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    Wiring size controversy (9 Posts)

  • Flounder1310 Flounder1310 @ 12:58 PM
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    Wiring size controversy

    What size wire is required for an American Standard HP 7.5 ton 3 phase 208 volt airhandler which tag marked in red says 90 amps. Would love to run MC cable for feed if at all possible. Air Handler has heat strips installed. Installer marked tag for 90 amp. This is all info I have available.
  • JStar JStar @ 1:02 PM
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    Wire

    How long is the run of wire from breaker to unit?
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  • RJ RJ @ 1:19 PM
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    wire

    Some installs will require  separate wiring and disconnect for the heat strips, check the codes in your area. Also are you figuring a compressor and a evap motor   whats the total horsepower and KW
    RJ
  • Flounder1310 Flounder1310 @ 3:49 PM
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    Wire

    First of all thanks! I have only talked and not seen the setup but I did ask for all the info that you have ask! The run from breaker to unit is 20-25 ft. The condenser will be feed from a different sub panel. So only the heatstrips and IDF will be involved. I will go to where the units are and get model # of AH if I need to. The friend who ask told me the tag on the unit was circled in red and ask me what size wire.
  • Flounder1310 Flounder1310 @ 4:04 PM
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    Wire

    I am in NC and do service work but no install. The AS units only require one disconnect on most of their units. Breaker to HS bank is built in on the units if they are factory installeHS. I feel sure these are without looking because of installer circling the 90 amp model # on the factory tag. If I need more info please let me know, I will go to site and get all necessary info for y'all. Thanks again. I will say this is a church sanctuary and the men are trying to do all the work themselves. They have some knowledge of the electrical but this has them stumped! The units however were installed by a local company but they don't seem to know either. They installed to drawing specs. I don't know what's going on!
    This post was edited by an admin on May 4, 2014 4:10 PM.
  • Jamie Hall Jamie Hall @ 4:42 PM
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    90 amps?

    My friend,, you are no longer playing with marbles.

    First, double check the nameplate amperage draw.  Then check to see if there are, in fact, any built in breakers on the unit.  Assuming that it all adds up to 90 amps...

    Now.  You will need a separate, fused or breakered disconnect on you main switchboard to handle this thing.  It will have three poles on the breaker, or three fuses.  If it has fuses, it will also have a disconnect switch (three poles).  You  may be able to find a 90 amp disconnect, but I'm going to bet you're going to find a 100 amp unit.  That will work -- if there is a breaker in the unit itself.  If not, and it says 90 amps, it means 90 amps, and you'll have to find that.

    The wires from the unit to the disconnect will be No. 2 copper.

    If there is a separate neutral terminal on the unit -- there may well be -- it will need a separate No. 2 wire in addition to the three phase wires.  This will go to the disconnect, but does NOT, repeat NOT, have a switch, fuse, or breaker on it of any kind.
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Flounder1310 Flounder1310 @ 6:43 PM
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    Wire

    Thanks Jamie! I believe my best advice to my friend is to contact an electrician with commercial experience. I will go take a look at the setup,do as little figuring but I know this is out of my league. The good news is my son is a general contractor and will know exactly who they can call. Thanks everyone and I think I will put this one to bed! :)
  • Jamie Hall Jamie Hall @ 7:52 PM
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    Wise man...

    There is a time and place for everything -- but wiring 90 amp circuits really is a job for a pro!
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Techman Techman @ 7:51 PM
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    Wire sizing

    A 71/2 hp motor, 3ph, 208v draws about 22-25 amps. So that rating of 90a is more than likely for the electric heat. The AirHandler name plate should have the motor running amps, locked rotor amps and the" minimum circuit ampacity rating". The mfrg tells you the amps and you wire accordingly. Does this AH nave a disconnect or how about a "starter"? You mentioned 208v , with electric heat , that lower voltage changes the BTU/amps of the heater.
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