pump wire sizes

You may remember I asked about the pressure switch wire for my pump last week...
The group convinced me to replace all the wires and put in conduit. More
investigation shows I should move the pump control box to near the pressure switch at the same time, in the basement.
Anyway, I now will have a 380 foot run from the basement to the well with 2" conduit installed. The pump uses three wires with loads as follows: red wire - 27.5 amps, black wire - 19.1 amps, yellow wire 10.8 amps. I learned I need THWN wire last week. What wire sizes should I order?
Karl
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I don't have my book at home to figure it out but, explain to me why the imbalance, I'm curious.

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The run cap sits at the top of the well in the control box, the motor is at the bottom of the well. These are leads that you normally don't see when you have a motor with L1/L2 and included cap. The yellow and black amps add to the the red amps with a bit of phase shift to account for the difference.
Tom Gardner wrote:

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wrote:

If you have a long run and high current, mighy be a good time to consider a relay close to the pump, you can run thinner wires from the switch to the relay... Joel in FLorida ========> investigation shows I should move the pump control box to near the pressure

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Well, I didn't read the original post carefully enough, I guess the relay was a stupid suggestion, considering the long run is from the source to the pump - not much you can do here except use larger wires - if the switch is a long way from the pump, a relay would let you use lighter wires to and from the switch... joel


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Your load could be (maginally) handled by a #10 wire in terms of not overheating the wire and insulation. So that means you need to size the wire for voltage drop. A quick calc (assuming 2 wire circuit) says that #10 copper will give you slightly over 10% voltage drop out at the well head, #8 gives 6% drop, #6 would give you 4% drop. If this is an extreme service unit (running for weeks on end during the summer when the grid supply voltage is sagging), go with the heavier wire.
Karl Townsend wrote:

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...
I assume you're talking the red wire. How does a #6 red, #8 black, and #10 yellow compute? I need to order Monday morning.
This is just a V=IR problem. Anybody know where to find R per 100' on different wire sizes?
Karl
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On Sun, 13 Jul 2008 11:53:42 -0500, with neither quill nor qualm,

Would that be for A/C, D/C, or Bisexual wire, Karl? <wink>
http://www.epanorama.net/documents/wiring/wire_resistance.html http://www.eskimo.com/~billb/tesla/wire1.txt http://www.wiringfordcc.com/trakwire.htm
P.S: Shouldn't guys with pumps be asking about _pipe_ sizes instead of wire sizes? ;)
--
"Giving every man a vote has no more made men wise and free
than Christianity has made them good." --H. L. Mencken
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Karl,
    guage:        ohms/foot:     8        .000628     6        .000395     4        .000248
Hul

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Roy J sez:
"I don't have my book at home to figure it out but, explain to me why the imbalance, I'm curious"
If I might take a stab at it, my W.A.G. is:
Karl, like so many who build RPCs, probably lost sight of the need to properly balance the idler-motor / load network. They throw in a few random-valued capacitors and step back to admire their work, giving no thought to completing the job in anything resembling good electrical design. They seem totally thrilled their RPC will start and run and assume that is good enough.
In all likelihood the currents are measured with a "clamp-on" type of ammeter. In that process true currents are not being measured among wildly different phase relationships in the 3 leads of an unbalanced RPC.
IMO, guys like Karl would do well to build proper RPCs before asking questions on RCM about wire sizing for bogus currents. People like Bruce with electrical backgrounds would be better able to give meaningful advice re. wire sizing if they had any notion of what the 3-phase currents in question were all about. It is impossible, as far as I know, to accurately measure unbalanced 3-phase currents with an clamp-on ammeter.
Bob Swinney
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You need to understand that Karl has a single phase (NOT 3phase!!!) 240 volt submersible pump where the run cap is topside. So the currents are measured between leads that are normally buried inside the motor. The currents he is quoting come directly from the manufacturer's service literature.
Robert Swinney wrote:

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wrote:

Your Wild Ass Guess is stunningly wrong. Karl clearly stated this was a single-phase pump a while back. See below:

The run capacitor and the motor coils (and the 180' of downlead cable in between) play hell with leading and lagging currents in the windings, and a clamp-amp isn't going to be all that accurate on oddball waveforms - even a digital one. If you need true accuracy (even though it won't accomplish anything other than bragging rights) you need to hook up an oscilloscope and watch all three lines, or spend huge bucks on a laboratory grade True RMS clamp-amp unit.
The current you really have to worry about is the line current to the pump control box, and to a lesser extent check for ground leakage which is a harbinger of a failing motor or a damaged pump lead cable.
--<< Bruce >>--
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Bruce,
I stand corrected !! My WAG was ""stunningly wrong"" about Karl's question being in regard to single-phase currents. Guess I didn't read back far enough. Your answer to Karl could have been a little more clear in as much as you addressed it to the entire group. I wonder if it confused me whether you, as a professional, were talking about single or 3-phase currents, how it may have come across to others.
Bob Swinney
wrote:

