Deciding between 120 and 480V for small pump

[mull982]

We are kicking around the idea of purchasing a small submersible pump. The mechanics are in the process of selecting a pump which will obviously have a given hp. They are asking what voltage we would like the pump to be?

We have 120V, 208V, and 240V and 480V avaliable. Is there a cutoff hp rating for determining what voltage to run to a particular motor or load. I have heard that 2hp was the cutoff or maximum for using 120V? What are some other common cutoffs for various hp's and voltages, as well as deciding between single phase and three phase?

 

[charlie b]

Regarding single phase versus three phase, I would draw the line at 1/2 HP. Anything larger gets a three phase motor. Regardless of the motor HP, if it is a hree phase motor and if I have 480 volt three phase available, I ask the mechanics to specify that voltage, rather than 208. I prefer not to use 208V three phase unless using 480V would require some dramatic design choice, such as installing a 480 volt panel on a penthouse level to serve only one 480V load.

 

[Besoeker]

We are kicking around the idea of purchasing a small submersible pump. The mechanics are in the process of selecting a pump which will obviously have a given hp. They are asking what voltage we would like the pump to be?

We have 120V, 208V, and 240V and 480V avaliable. Is there a cutoff hp rating for determining what voltage to run to a particular motor or load. I have heard that 2hp was the cutoff or maximum for using 120V? What are some other common cutoffs for various hp's and voltages, as well as deciding between single phase and three phase?

I'm from UK.
The voltage choices are generally much simpler.
For LV, we have just 230V single-phase and 400V 3-phase.
Maximum loading from one single-phase outlet is around 3 kW.
Dedicated circuits may be greater. I have seen directly heated showers rated at 9 kW.

Apologies for the digression.
For a motor over a few hundred Watts I'd go 3-phase.

 

[BryanMD]

Given so many choices I'd be inclined to go with the one that relates to the rest of the system or machine the pump supplies... same panel, same conduit, etc.

 

[petersonra]

I am inclined toward a 3 phase motor above a certain size say 1/2 or 3/4 HP.

I don't like oddball voltages so would stick with 240/480. Most decent 3 phase motors are dual voltage anyway.

Having said that, other factors might come into play. Like the pump already comes with a 230V single phase motor, and I have 230V available.

 

[mull982]

Regarding single phase versus three phase, I would draw the line at 1/2 HP. Anything larger gets a three phase motor. Regardless of the motor HP, if it is a hree phase motor and if I have 480 volt three phase available, I ask the mechanics to specify that voltage, rather than 208. I prefer not to use 208V three phase unless using 480V would require some dramatic design choice, such as installing a 480 volt panel on a penthouse level to serve only one 480V load.

Any particular reason why you use 1/2 hp as the cutoff between single phase and three phase? 1/2 hp is equal to about 373 watts. Any particular reasons why you use this number?

 

[charlie b]

Any particular reason why you use 1/2 hp as the cutoff between single phase and three phase? 1/2 hp is equal to about 373 watts.

Not really. A previous company for which I worked drew the line at 1HP. My current company draws it at 1/2 HP. Three phase motors are smaller and run more efficiently. So I don't have a problem with the smaller cutoff line.

 

[mikeames]

Too many variables here.

How big is small?

How far is the run?

Are all voltages available from the same location?

I would choose my voltage/pump based on the above questions.

 

[weressl]

Not really. A previous company for which I worked drew the line at 1HP. My current company draws it at 1/2 HP. Three phase motors are smaller and run more efficiently. So I don't have a problem with the smaller cutoff line.

This is especially true for submersible pumps that are a special construction.

 

[Jraef]

Here's a thought. Any change you MIGHT go with variable speed any time in the future? If so, go for 230V 3 phase for the motor. The VFD will be less expensive.

 

[mull982]

Thanks for the feedback guys. Like I said we were tossing around the idea of purchasing a small submersible pump and someone asked what voltage we should get. Someone made the comment that anything above 2hp should be a 480V motor. I'm guessing that this is because 2hp is aprox 1500W which equates to 12.5A at 120V. Since most breakers (fed from a panel) are 15A then this 12.5 was the max.

After hearing this I began to wonder more what standards there were to back up this statement. I also began to wonder not only above the voltage requirement but the phase requirement as mentioned. It seems like the generall consensis is that anything above 1/2 hp should be a 3phase motor regardless of voltage. Main reason being efficiency?

It turns out that the pump we are going to order is a 1/2hp pump. We are going to go ahead and utilize 120V which is avaliable. This pump will have a float swich imbedded in the pump to turn the pump on and off.

My question is how motor protection is done for such small pumps. Is there overload protection imbedded in the pump to protect the motor. If not, in the case of feeding this pump from a panel, do the panel breakers have to adhere to table 430.52?