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#98929 - 06/26/06 01:13 PM well ckt  
watersparkfalls  Offline
Member
Joined: Mar 2005
Posts: 222
Washington...Not DC
I have a customer that needs a well wired up. the well head is 410 feet from the house and a 30 amp circuit. using the normal volt drop formula to stay within 3-5% for the motor i would use #2AL use and run a direct burial ground with it.
after talking to the well company they said i can use normal 10-3 uf to feed the pump motor in fact the spec sheet they faxed me says i could go 1020 feet. why is this? is the volt drop not a factor because the motor is in water vitually liguid cooled?
i was curious to other ideas or if anyone else has run across this scenerio too.

thanks,
H20


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#98930 - 06/26/06 01:45 PM Re: well ckt  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,141
Estero,Fl,usa
What is FLA on the motor. The 30a might indicate 175% of FLA is greater than 20 thinking along the lines of 240.4(D) instead of 430 rules.

They could also simply be wrong.


Greg Fretwell

#98931 - 06/26/06 01:59 PM Re: well ckt  
markp  Offline
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Joined: Apr 2004
Posts: 60
Kent, WA, USA
You said a "30 amp circuit", but what is the nameplate amps of the pump motor? A 2 HP pump would be a huge well pump, and would have a nameplate value of about 12 amps. Code permits motor breakers to be upsized quite a bit, so its hard to know what amps to calculate when all you see is the breaker size. I would expect your pump to be 1 HP or less (about 8 amps at 240V).

I would be surprised to see a 30A breaker on a motor that had a nameplate value of 10A or less, and I'd also be surprised to see 10-2 allowed for 1020 feet on a motor with a nameplate amp value over 8 amps or so.


Mark
Kent, WA

#98932 - 06/28/06 12:06 AM Re: well ckt  
watersparkfalls  Offline
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Joined: Mar 2005
Posts: 222
Washington...Not DC
the motor is a 1/2 HP, not sure actual nameplate since its in the well case already. so 430-148 fla is 4.9, is that the number to plug into the Volt Drop formula for the "I"?

VD=2*K*I*L/CSA
VD=2*12.9*4.9*410/10,380
VD=51,832.2/10,380
VD=4.99

i thought "I" was always the breaker size it was connected to.?


#98933 - 06/28/06 10:22 AM Re: well ckt  
markp  Offline
Member
Joined: Apr 2004
Posts: 60
Kent, WA, USA
If you want to use the breaker amp rating for "I" you can, and that would give you an extremely conservative circuit that will have acceptable voltage drop even during starting. But I think this is overkill, and its going to cost way more than what I think you really need.

I don't believe there are any code rules with respect to voltage drop, just some guidelines. I would use the nameplate * 1.25 in the voltage drop calculation and try to keep it under 3% (7.2V).

I think that 30A breaker requirement must be wrong. Perhaps if it was wired as a 120V motor, but that still seems too large. For a 5 amp 240V motor, I would think a 15A breaker would be just fine.


Mark
Kent, WA

#98934 - 06/28/06 12:15 PM Re: well ckt  
gfretwell  Offline


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Joined: Jul 2004
Posts: 9,141
Estero,Fl,usa
My V/D calculator comes up with the same thing so I think you will be OK on #10 and I agree on the 15a breaker. I have a 1/2hp well pump that is doing fine on a 15.
Them pushing this out to 1020' may be a stretch but it still only works out to about 5% V/D (12v from 240). I am guessing that is where the number came from.


Greg Fretwell


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