480 volt transformer tripping breaker
Close
Login to Your Account
Page 1 of 2 12 LastLast
Results 1 to 20 of 37
  1. #1
    Join Date
    Jun 2007
    Location
    Vancouver Island, B.C. Canada
    Posts
    2,008
    Post Thanks / Like
    Likes (Given)
    47
    Likes (Received)
    250

    Default 480 volt transformer tripping breaker

    I have a mystery problem.
    I have 120-208 volt three phase coming into the building.
    I installed a 120/208 to 480 volt 30kva transformer to run my large roller.
    At the time I installed a 30 amp 3phase breaker to run the transformer from the 120/208 panel.

    This worked well and perfectly for a few years. Then I needed to upgrade the panel and I also needed to run my 480 volt plasma machine from the same transformer. The wires are sized correctly for the load. I have an electrician friend that does most of the work and I just help with the grunt work.

    We upsized the breaker to a 50 amp from the main panel and that is when the trouble began. The breaker trips every time I turn on the transformer. It happened the very first time and there was no load on the transformer. Reset the breaker once or twice until it will stay and then it is fine? Why is this happening?

    It is very annoying to buy a $300 breaker and have it perform this way. The 30 amp breaker did not trip. The transformer is controlled by a mag switch which uses a separate 120 volt circuit for the coil. Also the first 50 amp breaker was returned and replaced as we thought it the culprit. Seimens brand equipment.

    Any ideas from all you electron experts?

    Thanks!
    Michael

  2. #2
    Join Date
    Aug 2014
    Location
    bainbridge island
    Posts
    1,383
    Post Thanks / Like
    Likes (Given)
    300
    Likes (Received)
    343

    Default

    The new breaker is most likely tripping on the magnetic effect of the surge current, not the thermal rms Heat produced by the current.

    Try powering the transformer through 3, 50 to 80 amp slow blow fuses.

  3. Likes TDegenhart liked this post
  4. #3
    Join Date
    Oct 2017
    Country
    UNITED STATES
    State/Province
    California
    Posts
    1,276
    Post Thanks / Like
    Likes (Given)
    400
    Likes (Received)
    436

    Default

    Check the trip curve between the two breakers.

  5. Likes JST, TDegenhart liked this post
  6. #4
    Join Date
    Jun 2001
    Location
    St Louis
    Posts
    19,138
    Post Thanks / Like
    Likes (Given)
    2332
    Likes (Received)
    3555

    Default

    Depending on brand of panel, there may be a surge resistant type of breaker available. Typically that is one made for HID lighting.

  7. Likes TDegenhart liked this post
  8. #5
    Join Date
    Jun 2007
    Location
    Vancouver Island, B.C. Canada
    Posts
    2,008
    Post Thanks / Like
    Likes (Given)
    47
    Likes (Received)
    250

    Default

    Thanks for the fast replies.
    I could power this through a fused disconnect but the panel was working fine with the exact same setup with the 30 amp breaker.

    Not sure how to test the trip curve? Can you elaborate? This is a three pole breaker?

    I could try to find out if a surge resistant breaker is available but it sounds like a pile of cash and I am pretty sure they won’t take back the 50 amp I already have.

    Can anyone elaborate on why the 50 amp breaker performs poorly and the 30 was fine? There is no load on the transformer when I turn it on, so the surge is from the transformer windings? Is this just a quirk of the magnetic effect?

  9. #6
    Join Date
    Nov 2013
    Location
    Eastern Massachusetts, USA
    Posts
    6,910
    Post Thanks / Like
    Likes (Given)
    5911
    Likes (Received)
    6311

    Default

    Circuit breakers have various trip times. You need one rated for surge current due to magnetic inrush. This is common with large transformers and motors. Likely your old breaker was a bimetal type that had to heat up before tripping. The inrush current occurred over too short a time to trip it. The newer ones will trip very rapidly unless you use a model that has a built-in mechanical delay.

    The reason for the high current when first switched on even when unloaded is because the more efficient core steels often tend to act as if there is no core, only a loop of wire for several milliseconds at first application of power. The "stiffer" the source is the worse the inrush.

  10. Likes Strostkovy liked this post
  11. #7
    Join Date
    Jun 2007
    Location
    Vancouver Island, B.C. Canada
    Posts
    2,008
    Post Thanks / Like
    Likes (Given)
    47
    Likes (Received)
    250

    Default

    Scottl,
    Thanks for that clear explanation. I understood the first part but not the second.....
    Not sure why the manufacturers need to “improve” things all the time.
    Luckily it is only 20 feet to the panel but it sure is annoying.

