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  1. #1
    Doug W is offline Hot Rolled
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    Default Motor trips breaker? Why?

    I have a 1 1/2 hp single phase baldor motor on a Burr King grinder.
    wired 115v draws 13.5amps.
    The circuit is 20 amp with about 12 ft #12 romex from breaker to plug. 25ft extension cord also #12. Nothing else on the circuit.

    Sometimes on startup it will start, get up to speed, run for about 15 seconds and trip the breaker.
    Sometimes it will be running for a few minutes unloaded and trip.
    I have never had it trip while grinding.

    No smoke, no smell of anything shorting.
    All connection look good and tight.
    Any ideas?

  2. #2
    gar
    gar is offline Stainless
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    Default

    Put an ammeter in series and measure the current vs time. Maybe also put voltmeter across the motor leads at the motor. During startup you may draw 70 or more amperes for maybe 5 seconds or more. That warms the breaker quite a bit.

    Are you using a Sq-D QO breaker?

    .

  3. #3
    macplus is offline Cast Iron
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    Default

    Do you have anything else that is powered from the same breaker?

  4. #4
    JunkyardJ's Avatar
    JunkyardJ is offline Titanium
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    Unhappy I've had bad breakers do stuff like that.

    I put a clamp on meter on there where the hot wire goes into the breaker. It registered 12.2 max amps (wasn't fast enough to pick up the starting current) running my little pancake compressor. It would blow the breaker right before it filled up all the way. The compressor ssaid 13.8 amps on it, so there wasn't anything wrong with it. Replaced the breaker, and it never blew again (without something actually being wrong). So, check the current, first. If the current is OK, replace the breaker. Sometimes they're just a little too touchy and blow before they're supposed to. I also had a breaker that would blow because the screw was loose where the wire went in causing it to get hot. Check that out too, the wire will be hot going into the breaker.

  5. #5
    DaveKamp is offline Titanium
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    Thumbs down HOMline?

    I had very similar things happen... but with much less loading. I made the mistake of installing a Square-D HOMline breaker panel in my garage-shop at previous residence, and this building wasn't formally 'heated'. Had five light sockets (with 60W bulbs, so 350W, or about 3A) in there on one switch, and if it was cold in there (under 30F), and I flipped that switch on, the 20A lighting breaker would pop.

    Of course, every other similar breaker would nuisance-trip whenever temp was below 30F, so I had a feeling that it was a 'factory' problem.

    I checked the physical connection (as noted above, a poor conx at the breaker will cause connection heat (from resistance) to percolate into the element, and cause a nuisance-trip). didn't fix it. Tried a new HOMLine breaker, didn't solve it.

    Ended up ripping out all the HOM's and substituting something else (Think it was Siemens, I-T-E, GE or similar) and all the trip-problems went away.

    Of course, when it's above 60F, the breakers would work just fine.

    I sent a message to Square D about it, and they blamed it on about 9 different things, but denied ever having seen or heard of this issue before. After talking with a few professional electricians, they all came back with the same response- that HOMs were junk...

    ...so the only Square-D thing we use now is QO.

  6. #6
    JST's Avatar
    JST
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    Incidentally, the QO is available in a high inrush type breaker. Actually I think there is more than one. If you look on their site there is a manual of the Q0 stuff.

    In any case, one type is for mercury/sodium lights.

    The dual breakers are NOT what you want. We had some at the old work, and turning on a 10A variac would pop them about 30% of the time.

  7. #7
    Doug W is offline Hot Rolled
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    Replying to the questions.

    1. Only the grinder is on the circuit.
    2. Breaker is Square-D HOMline, that seems to be suspect.
    3. I don't have a clamp on meter, perhaps I will borrow or buy one.

    Probally will just try better breaker, and see if that stops it.

  8. #8
    peterh5322's Avatar
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    "Breaker is Square-D HOMline, that seems to be suspect"

    Definitely suspect.

    Designed for "built to a price point" residences.

    Definitely not Q0 quality or performance.

    Frankly, I don't know why Square D brought out the Homline line.

    Probably a business decision from Schneider (France), Square D's new "masters".

  9. #9
    Doug W is offline Hot Rolled
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    OK , I went to buy a better breaker and the A0 series looks like it would not interchange with the HOMline breakers.

    So Where or how do I get a better breaker to install in a HOMline panel?

    Thanks

  10. #10
    gar
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    You don't. You want a QO panel.

    Get a small QO panel. Feed that from a larger breaker in the HOMline box with appropriate size wire for that larger breaker. Make sure to follow the rules for your safety ground wiring. Put the 20 A QO breaker in the smaller panel and from the 20 A breaker feed your #12 wires to the motor. Make sure any QO breakers you buy are not counterfeit.

