlets relatively close together on one circuit doesn't mean
    that each outlet can (at the same time) provide 15/20 amps but that,
    generally, you don't have to run an extension cord for the lamp, or
    whatever.
    The same idea is behind requirements for outlets at windows in store
    fronts and for GFCI outlets outside.
    IF someone has the need for heavy drawing appliances (Air Conditioners,
    room heaters, whatever) then you bump up against the overall protection
    for the circuit.   If everyhing in a room is on the same string, there
    is no incentive to run an extension cord.
    Experience is a Far Greater Teacher than Books alone.
    Yeah.   But in this case, all "experience" can do beyond the code is
    make you put in more than one circuit in your living room.   And then
    your "experience" has to tell you how to demark when one circuit's
    outlets are and where the other one is. AND you have now created an
    incentive for running extension cords if there are TWO heavy loads in
    one corner.

    *** I've suggested nothing of the sort***

    You asked me " Why ? " Let me answer :
    Living Room and AC outlets are not the sum of Receptacle Use., The case
    I mentioned was a Commercial Location ~>Backwall to Counters~> had
    several outlets all fully duped with plugs one had melted the plug on
    the extension cord and had signs of browning along the slots }:-o
    {I wired a seperate circuit for the display/counters and added 20A rate
    receptacles and circuits wiring to panel & breakers}=[@ a CellPhone
    Outlet] {used charges and fans alot.... despite of AC}

    Now if I had taken the General Consensus on Receptacles Discussed Here,
    I would have been troubled & felt negligent of my observations.

    If anyone is giving insentives out it's those that post Images of how
    wrong it is to do better than code work.

    Code Case Senarios are Basic, Minimum & Proper Safety Requirement Rules,
    in this case meeting codes is easy., Analyzing & Preparing a Circuit for
    Long Term Functionality, Safety & Versatility isn't.

    Experience said nothing else here but; To use Rated & Properly Selected
    Materials where you will not be supervising or controling the use of
    your work thereafter & in the years to come.... ®oy
     
  17. ehsjr

    ehsjr Guest

    Hi Roy,

    There is *no* interpretation. Listed 15 and 20 ampere
    receptacles are identical with the exception of the T slot.
    A 15 A receptacle will handle the current the same as a
    20 A receptacle. The copper, dimensions, material etc. are
    all the same, with the exception of the T slot.

    Your receptacle did not melt because it was rated 15
    vs 20. I've had to replace burned/melted 20 amp
    receptacles on 20 amp branch circuits. It's the use/abuse
    and age of the receptacle that causes failure, not the
    rating.
    It says that the *maximum* load is 16 amps, not *over* 16
    amps. Remember the 80% rule. 210.23(A)(1)
    Equipment manufacturers of cord and plug connected equipment
    requiring over 12 amps must use a plug that mates with a
    NEMA-5 20 receptacle or equivalent. That means the flat blades
    of the plug must be at 90 degrees to one another. Such a plug
    cannot fit into a 15 A receptacle.
    You are not fiddling with the numbers. Listed receptacles rated
    at 15 A or 20 A have identical current carrying specifications.

    Ed
     
  18. NRen2k5

    NRen2k5 Guest

    No. The NEC, and likewise the UL and the CEC, do not *always* "err on the
    side of caution". They mostly set practical, generally very safe conventions.

    - NRen2k5
     
  19. Roy Q.T.

    Roy Q.T. Guest

    You guys are Bizarre, too inquisitive & argumentative.

    my rebuttal:

    Even if i agreed with the lot of you on each of your noted points, you'd
    still think I have a problem understanding this Post or it's Merits and
    Solutions.

    With that in mind, The Hell with It.,

    I didn't come here to argue over Picky Ninny Engineering Standards that
    don't have apparent reason for excising but to arrange arguments over
    everything and anything Electrical that is Manufactured.
    Some No-Code Literate people think they do the dandiest things with
    plugs and receptacles regardless of the NEC or these arguements.

    It's either the Best Solution or I leave it alone.... Teachers think
    different from most of you and I don't care., but you told them what &
    how you want it & how you made it., not the other way around, You are
    All Confusing and wrong about me somehow. I'd swear right back today
    }:p

    Since my expertise is Technical., you just keep giving us the best
    designs possible for the best Installation/assembly possible.


    And Phil; don't harass me any more over what you think I don't
    understand, I am not dumb, didn't I spell it out with positive
    assertion?, some of you are damn near insulting and inhospitable like in
    here ...
    some of you are cool, others perhaps just confused about my assertions.
    Roy ~ E.E. Tech
     
  20. ehsjr

    ehsjr Guest

    I would agree with the interpretation of 210.21(B)(3)as
    applicable. The NEC language is a little different with
    regard to "outlets" and "receptacle". Although people often
    refer to a receptacle as an outlet, they are treated as two
    different things in the NEC.

    Here's three definitions from the NEC:
    "Outlet. A point on the wiring system at which current is taken
    to supply utilization equipment."

    "Receptacle. A receptacle is a contact device installed at the
    outlet for the connection of an attachment plug. A single
    receptacle is a single contact device with no other contact
    device on the same yoke. A multiple receptacle is two or more
    contact devices on the same yoke."

    "Receptacle Outlet. An outlet where one or more receptacles
    are installed."

    Ed
     
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