Sizing Breaker for 250HP pump

[Jimmy4645]

Wondering if you guys can help me out? Working on a well pump station project that has a 250 HP pump (310 FLA) being installed. The service to the building is 600 Amp @ 480V,3Ph. The pump has an Allen Bradly Magnetic Starter. I'm not sure what size breaker I should utilize?

Thanks

 

[Jraef]

Where are you going to put the breaker? I.e., is it going to be a feeder in a panelboard feeding a non-combination starter, or is it going to be in the same control panel with the starter? Or is the A-B starter already a combination starter and all you are doing is feeding it from a service?

 

[Jimmy4645]

from a motor control center. It will be a combination motor starter

 

[Cow]

Across the line on a 250HP well pump? Yikes. The biggest motor I've seen across the line is a 350HP for a pellet mill...

It makes a guy wonder how long the payoff would be to use a soft start or VFD instead of racking up peak demand charges from across the line starts? We've done 200HP across the line for booster pumps but all the larger wells we've done have been VFD's with pressure transducers.

 

[dbuckley]

Across the line on a 250HP well pump? Yikes. The biggest motor I've seen across the line is a 350HP for a pellet mill...

There's a recent thread with a 8,000HP motor being started direct on line.

Yeah, i nearly fell off my chair

 

[augie47]

any idea what your load is now without the motor ??.
You may be on the edge of trouble with a 600 amp main and a 250 ACL motor.

jraef historically provides excellent motor advice.. be patient....

 

[lt2000]

any idea what your load is now without the motor ??.
You may be on the edge of trouble with a 600 amp main and a 250 ACL motor.

jraef historically provides excellent motor advice.. be patient....

+1 on jraef's advice.

 

[BAHTAH]

Well Pump

Well Pump

Wondering if you guys can help me out? Working on a well pump station project that has a 250 HP pump (310 FLA) being installed. The service to the building is 600 Amp @ 480V,3Ph. The pump has an Allen Bradly Magnetic Starter. I'm not sure what size breaker I should utilize?

Thanks

Don't turn on the electric heater while starting the pump. Ha Ha. I would look at a VFD. Is this the only pump, or is there a booster pump in addition to the well pump? On all the wells I have done, if the well is left as non-operational for any period of time, you have to pump water to waste to clear any impurities before the well can be closed into the water system. We always pump to waste at a much lower rate using a VFD and then pump into the system using pressure or flow to control the speed of the well pump. In addition if there is a clay-valve that takes time to close the VFD allows you to pump to waste at a lower rate until the valve is closed. I could be making many wrong assumptions here since you did not say what kind of well you are working on, just my two cents worth.

 

[Jraef]

from a motor control center. It will be a combination motor starter

I guess I'm being thick here, I still don't quite get it.

So are you wanting to size a FEEDER breaker to go into an MCC that will feed a remote combination starter? If so, size the cables to feed the load and account for the voltage drop, then size the FCB to protect the cables. The motor short circuit protection will be taken care of in the remote combo starter.

Or are you going to try to build your own combination starter to mount into an MCC? If so, why not buy a starter from the manufacturer that will fit in there? You can't UL list your own version anyway, but maybe that's not important to you, I don't know.

If it's not important, then size the breaker per article 430 of the NEC for motor loads. I don't have my NEC on this laptop or I'd give you an example.

 

[augie47]

Jraef, with more input, can give you a far more knowledgable answer, but until then....... If you are installing a combination starter, the breaker they used can give you a clue, but, my concern with no other data, wiuld be that Art 430 for the motor shortcircuit/ground fault protection per 430.52 would allow
a 800 amp breaker..(430.52) .larger than you present main.
As far as what is need, if you provide the LockedRotor Code (430.7), knowledgable folks like j might provide more assistance.
Some engineerihg asssitance might prove well worth it's cost in this case.

 

[Jimmy4645]

I was told that the starter will be a FVNR Size 6 NEMA starter installed in the MCC and that the Circuit Protector is 600A and that i should run a 500~600 amp feeder..??

 

[Cow]

Your feeder is sized to the motor ampacity tables in 430.250 if it's 480 volt. Multiply by 125% for a continuous load and that's the minimum size conductor required for your motor. For motor loads, it's not required to size the feeder to the breaker size. Take a look at Table 430.52, I believe.

 

[kingpb]

You better look at the main 600A breaker protection curve. Assuming it has an adjustable instantaneous setting, you will need to make sure that it is set high enough to not interfere with the motor inrush on start-up, but also look at the fault current because if you set it too high, it may not trip quick enough for a fault.

I plotted a 400A (mtr protection) and a 600A main breaker and looks like you can coordinate it, assuming all the stars align properly.

Another issue though could be the transformer feeding the MCC, if it is the utility, it could very well be undersized anyway. Depending on the size, it may not allow enough system impedance through it to allow the motor to start at all, or in a time frame that keeps it within it thermal damage.

Is this going to cycle on and off frequently, or is it run full out all the time.

May be a good application for AFD (variable flow) or soft starter (full flow).