Wire Size

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Clipper9

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Location
Rochelle IL.
I have a sprinkler pump I am running wire to. And I was wanting to get some input about the size I was thinking of using. The pump pulls 10 amps at full load, It's about 500 ft run so I was thinking of using a #10 wire. Do you think that could handle the drop?
 
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gndrod

Senior Member
Location
Ca and Wa
Clipper9 said:
I have a sprinkler pump I am running wire to. And I was wanting to get some input about the size I was thinking of using. The pump pulls 10 amps at full load, It's about 500 ft run so I was thinking of using a #10 wire. Do you think that could handle the drop?
Click to expand...

Is that a 1hp pump at 240vac? Ten AWG would work.
 
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eHunter

Senior Member
Location
North Texas & Georgia
Clipper9 said:
I have a sprinkler pump I am running wire to. And I was wanting to get some input about the size I was thinking of using. The pump pulls 10 amps at full load, It's about 500 ft run so I was thinking of using a #10 wire. Do you think that could handle the drop?
Click to expand...

A #10 may work but there will be close to 6% VD on the circuit.
Here is a URL for a handy tool:

http://electrician2.com/calculators/motor_ver_2.html
 
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gndrod

Senior Member
Location
Ca and Wa
petersonra said:
The OP says 10 Amps.

500 feet is a long way. thats a lot of wire.
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I agree, especially for my humorous 24vdc pump at 10amps. I used a Flint & Walling pump motor chart for a 1 hp, 230v, 1 ph, at 630 ft as an example of what would work using 10 AWG. (Just to be on the safe side.)
 
beanland

beanland

Senior Member
Location
Vancouver, WA
1-phase vs. 3-phase

1-phase vs. 3-phase

Let us not forget that the voltage drop for a 3-phase motor is 1/2 that of a 1-phase motor because of the return path loss. So, the correct answer is "all of the above." Clipper9 needs to provide voltage and phasing. (1-phase vs 3-phase, 120V? 240V? 208V? 480V?)

Then, too is the allowable voltage at the motor. If a 240V motor is rated to function per manufacturer specs down to 208V then the voltage drop can more than 3-5% and the motor will run fine.
 
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Clipper9

Member
Location
Rochelle IL.
more info.

more info.

I guess I should have given more info. sorry. It's a single phase 1.5 HP motor at 240 volt supply the data plate says 9.8 FLA.. It will only run for a 10 to 15 min. at a time
 
kwired

kwired

Electron manager
Location
NE Nebraska
Clipper9 said:
I guess I should have given more info. sorry. It's a single phase 1.5 HP motor at 240 volt supply the data plate says 9.8 FLA.. It will only run for a 10 to 15 min. at a time
Click to expand...
Is this a deep well pump, or a shallow well or booster type pump? 1.5 HP seems like a lot for most applications unless it is a deep well or you are moving a pretty large amount of water. I am assuming we are talking about lawn watering sprinklers or similar.
 
beanland

beanland

Senior Member
Location
Vancouver, WA
Backwards Process

Backwards Process

Here is how I would consider it: Allow 3% voltage drop. On 240V that is 7.2V. Current is 10A. Allowable impedance is 7.2V/10A = 0.72 ohms. Wire distance is 1000ft. Allowable resistance (impedance) of wire 0.72 ohm/kft. #8 copper is 0.76, #6 copper is 0.50. Use #6 copper to stay below 3%. You can probably live with #8 copper; voltage drop is 7.6V or 3.2%. (please note that I cheated by using resistance rather than impedance but in small wires in a conduit, that is a good approximation.)
 
kbsparky

kbsparky

Senior Member
Location
Delmarva, USA
What if the motor is rated for 208-230 Volts? Would you still be concerned with such a drop, when the resulting supply voltage is within the range stated on the nameplate of the motor?
 
beanland

beanland

Senior Member
Location
Vancouver, WA
208V Delivery

208V Delivery

Is the motor is rated for use down to 208V and if the service voltage was 5% below normal, say 228V rather than 240V, then the total allowable voltage drop is 20V @ 10A for 2 ohms. In that case, #12 copper would be acceptable from a voltage drop standpoint. With a continuous load of 10A, minimum ampacity is 12.5A so #12 is acceptable.

However, if the motor starting current is 6x, the voltage drop would be 120V during starting, there is a good chance that the motor will not have sufficient torque and will fail to start. Since this is a pump load, it may be possible to spin this up to speed but it may trip the breaker on the thermal overcurrent element.
 
kwired

kwired

Electron manager
Location
NE Nebraska
beanland said:
Is the motor is rated for use down to 208V and if the service voltage was 5% below normal, say 228V rather than 240V, then the total allowable voltage drop is 20V @ 10A for 2 ohms. In that case, #12 copper would be acceptable from a voltage drop standpoint. With a continuous load of 10A, minimum ampacity is 12.5A so #12 is acceptable.

However, if the motor starting current is 6x, the voltage drop would be 120V during starting, there is a good chance that the motor will not have sufficient torque and will fail to start. Since this is a pump load, it may be possible to spin this up to speed but it may trip the breaker on the thermal overcurrent element.
Click to expand...

As voltage drops so does starting current. Which is some of the principle behind how and why soft starters work.
 
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