Rotation Sensitivity
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  1. #1
    Join Date
    Aug 2004
    Location
    Bentonville, AR
    Posts
    4

    Question

    Hello, I am a commercial electrician and was wondering about the rotation sensitivity of any type of HVAC equipment. We all know that with any type of equipment that is 3-phase, some motors can be damaged if the phase is backwards... or if any leg of a phase is missing. My question is, do most newer Air Conditioners, Heat Pumps, etc. have an auto shut-off if they detect the phase is backwards or a leg is missing? A few days ago, one of our transformers took a major lighting strike and blew out the A-Phase, well that was over the weekend, we came back to work on Monday and the AC units were acting goofy. The HVAC tech wasn't positive if they had saftey shutoffs on them or not, how funny. I am just wondering since the guy couldn't answer my question.

    Thanks,

    Paul

  2. #2
    Join Date
    Aug 2004
    Location
    Maryland
    Posts
    62
    Unless the unit was purchased with a phase monitor or one was installed in the unit when the unit was installed then no there is no type of protection. The compressors will go off on internal overload (scroll or screw compressors) but by tht time the damage has already been done. They can run for only a few seconds with out damaging them if the rotation is incorrect.

  3. #3
    Join Date
    Dec 2003
    Location
    45th Parallel
    Posts
    954
    Depends. Just the answer you were lookin for, right.
    It depends on what the engineer spec.d and what the owner wanted to spend. Also depends on the size of the unit, a residential size unit wouldn't have a phase monitor, but larger commercial equip sometimes does.
    It can easily be added as you know.
    The HVAC tech may not have been familiar with that equip. IF he works on your equip regularly he should have known.

    Most units will trip the breaker, or blow the fuses, when single phased. Assuming they have been sized properly.


  4. #4
    Join Date
    Aug 2004
    Location
    Bentonville, AR
    Posts
    4
    Alright, I was afraid of that. The HVAC Tech should be coming out again this monday to look at it. Now the question is who pays for it. The tech said since it isn't our fault or their fault, they will probably be able to get a replacement for free acting like it was a defect. However, he isn't even positive it is damaged, all we know is since the storm, the electronic thermostat will not go out of test mode, even whit the key sequences he had us enter. He is almost 100% positive that the storm blew out the thermostat and the unit is still alright. I guess we will hope for that.

    Thanks again everyone,

    Paul

  5. #5
    Join Date
    Sep 2002
    Posts
    1,389

    Paul

    It really wouldn't have mattered if there was phase or over-voltage protection. The lightening not only intensifies the primary thus creating a high secondary voltage on the 24V. circuits but the lightening also uses its DC current to go to ground through the building electrical circuits. That ruins electronic equipment. It can happen so fast and the power so powerful that no device can stop it fast enough as the protive devices are, at the same time, receiving this larger voltage. The power company or the building owner's insurance policy may offer some relief if the total cost is worth exploring.
    The big question after such an episode is: did the building phasing stay the same after all was finished or are all 3-phase equipment now running in the opposite direction. That can cause future chaos.

  6. #6
    Join Date
    Dec 2003
    Location
    Nevada
    Posts
    1,815

    Re: Paul

    Originally posted by twcpipes
    The big question after such an episode is: did the building phasing stay the same after all was finished or are all 3-phase equipment now running in the opposite direction. That can cause future chaos.
    Check this. The phase protection is usually an option.
    Quote
    “Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams

    "We can't solve problems by using the same kind of thinking we used when we created them."
    Albert Einstein

  7. #7
    Join Date
    Oct 2001
    Posts
    6,940
    have them check the other 3 phase equipment in the building exhaust fans,pumps,elevator operation,then up at the unit with 3 phase powered push a condenser fan in for rotaion check then the supply fan.check all your secondary voltages9within units)and ring out all the T sides of the compressor contactors to ground and between the 3 windings.disconnect the stat wires on the rooftop and run it from jumps on the 24v board verify starts and any noises from motors or compressors.refeed the 24volts to the stat and then work on that..pull the stats off the subbases(verify 24v)and jump the system from the subbasesR,G...to Y ,then R to W for heat with somebody up top telling you what is cycling..then re-install the stats

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