A/C Condenser and Air Handler

Discussion in 'Electrical Forum discussion & Blog' started by seaneys, Nov 27, 2008.

  1. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Hello,

    I'm running the power to our new a/c air handler (attic with pull down stair) and condenser (outside). The work will be inspected and is permitted.

    Both the compressor and air handler are 220v. The compressor requires 30A min. The air handler requires 15A min. I was a little surprised that the air handler is 220v.

    I hate to take up 4 positions in my panel for the both the compressor and air handler. To minimize the number of breaker positions required, I'm considering putting in a 50A 220v breaker in the panel to cover both the air handler and the compressor. To do this I would also need locate a 30A (fuse) panel at the compressor and a 15A (breaker) panel at the air handler.

    If I have read the NEC correctly, I can use 6ga THHN stranded copper for the lines to the compressor and air handler. I believe I also need 1 1/4 conduit (this seems large). I plan to pull a ground wire with the conduit to be conservative.

    Does this seem like a reasonable solution? Would I be better off just biting the bullet and adding a subpanel in the basement if I need it later? 50A at 220V is a little scarey, but it will be in conduit...

    Thanks!
    Steve
  2. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,005
    Location:
    NY State, USA
    You would be dealing with tap conductors and several other code issues doing it that way. Plus adding considerable cost.
    Even installing a sub-panel. Is it worth that much extra cost to save to breaker spaces???

    If so then a sub-panel right near the main is your best bet to get more breaker space. This way you are not just adding space for this project. You will have space for later as well.
  3. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    There is not enough information for anyone to give you any guidance and what you are proposing to do is completely illegal.

    You will need to use up 4 spaces in your main panel unless you plan on installing a sub panel.

    We need to know the size of your service, FLA rating of the compressor motor, Nameplate rating of the both the compressor(condensing fan unit) and furnace, (is there an FLS on the fan motor too) What code cycle you are under and a few more items.

    There is a lot more to this than people realize.
  4. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    I may misusing my terminology here, but I believe it is accurate to call the two separate panels 'sub panels'. The panels would be fed from a single 220v 50Amp breaker in my main panel. I would need to pull the neutral, two 220v legs, and a ground line. The compressor panel has a single fuse. The air handler has a double breaker.

    My service is 200Amps, BUT my plans are to feed this through the 50A breaker in the main panel. The current draw would be limited by the 200 A main breaker.

    I can get the name plate on the compressor indicates 30 A min service. The name plate on the air handler indicates 15 A min service. We do not have an air handler for our furnace (radiant heat).

    I'm thinking I should just use 4 slots in the main panel and put in a subpanel later if needed. One item that is filling the panel is the new requirement in my area for arc detect breakers.

    We're under the 2005 NEC.

    Thanks again!
    Steve
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,565
    Location:
    North Carolina
    If you are planning on installing a 50 amp circuit to feed both where will this 50 amp circuit stop. From the stopping point of the 50 amp circuit Section 240.21 will mandate the installation for the tap conductors. These taps will need to land in a disconnect that has overcurrent protection no larger than the tap conductor.

    This installation will require that you buy two “subpanels†so to speak as the tap conductors will be required to land on an overcurrent device not larger than the ampacity of the conductors.

    (1) Taps Not over 3 m (10 ft) Long. Where the length of the tap conductors does not exceed 3 m (10 ft) and the tap conductors comply with all of the following:
    (1) The ampacity of the tap conductors is
    a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
    b. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
    (2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
    (3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
    (4) For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.

    (2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:
    (1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.
    (2) The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.
    (3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.


    In order to save your self some money and a lot of grief just hire an electrician and have no worries.
  6. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Excellent description of the problem by jw.

    If I may try to summarize in lay terms:

    There are legal and practical reasons NOT to do what you want. The installation instructions for each of those units probably specifies a dedicated circuit. Overall, it is probably much easier to install a dedicated subpanel, and then each device can have its own breaker. The subpanel could be right adjacent to your existing main panel.

    Air handlers are routinely available in many configurations, including options for 120 volt, and in your case 240 volts. If you are not using electric heat strips in your air handler, you could have simplified your install by specifying a 120 volt air handler.
  7. maintenanceguy

    maintenanceguy In the Trades

    Messages:
    107
    Location:
    Pennsylvania
    It seems like a complicated way to do it but I don't see a violation.

    I'm assuming you've got your breaker sizes correct since I can't see the nameplates from here.

    If he runs #6 from his 2 pole 50A breaker and then to a junction box where he splits the circuit. One branch from the JB goes to a breaker or fuses appropriate for the air handler in the attic and one branch goes to a breaker or fuses sized correctly for the condenser outside. I think this works just fine.

    I don't see where tap rules come into effect.
  8. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT

    Read post #5.
  9. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    Just run two circuits from the main panel.

    If you insist on running them on one 50, install a 50A, 4 space sub panel at the condenser and feed the AH from there. The breaker will act as a disconect for the condenser. The AH will need it's own means of disconnect.
  10. Johnny C

    Johnny C Electrician

    Messages:
    23
    Location:
    Mass. & now Virginia Beach, VA
    AC condenser and air-handling unit.

    This answer is based on the 2005 NEC.
    Secton 110.3(B) requires you to follow the listing and labeled installation instructions applicable to that particular unit. The instructions and namplate should provide the minimum conductor size, the maximum fuse or circuit breaker size, and if the breaker must be of the HACR type. The instructions for the rating of fuses and circuit breaker required to provide ground-fault and short-circuit protection are based on Section 440.21, 440.22, and 440.31.
    In order to provide the proper protection of the branch-circuit conductors and the associated utilization equipment and be in accordance with the NEC, it is smart to run two branch-circuits protected by their own fuses or CB's.
  11. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Okay.. I've definitely decided to just add a second 220V 15A breaker in the panel. If I ever need to add a subpanel it will be much easier to locate one at the panel. I really wish the HVAC sub had installed a 110V unit.

    The main reason I didn't hire a pro to just finish the job is that I am wiring the rest of the addition myself. I need to complete my work and get it inspected before I call in a professional. We added the A/C to the original project. A pro from the neighborhood helped with a service entrance change, but at the end of the day I am officially listed on the permit.

    Steve
  12. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,005
    Location:
    NY State, USA
    Since when? I have NEVER seen this with HVAC equipment. About the only time I have seen a conductor size mentioned is with a spa.
  13. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    I checked in the snow.

    The compressor does not have the wire size required. It does have the information required to size it.

    Steve
  14. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,005
    Location:
    NY State, USA
    Exactly......
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Forum Title Date
Electrical Forum discussion & Blog A/C condenser hook-up Aug 16, 2007

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