  12. #8
    Join Date
    Oct 2017
    Country
    UNITED STATES
    State/Province
    California
    Posts
    1,276
    Post Thanks / Like
    Likes (Given)
    400
    Likes (Received)
    436

    Default

    Quote Originally Posted by M. Moore View Post
    Scottl,
    Thanks for that clear explanation. I understood the first part but not the second.....
    Not sure why the manufacturers need to “improve” things all the time.
    Luckily it is only 20 feet to the panel but it sure is annoying.
    It's likely not an "improvement" and more that you just bought the wrong breaker.

    There have always been multiple options for trip curves and I believe Siemens sells them A, B, C, or D with A being for resistive loads and D being for very hard starting loads or fire pumps or whatever. If you want a higher trip curve than that you'll need to find an old Zinsco panel.

    Check the part numbers of your new and old breakers.

  13. Likes johansen liked this post
  14. #9
    Join Date
    Mar 2009
    Location
    Eureka, CA
    Posts
    4,332
    Post Thanks / Like
    Likes (Given)
    1006
    Likes (Received)
    1722

    Default

    Not reading all the posts, I have a question...why are you switching this transformer ON and OFF. I've had a ton of equipment on transformers and they stayed ON for years, ad nauseam. Maybe your situation is different.

    Stuart

  15. #10
    Join Date
    Jun 2007
    Location
    Vancouver Island, B.C. Canada
    Posts
    2,008
    Post Thanks / Like
    Likes (Given)
    47
    Likes (Received)
    250

    Default

    Stros,
    Thank you for that info. I relied upon my electrician to buy the breaker. I believe we both thought that starting a transformer was not a big load therefore didn't need any special kind of breaker and we were using a larger breaker than had been installed prior. So this transformer should have a C or D rated breaker?

    Atom,
    I have two transformers in my shop and turn them on when needed. No need to run them all the time for just occasional use and they both buzz which annoys me when the shop is quiet. Most of my equipment runs off the 208 three phase power and I have quite a lot of equipment for a one man shop....

  16. #11
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    19,422
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    11784

    Default

    Quote Originally Posted by M. Moore View Post
    Stros,
    Thank you for that info. I relied upon my electrician to buy the breaker. I believe we both thought that starting a transformer was not a big load therefore didn't need any special kind of breaker and we were using a larger breaker than had been installed prior. So this transformer should have a C or D rated breaker?

    Atom,
    I have two transformers in my shop and turn them on when needed. No need to run them all the time for just occasional use and they both buzz which annoys me when the shop is quiet. Most of my equipment runs off the 208 three phase power and I have quite a lot of equipment for a one man shop....
    Wise to OFF them.

    That annoying buzz is just a "memo"... that you are PAYING for what causes it!



    PS: Your electrician is uncommonly ignorant. "Residential" guy, not commercial? Worse than that.

    They are neither of Physicists nor Hairy-ears.

    But they are MEANT to KNOW about the appropriate selection amongst the many and several options of breakers, fuses, load centers, and switchgear as well as conduit and wire sizings.

    Or know where TF to FIND OUT and WHEN they NEED to go seek!

    Seriously. Makers freakin' trip OVER themselves competing to make good info dead-easy to find. So they get the design-win.

    He's missed the "basics".

    Even BEFORE s**t as DOES change over time does the usual. So, too does "the Code" evolve, BTW. Meant to keep current with THAT, too. Code has added about 700 pages over my notice of it. That's only a rate of change of ten pages a YEAR. BFD.

    Whom ELSE do you expect to be in the know? The lawn-care guy? Your dentist?

    "Inspire him". To catch-up... and keep on so-doing.

    Or fire him.

    Before he gets you hurt in body, or a fire.. not just weaker in the wallet.

  17. Likes steve-l liked this post
  18. #12
    Join Date
    Mar 2012
    Location
    Geilenkirchen, Germany
    Posts
    2,819
    Post Thanks / Like
    Likes (Given)
    1600
    Likes (Received)
    1469

    Default

    All inductive loads have inrush currents. Some,depending on several factors, can be thousands of amps. These large inrush currents not only pop breakers, but are unhealthy for other equipment connected to the street distribution transformer, potentially pissing off your neighbors. These can be avoided easily by using soft start techniques. The most simple one is 3 incandescent light bulbs, one per phase in series with the input windings of the transformer. When these are in circuit, the max current will never exceed the resistive current of the bulb. Before applying any load though, you need another switch that shorts around these bulbs. That switch would then have two positions, Start and Run. Easy inexpensive solution.

