Well pump wiring dilemma

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  #1  
Old 09-23-11, 12:17 AM
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Well pump wiring dilemma

Here is the problem I have a 1/2 horse submersible well pump that is about 150 feet from the house. The people who had the house before ran direct burial wire 10/2 to well pump. Once at the well head the wire enters the control box where it is connected with the 14 gauge pump wire going down to the pump. This wire was protected by double pole 30 amp breaker at the house. Since I've moved I have built a well house over well and trenched in conduit and new water lines. I also put in a 50 amp sub panel for other things like outlet and lights. My question is should i continue to use a 30 amp breaker or downsize to say 15 amp double pole breaker. The pump is 230volts rated at 6.2 amps. Would there be any problems having the pump protected with a 30 amp breaker and having 10/2 connect to 14 gauge pump wire. My other thoughts were if I installed a 30amp disconnect with 10 amp fuses would that protect the pump if the breaker never trips.
 
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Old 09-23-11, 04:50 AM
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Welcome to the forums! I would use a 15 amp disconnect and leave the overall 30 amp protection at the house. 30 amps is too high a circuit protection for that pump. You will find, however, you won't be able to use the 10-2 to the pump house and incorporate lighting. You have no neutral. So along with the conduit, did you run new wires for supply to include a neutral? You didn't say in your post.
 
  #3  
Old 09-23-11, 06:02 AM
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You can only have one circuit as a feeder to an outbuilding.

The breaker for the pump needs to be sized to allow the motor to start up. Often times the startup current is several times the run current.
 
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Old 09-23-11, 06:19 AM
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Also, the breaker basically has nothing to do with what's on the other end (your pump). It's primary purpose is to protect the wiring to help prevent an overload and fire. So even though 30 amp may be too large for your pump it is proper for protecting #10 buried wire.

Hopefully someone else can chime in about code but I don't think dropping to #14 wire to go down the hole is allowed. Code would require you to drop down to a 15 amp breaker to protect the smaller #14 wire. I think the wire down the well should also be #10. Staying with #10 wire is also a good practice to minimize the voltage drop over the length of wire going down the well.
 
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Old 09-23-11, 07:18 AM
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I see the dropping to number 14 for the well wire the same as using #18 zip cord on a lamp or use of #12 in a stove wired to a 50a breaker but not a pro.

I also put in a 50 amp sub panel for other things like outlet and lights. My question is should i continue to use a 30 amp breaker or downsize to say 15 amp double pole breaker.
The original line needs to be abandoned and everything including the pump should be off the 50a subpanel because as PCboss wrote:
You can only have one circuit as a feeder to an outbuilding
The well wire is not a continuous load and is not building wire which is what the charts refer too. Another factor is the max thermal limit of the insulation on the wire not just the size of the copper. Again not a pro though and do mit know what wire is to the pump.
 

Last edited by ray2047; 09-23-11 at 07:38 AM.
  #6  
Old 09-23-11, 10:50 AM
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The pump should have a 15A breaker. When sizing the breaker for a motor circuit you ignore the usual rules and instead look at the amps of the motor. Code allows a maximum breaker size of 250% the amps of the motor, in this case 6.2 * 2.5 = 15.5A.

In practice you should use the smallest breaker that will reliably allow the motor to start which is usually 1.5-2.0 times the motor current, however in this case that is a moot point because 15A is already the smallest available breaker.

As far as I know there is no problem dropping #14 into the well as long as the pump draws less than 15A, which it clearly does in this case. Even if this was a very deep well you would not see significant voltage drop with a 1/2HP pump.
 
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Old 09-24-11, 07:16 PM
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Yes I ran 4 wires in the conduit to a 50 amp sub panel in the well house. Right now the panel has a quad breaker with 30 amp double pole and 2 20 amps for other circuits. I think I will just use that breaker somewhere else and put in the 15 amp dole pole for the well pump. My well in only 80 feet deep. I just didn't know if there was a negative to using a 30 amp vs the 15 amp double pole. Next question would be should I swap out the wire I have running to the control box and pressure switch from the subpanel. From my well sub panel I have #10 wire to switch and control box. With a 15 double pole do I need to run 14 gauge instead of 10. If I ran the 14 gauge it would be the same gauge as the wire going down the well to pump. Also at the disconnect if the pump draws 6.2 amps and I have 2 fuses what amperage should they be ideally.
 
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Old 09-24-11, 07:58 PM
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Next question would be should I swap out the wire I have running to the control box and pressure switch from the subpanel. From my well sub panel I have #10 wire to switch and control box. With a 15 double pole do I need to run 14 gauge instead of 10.
No, the #10 is fine, just heavier than it needs to be. If it's in place and the pump is running, I'd just leave it as is.
 
  #9  
Old 09-25-11, 06:25 PM
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Disconnect fuses

ok thanks for all the help guys but I have one more question about the disconnect fuses. If I run the 15 amp double pole breaker for my well pump and the pump is 1/2 horse 6.2 amps should the fuses be 15 amp also. If there is 2 slots in the disconnect do the fuses add up to the amperage needed or is the amperage needed the same for both slots. Example if I need 10 amp fuse does that mean 10 amp for both slots or 5 amp in each slot. My disconnect has the push in type fuses vs screw in
 
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Old 09-25-11, 06:33 PM
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Both fuses need to be the same rating, they are not additive. With a pump they really should be "time lag" fuses and of the smallest rating that allows the pump to start under the worst case. If the circuit breaker is now in the same space as the disconnect you really don't even need the disconnect. Ten ampere time lag fuses should be fine.
 
  #11  
Old 09-25-11, 06:34 PM
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Originally Posted by marlinbrando View Post
ok thanks for all the help guys but I have one more question about the disconnect fuses. If I run the 15 amp double pole breaker for my well pump and the pump is 1/2 horse 6.2 amps should the fuses be 15 amp also. If there is 2 slots in the disconnect do the fuses add up to the amperage needed or is the amperage needed the same for both slots. Example if I need 10 amp fuse does that mean 10 amp for both slots or 5 amp in each slot. My disconnect has the push in type fuses vs screw in
Fuses and a disconnect aren't even required if you are coming off the breaker in your subpanel. I think you should use at least 15 amp fuses, 20 or 30 amps might assure they never blow. The protection will be the 15 amp breaker. Or, if you want to be more precise on the protection, follow Furd's advice and use 10 amp time delay fuses.
 
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