Questions re: Electric Load Form (new electric service)

[Zebu Fellenz]

Hey Everyone,

I'm beginning the process of having electric service run to a property that currently has no utility connections.

The electric is needed for an irrigation well project that's happening later this year. The first step it to fill out and send in the electric load form that describes the expected usage and service configuration requested. I'm having issues figuring out what the total connected load KVA & KW along with the expected peak demand should be (also KVA & KW).

Part of the issue is not knowing yet exactly what size motor will be in the well and the second and larger issue is not having any clue how to figure the load in KVA?

My expectation is that the well will either be a 7.5hp or 10hp motor (depending on depth and water available) and will almost certainly be a 3 phase motor running on single phase service through a VFD drive.

Assuming 7.5hp the motor will be a M75432 Goulds and the VFD will be a SPD20150F Goulds drive. If it ends up being a 10hp motor the drive will be upsized to a SPD20200F.

Going by the specs from Goulds it looks like required input current (230v single phase) is 64.3a for the smaller drive and 81.7a for the larger.

This well is going to be the only large electrical demand on this service. The only other loads will be a couple of 20a 115v utility circuits.

Thanks in advance for any input.

-Cheers,

Erik

 

[Bert_]

Good rule of thumb is 1kva per hp.

I think I would double check those currents listed. They seem very high. Generally on single phase a 7.5 hp motor is ~35A, 10hp ~45A. Can't see why a pump motor would be much different.

Seems like a standard 200A service, which is often served by a 25kva transformer, would work great and leave room for more load.

 

[Zebu Fellenz]

Good rule of thumb is 1kva per hp.

I think I would double check those currents listed. They seem very high. Generally on single phase a 7.5 hp motor is ~35A, 10hp ~45A. Can't see why a pump motor would be much different.

Seems like a standard 200A service, which is often served by a 25kva transformer, would work great and leave room for more load.

Here are the specs for the 7.5hp pump motor:

Brand Goulds Pumps
Model Number M75432
Type 3 Phase Submersible Pump Motor
HP 7.5
Phase 3
Volts 230
Amps 26.4
Full Load Amps 24
Locked Rotor Amps 140
Full Load Watts 7480
Service Factor Watts 8570
Line - Line Resistance 0.55-0.85
SF 1.15

I know the VFD drive needs to be upsized when using single phase input, maybe that explains the input current appearing high?

 

[Bert_]

Here are the specs for the 7.5hp pump motor:

Brand Goulds Pumps
Model Number M75432
Type 3 Phase Submersible Pump Motor
HP 7.5
Phase 3
Volts 230
Amps 26.4
Full Load Amps 24
Locked Rotor Amps 140
Full Load Watts 7480
Service Factor Watts 8570
Line - Line Resistance 0.55-0.85
SF 1.15

I know the VFD drive needs to be upsized when using single phase input, maybe that explains the input current appearing high?

Single phase current can be calculated by multiplying 3 phase current by 1.73.

2x hp rating is common when running a drive on single phase input. Doesn't mean it draws 2x current.

 

[Zebu Fellenz]

Hey Bert,

Thanks for the help so far! I think my numbers might be messed up because the install books for the VFD assume three phase input and there's not a separate chart reflecting single phase input.

Running on three phase input the full load output current of the SPD20150F is 47.4a, nominal HP is 15, fuse size is 70a, and generator size is 20500VA.

Next is noted that on single phase input maximum output of the drive and horsepower of motor must be derated to 50% current.

On single phase input the full load output current is 26.4 (slightly more than 50%). Does this mean that all other specs are cut by the same percentage?

-Thanks Again,

Erik

 

[Bert_]

Your pump is 24A. 24x1.73=42A on 1 phase.

 

[sberry]

sometimes its not about the actual load but the number of connected pieces. I put one in where they wanted 3K to install for a well,,, when I said I want to put in a second and a cooler there were 1000$ credits. I said,, well ****, I am building all kinds of stuff on they passes on the connection fee. List a well, an air comp and a cooler.

 

[sberry]

Another not too long ago wanted 3500 maybe more for a drop but if there was a building permit for a new house cost 150 the cost was wayyyyyyyyyyyyyyyyyyyy less and mostly the underground fee of 3 bucks a foot.

 

[wyliesdiesels]

Is 3phase service available? IF so i would go with that then just use the VFD for variable flow rate/PSI....

 

[Zebu Fellenz]

Is 3phase service available? IF so i would go with that then just use the VFD for variable flow rate/PSI....

Three phase might be available. Concerns (if it is available) are the likely higher install/hookup cost and differences in the billing methods/rates.

If I was planning for higher electric usage and consistent 12 month demand three phase would be a no brainer (if available).

 

[Bert_]

Is 3phase service available? IF so i would go with that then just use the VFD for variable flow rate/PSI....

I would check into it but even if the lines run right by I'd consider the costs.

If this will be the only 3 phase load a VFD and single phase input might still be a good option. The base fee just to have 3 phase will be quite a bit higher. Install cost will be more as well.

A 7.5 or 10hp motor and VFD is no big deal on a single phase service. It would be different if it was a bunch of motors.

 

[Jim greengo]

Good rule of thumb is 1kva per hp.

I think I would double check those currents listed. They seem very high. Generally on single phase a 7.5 hp motor is ~35A, 10hp ~45A. Can't see why a pump motor would be much different.

Seems like a standard 200A service, which is often served by a 25kva transformer, would work great and leave room for more load.

What he said.

 

[sberry]

My 400 is fed 15.