Single Phase Pump vs Three Phase Pump

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Three phase will have more economical operating costs over time. With pumps, this is extremely important. A pumps operating costs over time far outweigh the initial capital investment of the pump.

3 phase, with the highest voltage available will draw the fewest Amps, Amps are what you pay for ALL the time, if you reduce the amp draw, you reduce the overall cost of the pump over the lifetime of the pump.

No... you pay for power... power is watts. So... 1000 watts is still 1000 watts whether single phase or 3 phase.

True that "watts is watts", but if the three phase motor is more efficient than a single phase motor delivering the same power output, you'll use less watts.

Agreed... using less watts is always a good thing.

But... if two motors, one single phase and the other 3 phase, had the exact same ratings (efficiency, power factor etc.) and were both 5hp, the cost to operate is identical for both motors.

So what about us guys who like to run our three phase motors on single phase just to go against the grain?

wattwät/nounnoun: watt; plural noun: watts; symbol: W The SI unit of power, equivalent to one joule per second, corresponding to the power in an electric circuit in which the potential difference is one volt and the current one ampere.
Of course we pay for power, but the FLA on a 5hp motor on 3 phase with 460 volts is 7.6 amps.
And the same motor on single phase with 120 volts will draw 56 amps FLA.
So which would you rather pay for on a pump that may run 24/7 for a municipal water tower?

If you discount the efficiencies of the motors and the nature of the power delivery system... there ARE NO savings in using a three phase source over a single phase source. Horsepower is horsepower whether from a single phase or 3 phase source.

The difference is in how that power is delivered.

Don't believe me... do the math.

Hello North:

You're not considering the extra cost of a start winding, centrifugal sw. and start capacitors, all of them subject to failure, and in my experience, much sooner than the run windings.

The 3 PH motor is the simplest of the motors, and as I said before, creates its own starting torque, no need for anything that will be of no use while running, exept in the case of start-run capacitors, but that is just one type of single phase starting method.

Agreed... I am only considering the energy consumed by the motors themselves. My comments on this are based on the comment, from Massey, that a 3 phase motor consumes less energy (if everything else is equal) than a single phase motor of the same size. Period...

Remember,

This question is from the same guy who brought us:

Operating at 230V

Circuit Breaker

Phase Rotation and other questions of an elementary nature.

It seems clear that all this discussion is being squandered on someone who does not understand electrical theory or codes.

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I'm surprised you were rated off topic, specially regarding the first paragraph of your post, I agree with you, and I would only add that a 3PH pump doesn't require an extra starting device to create a rotating magnetic field and starting torque; the rotating magnetic field is inherent to the 3 phases' 120 electrical degree shift.

No capacitors to dry out.

No charred or worn centrifugal sw. contacts

No starting problems whatsoever, as long as the motor is properly rated and not burn't.

Here's a GA for you pal !

Thanks Yahlasit.

Make sure you are connected or have access to a (3) phase grid

It depends on the application and whether there are power demand and/or minimum power usage stipulations from the power supplier.

For applications 5HP and under there are minimal to no savings realized by using 3 phase equipment.

If the pump is a stand-alone application that will not be operating more than 50% of the time the standby and demand power charges can easily offset any possible savings realized and in most cases over a long period of time will cause the cost of 3 phase power service to far exceed the cost of using single phase power.

As far as the cost of rewinding and maintaining a 3 phase or single phase motor is concerned there is little to no difference on motors rated at 5HP and less.

I don't understand all of that. Can you elaborate?

What are standby power charges? I believe peak demand power charges are based on max power in any 30-minute period, so as JRaef said in #10 starting peaks are unlikely to affect it. How do these charges differ for 1 and 3 phase?

I assume OP has both systems available, clearly the figures might be different if he was deciding which system to install.

You cannot ASSume that 3 phase motors are more efficient, some single phase motors have equal or even better efficiency than equivalent 3 phase versions. The only thing that matters in that regard is the rated efficiency as stated by the motor mfr, if you believe it (bottom feeders are known to cheat).

So as others have said, you do NOT pay for amps, you pay for watts, and watts are watts regardless of phases. As to demand charges, most utilities use a sliding demand window anyway, so a brief peak of starting current has almost no effect the overall demand charges. Only in the most extreme cases do utilities charge for what is called "instantaneous" deman. Yet because a rare few do, the suppliers of mitigating technologies pounce upon this to over exaggerate the benefits of their technologies in mitigating it. There may be other perfectly legitimate reasons to soft start motors, but contrary to popular belief, demand charge mitigation is almost never one of them.

We will just have to couple a single and three phase motor face to face and see who wins.

Dear Mr. cckla,

Single Phase Motor means higher current for the same power and hence wire/conductor size will be bigger than the 3 phase, Voltage drop will be Higher, Starting Current will be further high. Starting device - like capacitor connected - fault means you cannot start the motor since the single phase motor cannot start on its own. since the Torque is REVERSED INSTANTLY DEPENDING UPON THE FREQUENCY. As mentioned motor is costlier.

Three phase means, especially Star connected (where the Line Current = Phase Current), conductor/cable size required will be smaller, Voltage drop is Smaller, Starting current will be relatively lesser than Singl Phase Current. TORQUE REVERSAL DOES NOT OCCUR.

DHAYANANDHAN.S

If you have 3-phase supply available I see next to no reason not to use it, for reasons given in #14 by Yahlasit, and others.

If three-phase power is not available, the great advantage of a single-phase pump is that it will work on a single phase supply.

Single phase will work on a 3 phase also, just drop a leg

But 3-phase won't work on a 1-phase supply . Not unless he installs an inverter, which might not be a bad idea.

correct'o mundo