Page 20 of 21 FirstFirst ... 1018192021 LastLast
Results 191 to 200 of 209

Thread: Why do they both trip???

  1. #191
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,577
    Quote Originally Posted by jim dungar View Post
    Yes page 6-47 includes the code for the part number.
    Did you look at page 6-91?
    The letter T, in position #8, indicates the breaker has Long time (e.g. thermal) tripping. There would be a letter I here, if this was a Motor Circuit Protector frame for magnetic only protection.
    pg 6-47 also shows a note for the T code as LSI an industry std term for LongShortInstant



  2. #192
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,577
    Quote Originally Posted by 310 BLAZE IT View Post
    I if we're being 100% technically correct let's call it a transient.
    and transients can be incident/refracted/reflected
    we are assuming it is coming from the loads, could be on the supply, and since set so low is tripping first, then the 2 branch breakers

    a wave hitting a xfmr is reflected almost 100% so the source sees twice the magnitude of the incident wave in the load reflected wave

    imo they are all set too low



  3. #193
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    9,675
    Quote Originally Posted by Ingenieur View Post
    pg 6-47 also shows a note for the T code as LSI an industry std term for LongShortInstant
    Just like I noted in post #185.

    It appears that you heard hoof steps and thought of Zebras instead of horses.
    I think it is time to stop digging. and look back to what the OP has posted throughout this thread.
    Just because you can, doesn't mean you should.

  4. #194
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    30,360
    Quote Originally Posted by gadfly56 View Post
    All true, but no one calls the main fire pump or booster fire pump service a "fire alarm booster panel", "FA supply", or "fire alarm control panel". Not to mention they wouldn't be coming out of a distribution panel in any event.
    Actually the pressure maintenance pump can be supplied from the normal service or the fire pump service, but I otherwise agree you almost never hear it called a "fire alarm" anything, maybe a "fire pump" something though.

  5. #195
    Join Date
    Jan 2016
    Location
    PA
    Posts
    2,577
    Quote Originally Posted by jim dungar View Post
    Just like I noted in post #185.

    It appears that you heard hoof steps and thought of Zebras instead of horses.

    I think it is time to stop digging. and look back to what the OP has posted throughout this thread.
    you didn't even hear the hoof steps apparently
    why is what you think more important than what I think?

    if the info presented is accurate there is no solution so the client must live with it:
    no abnormal switching transients can be identified
    no faults on the system
    the breakers are set correctly and can't be set higher for some reason

    I would selectively set breakers higher to identified which branch was the source (main, 70 or 100)
    or just set all higher to 800-1000% and call it a day
    300% is way too low

    the 70 has perhaps 8 A (feeds a 45 kva transformer loaded to ~ 6 kva)
    the 100 has 25 A (feeds a subpanel that feeds a small 7.5 kva xfmr loaded to 1 kva)

    imo the problem is on the supply side (and interaction with the xfmrs)
    but in reality the problem is the 300% setting
    illogical
    Last edited by Ingenieur; 03-21-17 at 09:25 AM.



  6. #196
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    30,360
    Quote Originally Posted by Ingenieur View Post
    300% is way too low


    For pretty much any inductive load that is placed "across the line" when energized. Sure it may hold sometimes, or even quite a bit of the time but that is low enough you can't expect it to hold every time.

  7. #197
    Join Date
    Feb 2003
    Location
    Massachusetts
    Posts
    59,850
    Quote Originally Posted by Ingenieur View Post
    the breakers are set correctly and can't be set higher for some reason
    That is a strawman, no one has said that at all.



    I would selectively set breakers higher to identified which branch was the source (main, 70 or 100)
    or just set all higher to 800-1000% and call it a day
    300% is way too low
    So you are good without finding the reason they are tripping and simply cranking up settings.

    Duly noted.

  8. #198
    Join Date
    Jun 2003
    Location
    NE (9.1 miles @5.07 Degrees from Winged Horses)
    Posts
    8,248
    Quote Originally Posted by iwire View Post



    So you are good without finding the reason they are tripping and simply cranking up settings.

    Duly noted.
    Sounds like a plan from this side of the river.
    Tom
    TBLO

  9. #199
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    30,360
    If you replaced them with a breaker that didn't have magnetic trip adjustment, chances are the fixed magnetic trip is at least 600 or even 800% of the breaker rating.

    I really don't know you can turn them too high from a overcurrent protection perspective, any specific setting you do put them at is for selective coordination purposes - with the intent that the branch breakers will trip before the main does if there is a fault on a branch circuit.

    If you turned the main up, I'd bet your random tripping event ends up only tripping the branch breakers.

    If you turned up the branch units but not the main, you probably only see the main trip during whatever event is occurring.

    How much to turn each one up is for selective coordination, they are still going to protect the wiring from short circuits and ground faults even at maximum settings.

  10. #200
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    30,360
    Quote Originally Posted by kwired View Post
    If you replaced them with a breaker that didn't have magnetic trip adjustment, chances are the fixed magnetic trip is at least 600 or even 800% of the breaker rating.

    I really don't know you can turn them too high from a overcurrent protection perspective, any specific setting you do put them at is for selective coordination purposes - with the intent that the branch breakers will trip before the main does if there is a fault on a branch circuit.

    If you turned the main up, I'd bet your random tripping event ends up only tripping the branch breakers.

    If you turned up the branch units but not the main, you probably only see the main trip during whatever event is occurring.

    How much to turn each one up is for selective coordination, they are still going to protect the wiring from short circuits and ground faults even at maximum settings.
    Let me say this assumes what is there already is in compliance with the available fault current and AIC ratings as well as any series ratings for downstream devices.

Posting Permissions

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