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Thread: Indoor unit

  1. #41
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    Quote Originally Posted by MAC702 View Post
    Again, I've no need to find out. I'm not saying that to be rude, just admitting that I'm not an expert at that part of the Code because I already know that every 120V machine I've ever seen (up to 5-tons, with a 3/4 HP blower) is already on a dedicated 15A breaker, #14 wire, and either a NEMA 5-15 receptacle or 15A switch. I work on these machines for a living, and see different ones every day, residential and commercial.

    .
    Question: I thought at the beginning this was just an air handler like the inside unit of a heat pump, but it is a gas furnace instead. I am guessing the AC coil in part of this unit, not that matters here.

    Would not there be a nameplate on the unit with MCA and MOCP given?

    As you mentioned for disconnecting means:

    If these units are cord connected, the receptacle works.

    If hard wired, a switch is prolly used, although I have gotten leery of using snap switches in many cases.

    The HP ratings are a lot lower than one expects. I like the el cheapo pull out discos for less than $10. 60A and 10HP rating, I know it works.
    "Electricity is really just organized lightning." George Carlin


    Derek

  2. #42
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    Quote Originally Posted by jumper View Post
    Question: I thought at the beginning this was just an air handler like the inside unit of a heat pump, but it is a gas furnace instead. I am guessing the AC coil in part of this unit, not that matters here.

    Would not there be a nameplate on the unit with MCA and MOCP given?

    As you mentioned for disconnecting means:

    If these units are cord connected, the receptacle works.

    If hard wired, a switch is prolly used, although I have gotten leery of using snap switches in many cases.

    The HP ratings are a lot lower than one expects. I like the el cheapo pull out discos for less than $10. 60A and 10HP rating, I know it works.
    Can be, but often is not. If there were a hermetic compressor installed in it there would be both on the nameplate.I think that is part of listing requirements, but without a compressor they often just have a very simple amp rating and nobody ever knows exactly what it is based on either. Units usually have the blower plus a combustion draft blower and 24 VAC controls but never break down the load details. May or may not have a refrigeration coil, but if compressor is in a separate unit it is not something subject to art 440.

  3. #43
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    Quote Originally Posted by jumper View Post
    Question: I thought at the beginning this was just an air handler like the inside unit of a heat pump, but it is a gas furnace instead. I am guessing the AC coil in part of this unit, not that matters here....
    A gas furnace variant of an air handler adds extremely little to the load: just a small draft-inducer motor and the controls. The AC coil just sits there in the air stream, and is usually field-installed as a separate box, often made by a different manufacturer.

  4. #44
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    Quote Originally Posted by MAC702 View Post
    A gas furnace variant of an air handler adds extremely little to the load: just a small draft-inducer motor and the controls. The AC coil just sits there in the air stream, and is usually field-installed as a separate box, often made by a different manufacturer.
    I only mentioned the AC coil as a passing remark, mostly to myself. OP remarked about the outside condensing unit and it popped into my head.

    I did not mean to add it to conversation, it was basically an aside.

    As kwired noted though, these units seem to be not marked with MCA and MOCP. I find that odd.

    As someone else commented that 440 would not really apply and I agree.

    430 covers motors, but it really falls into 420 as an appliance lt seems. I think that was proposed earlier and I would prolly go that way also.

    If you had not installed these before, what would be your direction of thought?
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #45
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    Art 100:
    Appliance.


    Utilization equipment, generally other than industrial, that is normally built in standardized sizes or types and is installed or connected as a unit to perform one or more functions such as clothes washing, air-conditioning, food mixing, deep frying, and so forth.
    422.3 Other Articles.
    The requirements of Article 430 shall apply to the installation of motor-operated appliances, and the requirements of Article 440 shall apply to the installation of appliances containing a hermetic refrigerant motor-compressor(s), except as specifically amended in this article.
    The furnace is a motor operated appliance, if a unit has a hermetic compressor it falls under art 440.

    422 could specifically amend general items mentioned in 430 or 440 on some appliances.

  6. #46
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    I'm usually only looking for the data labels to get a model and serial number. So I went through my phone where I have a few pics of some to look at them. All the furnace and air handlers that I have pics of have the MCA and MOCD info listed on the label. They are usually 10-12 and 15, respectively.

    This label is often on the INSIDE of a service panel.

    In looking at a few random Google Images of furnace data labels, I see some that only have an MCA.

  7. #47
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    Quote Originally Posted by kwired View Post
    Art 100:


    422.3 Other Articles.


    The furnace is a motor operated appliance, if a unit has a hermetic compressor it falls under art 440.

    422 could specifically amend general items mentioned in 430 or 440 on some appliances.
    It is split system unit so it has compressor in outdoor condenser which is used for outdoor air condioner purpose however for indoor heat it uses gas furnance and the ducts have fans. For the fans 0.75 hp 120v I trying to size disconnect and circuit breaker.


    So i am not sure if unit as a whole would use the compressor i.e. hemratic motor.

    Do any of you know of accurate sizing calculator or excel spreadsheet that you all use for sizing hvac, motors, appliance circuit breakers, fuse, and disconnects?

    Sent from my SM-G935U using Tapatalk

  8. #48
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    Quote Originally Posted by codequestion View Post
    It is split system unit so it has compressor in outdoor condenser which is used for outdoor air condioner purpose however for indoor heat it uses gas furnance and the ducts have fans. For the fans 0.75 hp 120v I trying to size disconnect and circuit breaker.


    So i am not sure if unit as a whole would use the compressor i.e. hemratic motor.

    Do any of you know of accurate sizing calculator or excel spreadsheet that you all use for sizing hvac, motors, appliance circuit breakers, fuse, and disconnects?

    Sent from my SM-G935U using Tapatalk
    What is controlling these fan motors?
    I find it hard to believe that this indoor unit doesn't have some type of thermostatically controlled device that controls the on and off time of the blower unit itself.

    JAP>

  9. #49
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    Quote Originally Posted by codequestion View Post
    ... the ducts have fans. For the fans 0.75 hp 120v I trying to size disconnect and circuit breaker.

    So i am not sure if unit as a whole would use the compressor i.e. hemratic motor. ...
    This is new information, unless I missed something. You have fans (plural) in the ducts? That's not something you see every day, but they are out there. They won't be 3/4 HP.

    Why does the hermetic compressor keep coming into this discussion? A split-system has that in the outdoor unit which is on its own dedicated 2-pole circuit.

    Have you been able to walk a job and see how these are installed?

  10. #50
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    Quote Originally Posted by MAC702 View Post
    This is new information, unless I missed something. You have fans (plural) in the ducts? That's not something you see every day, but they are out there. They won't be 3/4 HP.

    Why does the hermetic compressor keep coming into this discussion? A split-system has that in the outdoor unit which is on its own dedicated 2-pole circuit.

    Have you been able to walk a job and see how these are installed?
    That's correct.
    We don't have all of the information yet.

    Still need to know if these are independent motors at random locations spread throughout the duct work, or , if they are interconnected to the blower unit controls somehow.

    JAP>

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