Proper wire size?

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Old 04-29-08, 04:20 PM
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Question Proper wire size?

We are having a new well drilled and changing from a 110v jet pump to a 1/2hp220v submersible pump, from the main panel running off a 2 pole 20amp breaker going to the new pump control box where the waterline enters the cellar is 75feet. The well guy said quote "I can get by using #12 wire" does this sound correct? or should I use #10 wire?
 
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Old 04-29-08, 04:33 PM
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you did not give the well depth. the wire must run down the well to the pump.

with the 75 feet, you shouldn;t have any problem with #12 but there is no rule against using #10 if you want.

that pump should only be a few amps so your voltage drop will be minimal for quite a long distance.
 
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Old 04-30-08, 12:29 AM
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You should have total length from the house breakerpanel or pressure switch to the well head and from wellhead to the pump itself that is the total length and senice you mention half hp motor on 240 volts that not drawing much current and 75 feet will not really affect the voltage drop at all

{ 1/2 hp motor @ 240v 1 typically draw about 4-41/2 amp range }

Merci,Marc
 
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Old 05-01-08, 02:58 PM
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total distance

The pump will sit about 240ft down the well its another 40ft to the house and 75ft from pump contol to the main panel which is the part I'm responsible for they do the rest, my estimate says they'll run 12/4 out of the well and to the house and you are correct 1/2 hp pump at 220v draws 4.5a..Long story short total distance is approx 355ft..
 
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Old 05-01-08, 03:30 PM
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That is a pretty deep well; I have to agree that #12 wire borderline in this case. My calculation shows a 2.8% voltage drop with 5A load at this distance. Code recommends that voltage drop be limited to 3%, however motors are more sensitive to voltage drop especially during start-up.

However even if you replace the 110' from the panel to the wellhead with #10, you only improve the voltage drop to 2.5%. Doing the whole run from the panel to the bottom of the well in #10 give you a 1.8% drop.

Are you sure they're installing 12/4 pump cord and not 12/3 cord?
 
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Old 05-01-08, 05:16 PM
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given that depth, I would go with the #10 for the reasons Ben posted.
 
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Old 05-01-08, 05:27 PM
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I just ran the caluatator and you are about right on the borderline with #12 wire unless the pump itself is rated on 208-240 they can take a bit of swing of voltage.

really i rather run with #10 anyway due many time i did see submersbaile well pump often upsized to 3/4 hp or so so that will cover that part.

Merci,Marc
 
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