Your Wild Ass Guess is stunningly wrong. Karl clearly stated this was a single-phase pump a while back. See below:

The run capacitor and the motor coils (and the 180' of downlead cable in between) play hell with leading and lagging currents in the windings, and a clamp-amp isn't going to be all that accurate on oddball waveforms - even a digital one. If you need true accuracy (even though it won't accomplish anything other than bragging rights) you need to hook up an oscilloscope and watch all three lines, or spend huge bucks on a laboratory grade True RMS clamp-amp unit.
The current you really have to worry about is the line current to the pump control box, and to a lesser extent check for ground leakage which is a harbinger of a failing motor or a damaged pump lead cable.
--<< Bruce >>--
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...

I don't know what i did to get on your bad side. FWIW, you're right I know nothing of balancing. So, I had Fitch tune my units(three) I sent him loaded and unloaded voltages. He told me what to install.
BTW, anybody heard from Fitch lately?
Karl
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Sorry Karl. I shouldn't have personalized my reply. My mistake and I apologise. But you will note, I did say "probably lost sight of the need to properly balance . . ." having not read previous threads, as Bruce pointed out, I assumed you were talking about a 3-phase installation. (think definition of assume here ! ) So, please accept my apology, and disregard my comments as personalized. Certainly, if your 3-phase units were balanced, ala Fitch, there is nothing more to be done there.
What I was addressing was the posting in RCM of some individuals that have made rotary phase converters. They throw a few components together, more often than not without regard to good electrical practice; then set out to brag about how they built a rotary phase converter.
Bob Swinney
...

I don't know what i did to get on your bad side. FWIW, you're right I know nothing of balancing. So, I had Fitch tune my units(three) I sent him loaded and unloaded voltages. He told me what to install.
BTW, anybody heard from Fitch lately?
Karl
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you will note,

previous
(think
as
nothing more to

phase
good
And a few of them brag about a hell of a lot less than that...
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On Sat, 12 Jul 2008 18:28:53 -0500, "Karl Townsend"

Oops - well, I have the book in front of me now...
For a two wire single phase circuit: Vd = (2K x L x I) / Cm *or* Cm = (2K x L x I) / Vd
Vd - Voltage drop I - current in amps L - one-way length of circuit K - resistance in ohms of one circular mil foot of conductor     K = 12.9 for Copper 21.2 for Aluminum at 75C Cm - cross section of wire in circular mils     #10    10380     #8    16510     #6    26240     #4    41740     #2    66360     #1    83690     #1/0    105600     #2/0    133100     #3/0    167800     #4/0    211600
5 horse 1Ph well pump might be 28 A Full Load, but it should have a 200% breaker or fuse to hold on the start surges. 60A would be a conservative sizing. So we do the math for 60A and get...
42.4 x 380 X 60 / 5 volts = 193344 cm = 4/0 Aluminum
25.8 x 380 x 60 /5 volts = 117648 cm = 2/0 Copper
5 volts drop during the start surge is being rather conservative, but now you have the numbers - and you can decide how conservative you want to be.
Remember you also have that 180' of pump lead going down the well to the motor that is NOT figured in, and unless you pull the whole pump and stack out of the hole you can't change it.
2" Rigid PVC Sched 40 max fill is three 300MCM THHN/THWN or four #4/0.
Myself, I would go for a 70A or 100A sub-panel out at the wellhead. If the majority of the load is 240V you can undersize the neutral one gauge from the hots, but not under the normal minimum. 4/0 4/0 2/0 4 makes it easy to ID the neutral and ground.
That way WHEN (not if) the load grows out in that direction (*) for lights or a battery charger and block heater for the tractor, or a chlorine dosing pump because some bugs get into the well, you don't have to rework it again. And wire prices aren't going to go down much, if at all.
* - We do work for a few ranches and camps, it always does.
Oh, and if you want to move the pressure switch to the wellhead (I would, save on running those control leads and eliminate several points of failure) you need to either move one of the stored-pressure tanks to the wellhead or add a surge chamber with a needle valve in front of the pressure switch. That should smooth the pressure surges in the line enough to stop any short-cycling.
--<< Bruce >>--
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