tripping breaker at start up
- Thread starter mannyb
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Yes, you use the table for sizing the breaker and the conductors.
Assuming 480V supply, 150A may not be too small if you are looking an an MCP breaker or anything with adjustable mag trips. The mag trips can be adjusted up to 800% of FLA, more under special circumstances.
If the breaker doesn’t have adjustable mag trips, it’s too small.
Assuming 480V supply, 150A may not be too small if you are looking an an MCP breaker or anything with adjustable mag trips. The mag trips can be adjusted up to 800% of FLA, more under special circumstances.
If the breaker doesn’t have adjustable mag trips, it’s too small.
You use table 430.247 for amps for conductors? and Table 430.52 for OCP ? Also if the breaker isnt MCP the breaker would be sized 124a x 250% =310A for breaker ?
Thanks for all your help.
The MCP for motor are set a MAX for 150a breaker. Is there anything the NEC allows to be done in a case like this? The pump pulls water from a reserve tank that sits 400' away. The breaker trips when they havent run in a long period of time I suspect the water pipe has emptied and trips because its pulling water while empty cause breaker to trip. The breaker settings are at it max setting. Either than the pump is to small for pressure needed.
ptonsparky
Tom
- Occupation
- EC - retired
Can you take a picture of the MCP so we can see the settings?
How long does it run before tripping? Does it pump open discharge or against some kind of resistance? Have you actually measured the current?
ptonsparky
Tom
- Occupation
- EC - retired
. (Aimed at the OP, not you)
This thread started as if this were a very new installation. It appears to me, that may not be the case. Why were you called in? Has this system ever worked? If so, what changed?
The current of a pump motor lifting 400’ of water may be significantly different than that of one moving it from point a-b at the same level.
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- Placerville, CA, USA
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- Retired PV System Designer
Which suggests that some sort of flow restriction (possibly a pressure independent orifice rather than a simple valve) could prevent a low grade overload (thermal trip) when starting up empty.
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- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
It's important to know if the breaker trips IMMEDIATELY, as in under 1 second, or trips after a few seconds. The mag trip setting issue would be involved only in the under 1 second scenario. Anything after that and it is a thermal trip issue. Different concerns.
Sorry for late response. Yes the breaker trips immediately at start up. It doesnt do it all the time but enough to be a problem, nothing on starter trips or settings only the breaker.
Yes SIr the pump draws water from a reservoir tank that sends the water to another tank. I cant remember that part of system but I will check tomorrow it that could be an issue with blockage at discharge.
ptonsparky
Tom
- Occupation
- EC - retired
Open discharge will cause the current for a centrifugal pump to go up. That is when it will be moving the most water and doing the most work. A restriction will cause less flow, less work, and less current. There have been many threads here that have touched on this
Make sure someone has not opened a valve that should be partially closed.
i see now that you posted the MCP trips immeadiatly, while you need the information above for future reference it is no longer relevant for your situation.
You need test equipment. Does the motor pass the smell test at its J-box or peckerhead?
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ptonsparky
Tom
- Occupation
- EC - retired
Did this motor ever start and operate as it should or has this been an intermittent problem from the start?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Max setting on a 150A MCP will be 1500A. Motor nameplate FLA is 112A (I am assuming 460V, because 230V would have never worked at all with a 150A MCP...). If the motor is an "energy efficient" design, the NEC would allow the breaker to be set for up to 1300% of 112A, so 1456A. But if it's proven to be a problem AND it is indeed an energy efficient Design B motor, you can go to 1700%, or 1904A, an acknowledgement that this is a known issue with EE motor designs. But your breaker will not go that high. You would need a new MCP breaker, 250A frame. If it's a combo starter, it may not fit. This by the way has nothing to do with the pipe being empty or full if it happens immediately. Water doesn't flow immediately anyway, this is an issue with the motor magnetizing current. Can we assume the motor has been meggered and is fine? If so, this is probably a known issue with the type of motor being used.
Alternatives are to use a Soft Starter instead of Across-the-Line, which comes with other benefits for pumps. 100HP is above where I usually start thinking about using a soft starter anyway.
Or faced with no other option, I've also had success changing the breaker from an MCP to a Thermal-Mag version of the same frame size. In my experience the T-M breakers don't trip as easily on the same inrush spikes, I think because the thermal trip elements add a small amount of dampening, often just enough to avoid nuisance trips like that. Just make sure it has adjustable mag trips too, and set them to max again
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- Wisconsin
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- PE (Retired) - Power Systems
But typically T-M breakers only go as high as 10x for their magnetic setting. I have been using electronic trip instead of TM because they can often go to 15X the sensor. Of course they need to be physically interchangeable.
Yes The motor is everthing you just mentioned. I did find some new information because it finally stop raining The feeder ocp 150a breaker set at highest setting 8. Both are Siemens FXD6 Lo to HI setting The motor starter has MCP a set at 6.The MCP doesnt trip but the 150a OCP for feeder trips once at start up. after that its fine. I would have thought the MCP would trip first.Thanks for all your help
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Sorry for late replies. I have been working late and dont have time to reply to question for this post.I did find out a couple things when i went back for more information. The motor feeder is protected by a 150a breaker. The feeder goes to motor starter that also has a 150a breaker Siemens fxd6. The breaker at panel trips first and the one at starter does trip at all. The breaker trips at first initial start but works fine after that. The MCP at pump is set at 7 trip setting and the feeder breaker with same breaker trips at #8 setting. I was wondering if the the breakers had to be synchronized or adjsted so the feeder breaker does trip first. Thanks for replies
ptonsparky
Tom
- Occupation
- EC - retired
MO: You have a horserace going on. The Feeder bucket is winning. The motor is either too big or your motor circuit from start to finish is too small. Somebodies screwed up from the get go.
Jraef and others have explained what can be done.
Having one vs the other trip first just saves steps for the guy that has to restart things.
Yes I understand. I just not sure if I was sharing all the information to make an informed decision.
If I can beat this one more time. The siemens fxd63a150 series breaker has Trip settings to 1500. The fxd63H150 has trip settings to 2500. I know I can use max but this would allow me to set a higher trip setting. Is that something to consider also. BTW I appreciate all responses.
If I can beat this one more time. The siemens fxd63a150 series breaker has Trip settings to 1500. The fxd63H150 has trip settings to 2500. I know I can use max but this would allow me to set a higher trip setting. Is that something to consider also. BTW I appreciate all responses.
ptonsparky
Tom
- Occupation
- EC - retired
Maybe someone else has figured out which different model # breaker you have where, but I haven’t. If you can turn up the one that is tripping, turn it up.
You really need outside help to do any more.
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