Page 2 of 2 FirstFirst 12
Results 14 to 20 of 20
  1. #14
    Join Date
    May 2004
    Location
    Salt Lake City/Tooele
    Posts
    5,054
    Post Likes
    Nice write up on that link by a guy who says he is "a know it all". Interesting how he says it is not as common indoors as it is outdoors and I never paid that much attention to when I diagnose it but I would have to agree. His pictures are not that good. I have one from a recent find that has a much more obvious carbon track.

    In the case of this system, it is 460v 3phase listed but running at around 490v respectively phase to phase. This is on a packaged chiller from the late 80's. This particular contactor is for one of the two semi-hermetic compressors. The chiller is located in a utility building on one side of the main building and the MCC box for this chiller is located in the electrical building on the other side of the main building. Found the L2 and L3 fuses in the MCC blown. I go back to the chiller and shut off and lock out that disconnect, go back to the MCC and ohm out everything to make sure it was not between the MCC and the chiller disconnect. Replace the fuses, close the MCC up and throw power back on there. Fuses held. Now back to the chiller and the disconnect, verify power on the line side of the disconnect. Open up the control cabinet of the chiller and visually inspect and immediately saw the blackened contacts of compressor A contactor. Further inspection could see the tale-tale sign of carbon tracking going from L2 to L3 or vice versa. This one was so obvious that I was able to get permission to take pictures.

    These buildings are remote so not until something happens or something is not working is when someone is called out, other than PM time. In this case I replaced the contactor and motor protector combo and double checked everything. I closed up the unit and power the unit back up. Instantly the contactor began to chatter loudly and rapidly. I shut back off the disconnect. This unit has a 120v single phase control circuit that is supplied by a transformer taking 460v to the 120v in the cabinet. The wire feeding to the liquid line solenoid had oh so slightly rubbed through against inside the MC cable sheath from nearly 40 years of vibration, it was small of a rub through that is was not enough to blow the fuse of the transformer but enough to cause a voltage drop. The contactor coil energizing and pulling in the contact was the needle that broke the camels back, it would pull in and could not hold dropping out the contactor, allowing voltage to regain and try again, dropping out again, over and over and over. This probably was going on for days for all I know but this rapid cycling of the contacts, in this case, is what quickly built up this fine specimen of carbon tracking.
    PS there was a bit of talk about contactor auxiliary switches in the PRO forum, the auxiliary seen on the contact here is to energize the remote condenser located on the roof.

    Should be three pictures of the same contactor, the close up shows a very obvious bridge of carbon that had built up and over the arc guard between the L2 and L3 Line side terminals. This little bit of carbon was what wiped out the main fuses in the MCC.
    Attached Images Attached Images    

  2. #15
    Join Date
    May 2004
    Location
    Salt Lake City/Tooele
    Posts
    5,054
    Post Likes
    Quote Originally Posted by Mustang8 View Post
    i seen some green color like copper oxidization on the contact inside glass relays...
    Only way you are getting copper oxidization inside that icepube relay is if moisture is or has been present.

    It never gets cold enough where I am at for long periods of time, but Lennox makes a burner compartment heater to prevent condensation from forming and rusting out the burners and creating moisture issues in the control cabinet, usually says for Canada Only in the old engineering manuals, never understood that, gets pretty damn cold in the Northern United States too, must be a magic border thing....Any hooo, stay with me on this, air trapped inside the cube relays during off cycle is cold, when the pube relay is energized, the coil inside that relay warms up causing the cold air trapped inside the relay box to be warmed by the coil and in turn it condenses. You see the signs of the that with the greening oxidization of the copper in that relay, with 575v who knows what else that condensate helps spawn, too.
    Attached Images Attached Images  

  3. #16
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    29,714
    Post Likes
    Quote Originally Posted by Mustang8 View Post
    i dont have any experience with carbon tracking .. how to diagnose it, if it cant be found with meter??
    feels like temps was even worst at a time...
    I can post some pictures later....but typically what I see is visible arc damage between the connectors staked on to a contactor, where the bridging occurs due to carbon particles given off as the contacts open and close under load.

    So when I get a service call after say.... a storm that had blowing snow.... I know that if the unit is a Carrier, that it probably had the control section facing the prevailing wind, and snow was driven into the compartment which aided the carbon in creating the tracking between the two legs... and I will end up replacing at least two contactors in that control section as a result of the arcing, which opened up the 460 volt breaker down in the electric panel.

    Any mixture of moisture and carbon, or sufficient carbon alone, can allow for the electrons to find their way from one connector to another.

