Wire Size/Type Questions

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  #1  
Old 10-21-13, 12:10 PM
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Wire Size/Type Questions

I am running a circuit in non-metallic conduit underground 250' to a set of 1/2HP/220V pumps (1 HP total), and then from there another 200' feet to a second set of 1/2HP/220V pumps. All the pumps are rated at < 5 amps. I would like to include a 120V/20 amp outlet at each stop too.

My first thought is to run #1 all the way (looks like I need that for the final 120V outlet).

Can the neutral connector be smaller?

What size connector can I use for ground.

Is THHN ok for everything, or is a connector type rated for "wet" locations required? Sometime I see underground conduit that accumulates water in it. Is it assumed that all properly assembled non-metalllc conduit is watertight underground?

Thanks!!
 
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Old 10-21-13, 12:28 PM
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Last question first: Yes, you will need to use wire that is rated for a wet location as conduit installed outdoors/underground is a wet location under the NEC. THHN wire is usually multi rated wire and you will see THWN on it as well being approved for wet locations.

Now a few questions for you:
Are these 4 pump motors all separate, or are they part of an assembled "unit"?
Is the 120 volt receptacle just for convenience/maintenance or do you have an expected load?
Is there any way you could shorten the run to the 2nd set of pumps by running a separate conduit directly there?
 
  #3  
Old 10-21-13, 04:53 PM
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All pumps are separate. The first two are submersible pumps at different heights in a sump. The lower one will operate much more frequently than the upper one. Both will operate exclusively during the winter and early spring. The second set of pumps is an air compressor pump that will operate continuously, and a water pump that will operate for long periods during late summer only.

Yes, the recepticle is just for convenience. If load ever exceeds say 10 amps, use of all pumps can easily be suspended in the meantime, if necessary.

Were installiing one run of conduit to the first pumps/recepticle (i.e., we're coming out of the ground at 250'), and a second run of conduit to the final stop. We can install different size conductors in each run, if that's advisable.

Thanks in advance for any further input you can provide.
 
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Old 10-21-13, 05:29 PM
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You should not need #1 wire as the voltage drop will not be that extreme due to the low current draw. The calculations I did is for single phase, 240 volts. If your voltage is different, or the motors are three phase, let us know.

My suggestion is to run a single set of feeders for the entire run. These feeders will need to be at least #8 copper to limit voltage drop to less than 5% to all motors. By wiring them this way you will need install disconnects (with fuses) and tap off the feeder at each location. I would suggest using a #10 copper for the neutral for the 120 volt receptacles. This 120 volt circuit will also need its own fused disconnect as the main feeders over-current device will likely be rated over 20 amps, although the actual load will be less. Your ground should be #10 copper

Of course the motors will need to to have overload protection if they do not have it already.

Your feeders over-current device should be no higher than 40 amps for the #8
 

Last edited by Tolyn Ironhand; 10-21-13 at 07:06 PM.
  #5  
Old 10-22-13, 03:24 PM
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I agree that the current draw won't be that great for the 220V pumps. But don't I need at least a #1 conductor for the live (black wire) side of the 120V/20 amp outlet that is at the end of the 550' run? Then perhaps the second live (red wire) side to the pumps, and the neutral (white wire) side to the outlets, could properly utilize smaller conductors.

I'd also prefer to limit the voltage drop to less than 3%.

Thanks again, jr
 
  #6  
Old 10-22-13, 03:41 PM
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The conductor size needed to provide usable voltage at the end of a run is a function of the load attached.
I'd also prefer to limit the voltage drop to less than 3%.
From the Southwire Voltage Drop Calculator:
1 conductors per phase utilizing a #4 Copper conductor will limit the voltage drop to 2.64% or less when supplying 10.0 amps for 550 feet on a 120 volt system.
 
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Old 10-22-13, 06:29 PM
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Last time I checked, 250' + 200' = 450'

Voltage drop is determined by many factors, load being one of the important ones. (No load, no voltage drop) Your 120 volt circuit will have no load on it except when it is used, which does not sound to be very much. Also you said that the motors could be shut down if needed. I was just calculating 450' @ 20 amps for the total length. It really could be calculated 250' @ 20 amps and then take that voltage and figure 200' @ 10 amps.

Code does not require to limit voltage drop but suggest to limit it to 3% for branch circuits and 5% for feeders. Just so you know.

If you bump up the wire to #6 copper, your voltage drop would be 2.96% @ 450' @ 240 volts. If you want to spend the money on larger wire feel free. IMO it is not necessary.
 
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Old 10-23-13, 02:00 PM
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My apologies. The two runs are 250' and 300', for a total of 550'.

I appreciate that #4 or #6 copper may be sufficient for 10 amps (at 120V) at the end of the run, but I'd like to supply 20 amps at the outlet at the end of the run. Don't I need at least one (live) conductor larger than #4 or #6? Also, how much (if at all) could I downsize the neutral and ground conductors that service the two 120V outlets?

Sorry if you've already spoken to this, but I'm being too dense to see it!!
 
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Old 10-23-13, 03:11 PM
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Do you know what your 120 volt load will be? You could supply the 120 volt receptacles with 20 amps using #12 wire, but if you never load the circuit to 20 amps, what is the point? Again, voltage drop is effected by load.
 
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