120 or 240 Load Balancing

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  #1  
Old 06-19-02, 03:21 AM
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120 or 240 Load Balancing

Dumb Question #653

Getting ready to wire my well pump at 120 or 240VAC.

Have the right size wire and length for either voltage.

Is there such a thing as load balancing?

If the pump runs at 120VAC do I use more meter watts than wiring it at 240VAC? Or theoretically, if outlets, lights and pump were wired on just one 120VAC leg and there were no other 240VAC items (stove, dryer, water heater), should the electric bill be the same as if they were staggered evenly between both 120VAC legs?

Any other advantages to wiring the pump at 240VAC rather than 120VAC?

Thanks
 
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Old 06-19-02, 06:35 AM
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Yes, there's such a thing as load balancing. This only applies if you decide to use it at 120 volts. Balance the load on the two legs of the power. 240-volt loads are self-balancing. Balancing is for safety, and should not affect your bill.

Your electric bill should be essentially the same whether you run it on 120 volts or 240 volts. There is slightly less loss in the wire at 240 volts, but unless the run is long it won't make much difference.
 
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Old 06-19-02, 09:44 AM
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There is a definite advantage in operating the pump motor on 220 volts. The resistance of the circuit conductors to the motor is a "fixed" value we'll call R. The full-load motor current is I. The motor current for 220 volt operation is 1/2 the value of 120 volt operation . If I is the motor current for 220 volt operation then 2I is the motor current for 120 volts.The power loss in the conductors= I X I X R. If I =2 for 220 volt operation the PL = 2 X 2 X R = 4R. For 120 volt operation PL= 4 X 4 X R = 16R, 4 times the PL for 220 volt operation.
 
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Old 06-19-02, 10:13 AM
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The voltage drop issue is correct. Although if you actually calculate the power loss effect on your bill, it is relatively small. Sometimes I make the choice based on how many circuit breaker positions are available in the panel. If there a lot of space, then go with the 240V model (if all things are equal regarding equipment cost and availablity).
John is correct, that if you chose a 120V model, place the circuit breaker on the lowest electrically-used phase in your panel for equal balance/safety.
 
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Old 06-19-02, 11:00 AM
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The I X I X R power loss in the circuit conductors is not a concern in terms of economy but for effective circuit performance. If the starting surge on the motor is 300% of the running-current then on starting the circuit power loss for I=4(running-current) is 12 X 12 X R = 144R. This could be a problem because of the lenth and the size of the motor-conductors.
 
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Old 06-19-02, 10:58 PM
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There seems to be a major discussion about voltage drop and advising 220 volt when we don't even know the distance of the branch circuit involved.

Using a rule of thumb and voltage drop calculations, if you are running a branch circuit of proper sized conductor and your branch circuit is not longer than 125' then 120 volts would be fine and installing a 220 volt pump would not save you money. If you are installing a branch circuit longer than 125' but not longer than 250' then you should install a 220 volt pump due to the distances involved. The voltage drop of a 120 volt circuit is within normal design factors if not running more than 125". A voltage drop of a 220 volt circuit is within normal range up to 250' If you are running more than 250' with proper wire size per minimum ampacity ratings then you may need to either boost the voltage above 220 volts or increase the size of conductors to compensate for any voltage drop involve.

HOpe this helps

Wg
 
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Old 06-20-02, 06:37 AM
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Wg, I like those rules of thumb and had not previously heard them. It's a good way of getting a ballpark feel without doing the math.

So hopro, how far away from the panel is the pump?
 
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Old 06-20-02, 06:03 PM
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For a 20 amp circuit with a maximum load of 16 amps this is what the calculator provides as an answer, with a 3% limitation to voltage drop:
Length (ft) Minimum Conductor

20 12
60 10
100 8
150 6
 
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Old 06-20-02, 08:16 PM
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Ron, I don't think those numbers are correct (20 feet for #12 seems way to short!!!). Any chance you ran the calculation for aluminum wire? Did you run that calculation assuming 120 volts or 240 volts -- the answers would be different.

Here's what my voltage drop calculator says, for 16 amps at 240 volts (divide the distances by two for 120 volts). All distances are shown one way (i.e., half of the voltage drop occurs on the outbound and half on the inbound).
  • 12-gauge copper will lose 1% of the voltage (i.e., 2.4 volts) every 45 feet. Thus you could go 135 feet before you lose 3%.
  • 10-gauge wire loses 1% of the voltage every 71 feet. Thus you could go 213 feet before losing 3%.
Doing a bit of reverse engineering, Wg's rule of thumbs seem to be allowing for about a 5% voltage drop, and are assuming the standard size wire for the breaker, and about 75% loading. That's in the ballpark, which is all you can expect from a rule of thumb.
 
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Old 06-21-02, 05:00 AM
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In using a voltage drop calculator program, 120V, 16A, PF=1, copper, 60 ft, #12 awg results in 3.84 volt-drop or 3.2%.
Here's a link (not to the one I used originally, but similar results)
http://www.elec-toolbox.com/calculators/calculators.htm
 
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Old 06-21-02, 06:04 PM
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The NEC now suggests by FPN Note 5% voltage drop on a branch circuit or a feeder or a combined voltage drop of 5%.

If you held to the 5% voltage drop you should be able to travel a distance with a 125 volt branch circuit the following distances at 16 amps.

16 amps @ 125 volts and 12 awg = 98 feet = 4.97% voltage drop
16 amps @ 125 volts and 10 awg =157 feet = 4.98% voltage drop
16 amps @ 125 volts and 8 awg =251 feet = 5.00% voltage drop
16 amps @ 125 volts and 6 awg =398 feet = 5.00% voltage drop

Some of hte calculators on the net are either inaccurate in their programing or the operator is missing something in their info.

I like to use a calculator that asks you the questions and you can see it work as you answer the question. Then I feel a bit more safe. Problem is with a lot of hte calculators like demand load calculators the people don't know what they forgot to enter becuase all you see is a small box. You can't see do its work.

Be careful using auto calculators unless you know it is accurate.

just an opinion

Wg
 
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