    So you can look for connector damage, but most of the time if you can't find the damage then you simply have to deduce that this is what is in play with a 460 volt or 575 volt contactor.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

    AOP Forum Rules:







  4. #17
    Join Date
    Apr 2018
    Posts
    12
    Post Likes
    Thread Starter
    Quote Originally Posted by slctech View Post
    Nice write up on that link by a guy who says he is "a know it all". Interesting how he says it is not as common indoors as it is outdoors and I never paid that much attention to when I diagnose it but I would have to agree. His pictures are not that good. I have one from a recent find that has a much more obvious carbon track.

    In the case of this system, it is 460v 3phase listed but running at around 490v respectively phase to phase. This is on a packaged chiller from the late 80's. This particular contactor is for one of the two semi-hermetic compressors. The chiller is located in a utility building on one side of the main building and the MCC box for this chiller is located in the electrical building on the other side of the main building. Found the L2 and L3 fuses in the MCC blown. I go back to the chiller and shut off and lock out that disconnect, go back to the MCC and ohm out everything to make sure it was not between the MCC and the chiller disconnect. Replace the fuses, close the MCC up and throw power back on there. Fuses held. Now back to the chiller and the disconnect, verify power on the line side of the disconnect. Open up the control cabinet of the chiller and visually inspect and immediately saw the blackened contacts of compressor A contactor. Further inspection could see the tale-tale sign of carbon tracking going from L2 to L3 or vice versa. This one was so obvious that I was able to get permission to take pictures.

    These buildings are remote so not until something happens or something is not working is when someone is called out, other than PM time. In this case I replaced the contactor and motor protector combo and double checked everything. I closed up the unit and power the unit back up. Instantly the contactor began to chatter loudly and rapidly. I shut back off the disconnect. This unit has a 120v single phase control circuit that is supplied by a transformer taking 460v to the 120v in the cabinet. The wire feeding to the liquid line solenoid had oh so slightly rubbed through against inside the MC cable sheath from nearly 40 years of vibration, it was small of a rub through that is was not enough to blow the fuse of the transformer but enough to cause a voltage drop. The contactor coil energizing and pulling in the contact was the needle that broke the camels back, it would pull in and could not hold dropping out the contactor, allowing voltage to regain and try again, dropping out again, over and over and over. This probably was going on for days for all I know but this rapid cycling of the contacts, in this case, is what quickly built up this fine specimen of carbon tracking.
    PS there was a bit of talk about contactor auxiliary switches in the PRO forum, the auxiliary seen on the contact here is to energize the remote condenser located on the roof.

    Should be three pictures of the same contactor, the close up shows a very obvious bridge of carbon that had built up and over the arc guard between the L2 and L3 Line side terminals. This little bit of carbon was what wiped out the main fuses in the MCC.
    thx a lot for sharing a picture ... it really helps understand carbon tracking. I left all the old parts at customer but i ll go back ther and observe for carbon tracking..

  5. #18
    Join Date
    Apr 2018
    Posts
    12
    Post Likes
    Thread Starter
    Quote Originally Posted by timebuilder View Post
    I can post some pictures later....but typically what I see is visible arc damage between the connectors staked on to a contactor, where the bridging occurs due to carbon particles given off as the contacts open and close under load.

    So when I get a service call after say.... a storm that had blowing snow.... I know that if the unit is a Carrier, that it probably had the control section facing the prevailing wind, and snow was driven into the compartment which aided the carbon in creating the tracking between the two legs... and I will end up replacing at least two contactors in that control section as a result of the arcing, which opened up the 460 volt breaker down in the electric panel.

    Any mixture of moisture and carbon, or sufficient carbon alone, can allow for the electrons to find their way from one connector to another.

    So you can look for connector damage, but most of the time if you can't find the damage then you simply have to deduce that this is what is in play with a 460 volt or 575 volt contactor.
    i really admire all of you guys taking such a time to help all out..
    Is there a chance of carbon tracking happening at 230v systems???

  6. #19
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    29,714
    Post Likes
    There is always some sort of carbon deposit. However, it is the voltage that makes the electrons find their way from point A to point B, and that's when the problem happens.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

    AOP Forum Rules:







  7. #20
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    29,714
    Post Likes
    Name:  Carbon Tracking terminal damage.JPG
Views: 23
Size:  180.8 KB

    Look closely at the terminals for carbon tracking arc damage.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

    AOP Forum Rules:







Page 2 of 2 FirstFirst 12

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Related Forums

Plumbing Talks | Contractor MagazineThe place where Electrical professionals meet.