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Thread: Mini Splits

  1. #11
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    Jul 2003
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    Quote Originally Posted by kwired View Post
    The motor may be a DC motor but the question about a typical AC toggle switch not being rated for DC becomes a question of whether it is interrupting DC or not. If the rectifier is in the outdoor unit then it is wrong to use a switch only rated for AC. I don't know enough about what is typical for these units to know where the rectifier is located.
    I would find it odd that the switch would actually be disconnecting only the portion of the circuit that's DC and not some AC component upstream from the motor.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  2. #12
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    Apr 2003
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    Fort Collins, Colorado
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    I have a mini split in my house, no inside disconnect.
    I don't require inside disconnects when I inspect them. Right or wrong,homeowners would hate them.
    Ron

  3. #13
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    Jan 2007
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    Quote Originally Posted by rcarroll View Post
    I have a mini split in my house, no inside disconnect.
    I don't require inside disconnects when I inspect them. Right or wrong,homeowners would hate them.
    For Aesthetic reasons I take it?


    JAP>

  4. #14
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    Quote Originally Posted by jap View Post
    For Aesthetic reasons I take it?


    JAP>
    Yep
    Ron

  5. #15
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    Apr 2009
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    I have never seen a disconnect on a residential or commercial mini split on the inside. Take that with a grain of salt though as Virginia is still under the 2011 NEC for commercial, and a good number of these units could have been wired under the 2008 or even 2005 NEC.

    Are the DC motors even of a high enough voltage and amperage to cause an arc worrying about? Interesting is too vague a term... I find that light switches that Arc internally interesting... Some might find a bolted fault across 480 3-phase interesting, or a 500 KV transmission line opening in throwing a lightning bolt a hundred feet in the air interesting
    Electricians do it until it Hertz!

  6. #16
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    Dec 2007
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    Quote Originally Posted by JFletcher View Post
    I have never seen a disconnect on a residential or commercial mini split on the inside. Take that with a grain of salt though as Virginia is still under the 2011 NEC for commercial, and a good number of these units could have been wired under the 2008 or even 2005 NEC.

    Are the DC motors even of a high enough voltage and amperage to cause an arc worrying about? Interesting is too vague a term... I find that light switches that Arc internally interesting... Some might find a bolted fault across 480 3-phase interesting, or a 500 KV transmission line opening in throwing a lightning bolt a hundred feet in the air interesting
    High enough voltage is a good possibility. These units are usually 208-240 volts input - if directly rectified from input volts I'd say it is high enough to be a concern.
    I live for today, I'm just a day behind.

  7. #17
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    Jan 2007
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    Quote Originally Posted by JFletcher View Post
    I have never seen a disconnect on a residential or commercial mini split on the inside. Take that with a grain of salt though as Virginia is still under the 2011 NEC for commercial, and a good number of these units could have been wired under the 2008 or even 2005 NEC.

    Are the DC motors even of a high enough voltage and amperage to cause an arc worrying about? Interesting is too vague a term... I find that light switches that Arc internally interesting... Some might find a bolted fault across 480 3-phase interesting, or a 500 KV transmission line opening in throwing a lightning bolt a hundred feet in the air interesting
    I would agree.

    Also if it were a high enough DC voltage and current I wouldn't think a standard snap switch would be used for the disconnecting means to begin with.

    JAP>

  8. #18
    Join Date
    Apr 2017
    Location
    Boston, MA, USA
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    71
    Never liked the idea of having a 3 pole switch required for the indoor unit and always wondered:

    1. Is a 3 pole switch rated to have both ac and dc on the same yoke?
    2. Often times people install a plastic old work box next to the unit to accommodate the switch (metal ow is too narrow), but the switch didn't have a grounding screw, so the switch itself would not be grounded.
    3. Why is the requirement for a disconnect (i.e. padlockable device) for a wall oven hardly ever enforced, but was strictly enforced for mini splits? I realize we are talking about 2 different animals, 440 vs 422.
    4. Why the heck don't the manufacturers just put an on-off switch on the unit and call it a day?

    Glad to see this requirement go away.

  9. #19
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    Aug 2017
    Location
    Los Angeles CA
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    Actually many of these units use small VFD's on the compressor and possibly the fan motor although as small as these indoor fan is, it would seem a simple multi winding motor would be far more cost effective.

    The point is while a DC inverter may be inside the unit, the indoor unit disconnect still sees 120v or 240v AC. And a double pole should be fine as the third wire usually is low voltage control or data signal.

    There are a lot of myths about the indoor unit wiring. Such as you can't splice it, you can't use solid wire. Hogwash IMO as an EE. The data signals that go ever the control wire are low bandwidth and have to be immune from EMI anyway. There is no reason 12-14/3 NM, BX, AC can't be used for that. The expensive cables the manufactures sell is in no way specially shielded either that I have seen.

    I think these "special" cables are just a money grab from the unit manufacture. Of course they could void the warranty if you don't use them. Then comes the question of listing. Some of these OEM cables look like nothing more than foreign 14/4 SJT. Are these cables even listed for in-wall use under the NEC?

  10. #20
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    Quote Originally Posted by Andy Delle View Post
    Actually many of these units use small VFD's on the compressor and possibly the fan motor although as small as these indoor fan is, it would seem a simple multi winding motor would be far more cost effective.

    The point is while a DC inverter may be inside the unit, the indoor unit disconnect still sees 120v or 240v AC. And a double pole should be fine as the third wire usually is low voltage control or data signal.

    There are a lot of myths about the indoor unit wiring. Such as you can't splice it, you can't use solid wire. Hogwash IMO as an EE. The data signals that go ever the control wire are low bandwidth and have to be immune from EMI anyway. There is no reason 12-14/3 NM, BX, AC can't be used for that. The expensive cables the manufactures sell is in no way specially shielded either that I have seen.

    I think these "special" cables are just a money grab from the unit manufacture. Of course they could void the warranty if you don't use them. Then comes the question of listing. Some of these OEM cables look like nothing more than foreign 14/4 SJT. Are these cables even listed for in-wall use under the NEC?
    I am not sure this is accurate as many of these units are run with T-stat wire between the indoor and outdoor units. I have seen the line voltage units also and I agree that they are fine wired with 14/3 nm or whatever.... But some of these units are run with low voltage to the indoor unit
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