    The other option is to reconnect your motor for 240 V and use a 2 pole HOMline 20 A breaker and the same #12 wires for the same wiring resistance. This reduces your current to 1/2 and the startup percentage voltage drop to 1/4 (absolute startup voltage changes to only 1/2, but when taken as a percentage of the source voltage it is 1/4) .

    .

  11. #11
    2Slow's Avatar
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    I'd just buy a new Homeline breaker and see if that solves your problem. before I went to the trouble and expense of upgrading to QO.

    That said, I run QO in my houses and shop.

    -Joe

  12. #12
    JST's Avatar
    JST
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    The homeline do not offer the options and variety that Q0 do.......

    Most of the Homeline seem to be about like the cheapest of the Q0, only a step below. So you get a typical "builder's quality" (that means cheap) box, with fast acting thermal breakers which cannot tolerate a heavier current or inrush.

    They get hot, they trip at a lower current. They WILL warm up with a near-capacity load on them.

    Long term load on a 20A breaker is only allowed to be 16A. You have 13.5........

    A few things...... How's the voltage drop with that extension?

    If the voltage drops too much, the current can go up rather quickly. Then the motor may not ever get high enough in speed to open the start winding.

    Or, the motor may just sometimes fail to disconnect the start switch, and so there is way too much current, and the breaker is correctly opening. Switches CAn get sticky, weld shut, then later break loose and seem OK.

    Seems you are OK, since your current is within decent limits...... so presumably the breaker is just doing it's "cheap thing".

  13. #13
    Pierce Butler is offline Hot Rolled
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    Quote Originally Posted by JST View Post

    Long term load on a 20A breaker is only allowed to be 16A. You have 13.5........
    JST,


    I have looked for that spec and cannot find it. Where is that spec at??? I have needed a source of data like that for a while now and never could find it.

    thanks!!!

  14. #14
    gar
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    Pierce Butler:

    Go to your library and the a NEC code book.

    Using Google with the following search string:
    nec continuous load on 20 amp breaker

    Produced these two and many more results, but not a direct answer to your question.

    http://www.wsdot.wa.gov/NR/rdonlyres...ing1082004.pdf

    http://forums.mikeholt.com/showthread.php?t=61450

    The reason is that if a breaker is rated at X amperes, then it may trip open with a continuous X ampere load. You want some margin. The general criteria is 80% of breaker rating, or the breaker should be 125% (the reciprocal of 80%) of the continuous load.

    A criteria like this is only common sense, but common sense does not define the criteria value. The value comes from field experience, controlled experiments, and judgements.

    .

  15. #15
    Doug W is offline Hot Rolled
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    An update.
    I now don't believe it is the breaker.

    I removed the motor, brought it to the elecrical panel so I used only 6ft of #12 wire.
    Tried 3 different HOMline breakers all with the same "popping" results.

    I now have noticed when it is going to trip the breaker, the motor vibrates substantally and makes a growling noise from the point I plug it in till it trips. 25% of the time.

    Conversely if at plug in there is none of that it will start and run fine. 75% of the time.

    Start circuit not disengaging?

    I also repeatedly tested the breakers with a unmounted 3hp 20amp motor. Sluggy startup but never tripped.
    Last edited by Doug W; 02-08-2008 at 12:27 PM. Reason: more info

  16. #16
    macplus is offline Cast Iron
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    Since it is a single phase motor you could have a problem in the starting circuit of the motor, start capacitor, start switch, governor switch, start winding or a combination of any of them.

    I have a 1 1/2 hp single phase baldor motor on a Burr King grinder.
    wired 115v draws 13.5amps.
    The circuit is 20 amp with about 12 ft #12 romex from breaker to plug. 25ft extension cord also #12. Nothing else on the circuit.

    Sometimes on startup it will start, get up to speed, run for about 15 seconds and trip the breaker.
    Sometimes it will be running for a few minutes unloaded and trip.
    I have never had it trip while grinding.

    No smoke, no smell of anything shorting.
    All connection look good and tight.
    Any ideas?


    If it's a capacitor start / capacitor run type motor, the problem could be the run capacitor has open circuit.
    If the motor is good, the last thing I would check is the incoming feed to the panel and make sure everything is nice a tight.

  17. #17
    Forrest Addy is offline Diamond
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    I suggest you get a "motor rated" breaker. Residential breakers plain don't have the cohones for motor starting. After X starts they nuisance trip. Then you have to replace it. And again. I have a Square D QO panel and never had a bit of trouble. But then I don't have many larger single phase motors to start.

  18. #18
    JunkyardJ's Avatar
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    Unhappy It's probably SHOT.

    Either it's a bad cap, there's something major wrong with the motor like the bearings. If it's got a run capacitor, replace it. If it doesn't have a run cap, the motor is probably shot. It MIGHT be the bearings, when they start to fail, it can cause a motor to suck a LOT of excess juice. That's usually what a "groaning" noise is with intermittent problems. If it's easy to rebuild, it might be worth it.

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