  19. #13
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    19,422
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    11784

    Default

    Quote Originally Posted by steve-l View Post
    All inductive loads have inrush currents. Some,depending on several factors, can be thousands of amps. These large inrush currents not only pop breakers, but are unhealthy for other equipment connected to the street distribution transformer, potentially pissing off your neighbors. These can be avoided easily by using soft start techniques. The most simple one is 3 incandescent light bulbs, one per phase in series with the input windings of the transformer. When these are in circuit, the max current will never exceed the resistive current of the bulb. Before applying any load though, you need another switch that shorts around these bulbs. That switch would then have two positions, Start and Run. Easy inexpensive solution.
    Sheesh. Talk about bright ideas...


  20. #14
    Join Date
    Mar 2012
    Location
    Geilenkirchen, Germany
    Posts
    2,819
    Post Thanks / Like
    Likes (Given)
    1600
    Likes (Received)
    1469

    Default

    Quote Originally Posted by thermite View Post
    Sheesh. Talk about bright ideas...

    Interestingly, the inrush duration is too short to light up the bulbs.

  21. Likes JST liked this post
  22. #15
    Join Date
    Nov 2013
    Location
    Eastern Massachusetts, USA
    Posts
    6,910
    Post Thanks / Like
    Likes (Given)
    5911
    Likes (Received)
    6311

    Default

    Quote Originally Posted by steve-l View Post
    All inductive loads have inrush currents. Some,depending on several factors, can be thousands of amps. These large inrush currents not only pop breakers, but are unhealthy for other equipment connected to the street distribution transformer, potentially pissing off your neighbors. These can be avoided easily by using soft start techniques. The most simple one is 3 incandescent light bulbs, one per phase in series with the input windings of the transformer. When these are in circuit, the max current will never exceed the resistive current of the bulb. Before applying any load though, you need another switch that shorts around these bulbs. That switch would then have two positions, Start and Run. Easy inexpensive solution.
    A more "industrial" solution is to insert NTC thermistors in series with the load, with a relay that will short them out after a brief delay and also reset on power-off. This way the thermistors can cool down before the next time power is applied.

    The manufacturers make thermistors specifically intended for inrush limiting and provide guidance on selecting the appropriate parts.

  23. #16
    Join Date
    Jun 2007
    Location
    Vancouver Island, B.C. Canada
    Posts
    2,008
    Post Thanks / Like
    Likes (Given)
    47
    Likes (Received)
    250

    Default

    Two questions, if the breaker is designed to break easily and does so when switching on the transformer why does it hold if I reset? Often once will do it but usually have to reset twice.
    Second, none of the information found so far has any info on different choices of breaker, from what I can see there is only one choice in a 3 phase breaker from Siemens, however they may be available by special order but I can’t find the info. So where to find this info?

    The light bulb solution sounds good but it seems like a new breaker would be far simpler. Or a little more work to change to a fused disconnect. My wall is nearly full of disconnects but I may be able to rearrange things.
    Are there any other ways to massage the voltage?
    No complaints...I know it was three questions!

  24. #17
    Join Date
    Jul 2007
    Location
    Missoula Mt
    Posts
    1,328
    Post Thanks / Like
    Likes (Given)
    56
    Likes (Received)
    610

    Default

    Not a big deal you (not knowing anything about breakers ) bought the wrong breaker.. buy a breaker with a adj mag trip made for electric motor starting ( and transformers) will cost more $$ but will work...what not to like??...Phil

  25. #18
    Join Date
    Jun 2007
    Location
    Vancouver Island, B.C. Canada
    Posts
    2,008
    Post Thanks / Like
    Likes (Given)
    47
    Likes (Received)
    250

    Default

    Scottl was typing as I asked the question.
    There are 5000 types of NTC thermistor listed on Mouser electronics...the good news is that they appear very inexpensive if only I knew which type to buy?

  26. #19
    Join Date
    Jul 2007
    Location
    Missoula Mt
    Posts
    1,328
    Post Thanks / Like
    Likes (Given)
    56
    Likes (Received)
    610

    Default

    A NTC thermistor will nothing for you, it is the inrush amps thats kicking the breaker...Phil

  27. #20
    Join Date
    Jun 2001
    Location
    St Louis
    Posts
    19,138
    Post Thanks / Like
    Likes (Given)
    2332
    Likes (Received)
    3555

    Default

    Quote Originally Posted by Phil in Montana View Post
    A NTC thermistor will nothing for you, it is the inrush amps thats kicking the breaker...Phil

    probably won't, but only because the proper one for the current will likely not have a high enough resistance. And one that does, probably will not last.

    They perform the right action, but may not be sufficient.


Tags for this Thread

Bookmarks

Posting Permissions

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