3 phase 230v 30 hp pump motor

I'm trying to properly size a three phase service to provide power for a 30 hp submersible pump. I'm going to run 4/0 copper ( 200 amp ) for a commercial three phase service. The problem I'm having is figuring the breaker size for the pump itself. The paper work says that the full load is 80 amps. The service factor maximum load is 91 amps. There are two circuit breaker columns. One for (maximum per NEC) - 225 amps. One for (typical submersible) - 200 amps. An inspector I talked to said these were maximums but that he would use a 150 amp breaker with #2 copper leads. His multiplying factors just didn't ring true to me but I haven't done motor work in 20+ years. I always thought that you multiply full load by 125%. He said it could be as much as 175%. Obviously he chose 150%, right in the middle. Well then, what determines which you use ? I'm more than foggy on this. I think he was too. Any input ? Please, only professional input here. Thanks in advance.

 

Based on the 91 amps, the feeder to the motor is based on the full load plus 40% (430.22(E)=127.4

Your feeder conductors need to be sized to handle that load-#1 copper or 2/0 AL.

OCPD, if inverse time breaker is used 250%, if time delay fuse is used-175%, and if non time delay fuse is used-300%.

 

Wirenut 1110,

Thanks for the input. Very much appreciated !!!

So since I'm using a standard molded circuit breaker/ D ( QO ) series, that would be another term for an inverse time breaker, correct ?

I then need to multiply 127.4 x 250% = 318.5 OCPD ???

What about the table for the motor that lists 225 amp and 200 amp OCPD respectively ?

 

I'll add, if the motor is considered continuous duty, then it's only 125%. Which I doubt it is.

 

The 250% is based on the FLA of the motor(this is an up to size) to allow for motor starting.

91X2.5=227.5 or 250 amp breaker.

What table are you speaking of?

 

Personally, I would tap the service entrance conductors and put a fused disconnect for the mammoth

 

wirenut1110,

I think this qualifies as a continuous duty motor. It's for irrigation well pump.
The table is the one from the pump motor company. It's a general pump info page for various voltages and HP s.

The pump has a electronic control box that allows for variable speed ramp up. No hard starts.

I don't really have to tap the SEs. This service is going to be new and solely for this pump. so I can pretty much arrange this set up how I want. Other thoughts ?
I want to keep it neat and as compact as possible. It's going to be in a field. In the open.

 

wirenut1110,

The 225 OCPD was on their chart as max allowable according to NEC. So at 227.5 amps, You're right on. They show (typical for submersibles) on that chart at 200 amps. I guess I just stick with what they wrote.

That's a big breaker for a 30 hp, No ? Geeze.

 

Then yes, you and the AHJ needs to follow the manufactures instructions. This pretty much trumps all in the NEC.

If it's continuous duty, then the conductors need to be sized at 125% of the motor FLA.

Edit: yes, I stated that the code says that's the MAX but the manufacturer, from testing and so on, has determined that the 225 is the max and 200 is usually ok too.

Yes it is a big breaker

 

wirenut1110,

Thanks so much for your time and input. I really appreciate it.

 

wirenut1110,

One last thing,

If I end up using a 225 breaker for this as the max, Is it required that I install a 300 amp service instead of the 200 amp I planned ??? I wouldn't think so since it's for start up purposes only. But not sure. I am going to install 2- 120v circuits for lights and service outlet in the cabinet.

 

You do not need to use 4/0 copper for a 200 amp service. 4/0 aluminum, yes. Copper, no.

The info I get here: electrician2.com Motor Circuit calculator says you need the following (using the worst case scenario)

Voltage: 200-240
HP: 30
Phase: 3
Type of motor: Not design B
Class of service: Continuous
Duty Cycle: Continuous
Nameplate Current: 80A
Conductor Material: copper
Temperature: 78-86F
Number of CCC in raceway 1-3
Service factor is 1.15 or greater: Yes
Temp rise is not over 40C: Yes
Conductor insulation: THWN 75C
Termination temp: 60C

Results:
Conductor size: #2 copper
Equipment Grounding Conductor: #8
Non time delay fuse: 250A
Time delay fuse: 150A
Instantaneous trip circuit breaker: 700A
Inverse time (standard) trip circuit breaker: 200A
Overload protection: 100A

 

Tolyn ironhand,

Thanks. I would use 3/0 copper as needed one up size for commercial application but no supply carries it. That's why I upped to 4/0. The owner spec'd copper. Thanks for the motor calculator link !!!

 

Tolynironhand,

I got a feeder size of 3/0.

 

You stated "The pump has a electronic control box that allows for variable speed ramp up. No hard starts."

With the information provided by the pump supplier your 200 amp service should be fine. If the "electronic control" you mention is a frequency drive, you will see no large inrush but will need to get pump to 1/2 speed in 2 seconds to provide bearings with proper lubrication. Submersible pumps don't start moving water until about 1/2 speed. If the "electronic control" is a Soft-Start your inrush will be reduced based on you starting ramp. That ramp should be a step where you get to 1/2 speed then ramp up slower to full speed. If you are using a frequency drive you need to follow the manufactures wire sizes from the drive to the motor as conductor size and length could be a concern depending on distance from drive to pump. I never heard of a wholesale house that did not stock 3/0 copper for a 200 amp commercial service, they should be able to get it for you.

 

You may want to do some research on your service because I think you will have difficulty finding a 200 amp branch breaker for a 200 amp service.

I'm not 100 % sure if some make a 200 amp 3 phase feed through main breaker panel, I know they do it in single phase. From what I've seen, 125 is the max branch breaker.

If you'll have other loads where the controller is installed, maybe install a 200 amp fusible disconnect, feed the controller/drive from there and tap off of the load side and install like a 100 amp load center for lights/receptacles, etc.

Just a thought.

 

3/0 copper THHN/THWN is a very common wire size used for commercial/industrial 200 amp services and feeders. I would be highly surprised if a real supply house wouldn't stock it. The big box stores typically carry 2/0 copper for residential 200 amp services.

Ths is the quick motor data calculator I like by Scheider Electric.

Three Phase Motor Data

This calculator says you need #3 wire, 100 amp time delay fuse or a 110 amp thermal breaker. The easiest way to do this is to install a 200 amp service with a 200 amp service entrance rated fusible switch (NEMA3R if it is outside, NEMA1 if inside), fused at 100 amps with time delay fuses. The next most cost effective way to do it is to use a service entrance rated MLO panelboard with about 12 spaces and a 110 amp breaker. The supply house will figure out the catalog numbers and pricing of the panelboard and a bolt-in breaker to fit it.

This is all based upon actual voltage being 240 volt and not 230.

 

when sizing wire for a VFD, input wiring is based completely on the size of the VFD not the motor, the wire from the motor to the VFD should be the same size.

If the VFD has a Bypass contractor, then wire must be sized for inrush.