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  1. #14
    Quote Originally Posted by jpsmith1cm View Post
    The logic of believing a "rule-of-thumb" given to residential AC techs and trying to apply it to something he doesn't know anything about.


    what PHM said.

    A common practice during pumpdowns is to push the contactor in with a screwdriver. This, of course, cannot be applied to a part winding start motor. The control must be bypassed to bring both contactors on.


    I must say that I have never seen a part winding start motor used on a rack system. A few on AC equipment, but not on the racks.

    will holding in one contactor just burn out?

  2. #15
    Join Date
    Sep 2002
    Posts
    12,438

    yes

    Yes it will.

    Normally if this happened; timing or contactor failure, the overloads would protect the motor. But holding one contactor in manually eliminates that O/L safety function.

    PHM
    ------






    Quote Originally Posted by Friget_Sparrky View Post
    will holding in one contactor just burn out?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  3. #16
    Join Date
    Sep 2007
    Location
    Boise, ID
    Posts
    4,270
    I'm sure I am not the only one that remembers chillers that ran in a vacuum. Probably still some out there.
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  4. #17
    Join Date
    Sep 2002
    Posts
    12,438

    A/C or refrigeration?

    Do mean for A/C or refrigeration applications?

    PHM
    ------




    Quote Originally Posted by Gib's Son View Post
    I'm sure I am not the only one that remembers chillers that ran in a vacuum. Probably still some out there.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #18
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,659
    Quote Originally Posted by Gib's Son View Post
    I'm sure I am not the only one that remembers chillers that ran in a vacuum. Probably still some out there.
    Yep.

    Low pressure equipment is still out there.

    That wasn't quite what I was referring to, though.

    I've got more than a couple of pieces of equipment running between 1 and 10# suction pressure and I consider that to be quite normal.

    R-12 low temp and R-22 low temp have to run very low suction pressures in order to hold temp.

  6. #19
    Join Date
    Mar 2007
    Posts
    3,108
    Yes there's a ton of low-pressure chillers out there. New ones are being installed and started up every day.

    I'd never advocate pushing in a motor starter or contactor, and definitely not two contactors at the same time. Part-winding starters are there for a reason, and they are usually applied on large HP compressors and motors. I don't want a screwdriver being the only thing between my hand and 460volts/200+amps.
    "There is no greater inequality than the equal treatment of unequals."

    -Thomas Jefferson

  7. #20
    Join Date
    Oct 2011
    Location
    La.
    Posts
    281
    This is the problem when residential service techs start to work on larger equipment. I will never push a contactor in by hand. I have seen the outcome of it and you can not do that in a safe manner. I have gone behind other service techs that were severly burned on their hands and had to have metal removed from their eyes because of this practice. Take the time to do the job safe and be able to show up tomorrow to work again. GOOGLE ARC FLASH VIDEOS AND YOU WILL THINK TWICE ABOUT HURRYING IN THE FUTURE!!

  8. #21
    Join Date
    Feb 2004
    Location
    British Columbia, Canada
    Posts
    521
    Yup. As I saw on a poster once, "ELECTRICITY IS A VENGEFUL B***H, NOT TO BE TRIFLED WITH".
    The one time that you run across a dead short or a like problem in a motor, as you make the contact at the contactor...that can change your life. For that matter, how many of us are religious about wearing eye protection? I wish I could say that I never forget to put them on. Burnt hands would be bad but not comparable to losing your sight.

  9. #22
    Join Date
    Sep 2006
    Location
    River Forest IL
    Posts
    70

    A-men on the Arcflash

    Everyone in this trade-field AND office-should have to go through arcflash training. Heck-I think everyone should have at the minimum OSHA 10 training. Lots of ways to get hurt/killed. Field personnel need to know the risks and how to avoid them, office personnel need to know the same so they know better than to question the field when it comes to safety concerns. We've all been there though, take a shortcut 'cause we want to get in/out-I'm as guilty as any. I had an apprentice question not too long ago me on why I was checking power in to a unit after I had shut the disconnect off. I told him (1.) a disconnect is a switch, and all switches eventually fail, and (2.) Had I not checked it and it was bad-it wouldn't have been the first time I got shocked, but it could have been the last.

  10. #23
    Join Date
    Feb 2004
    Location
    British Columbia, Canada
    Posts
    521
    [QUOTE=will smith I had an apprentice question not too long ago me on why I was checking power in to a unit after I had shut the disconnect off. I told him (1.) a disconnect is a switch, and all switches eventually fail, and (2.) Had I not checked it and it was bad-it wouldn't have been the first time I got shocked, but it could have been the last.[/QUOTE]

    Three weeks ago I was changing out a burnt stepdown transformer. I hit the disco only to find the switch had failed on the middle leg. Never saw that before, heard about it but never had it happen to me. You can't check for power too carefully.

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