Steps to diagnose electrical in submersible

Ok, here goes:
I have two identical 1/2 hp 230v 3 wire submersible pumps, one in a lake at the end of 900 feet of black poly pipe, and one in an above-ground pool at 50 ft of pvc pipe.
(the pool is the backup during a drought)

I switch the leads from one pump to the other, in a control box (specified by the pump mfr), in order to use the desired pump. With the drought here in central Texas, my lake pump was nearly dry so the pool option let my open-loop water-based AC keep running ok. Both pumps are less than 3 months old as is the control box.

I've done all the maintenance over the last decade, replaced a burned out section of wire that was underwater, ditto for a pump, done all the pool plumbing, installed the diverter valves in the original pipes, myself.

The wire to the lake pump was not tied to the pipe sufficiently when first installed by others 13 years ago so they are separate in places - the wire is type TW, 10 guage, and as a result it sunk in the mud while the polypipe just kinda laid on the bottom of the lake. The wire is caught up on stumps and rocks and may have rubbed a spot open on one of the legs. During a scuba dive a month ago I was trying to trace the wire and I came across an area where it gave me a decent buzz Despite that buzz, the pump was driving water just fine so I figured maybe the buzz was just a field effect rather than a complete short through the insulation.

A couple of days ago I was watching the water come out of the pipe from the lake when it just plumb stopped - the service panel circuit breakers did not throw. So I swapped the wires in the control box, the pump in the pool fired right up so I know the control box and the circuit breakers supply the AC, and the 2 legs coming from the AC circuit are ok.

There is no pressure tank/switch. The water flows up, around 80 feet of head over 900 feet run of 1 1/4" pipe, circulates over the copper freon loops from the AC, and then runs back down into the lake about 50 feet of head down. So it's just an open-loop thermally efficient system.
I get around 12 gallons a minute, and there are no restrictions (other than the laminar flow resistance of the poly pipe and the 1 1/4 ball valves I installed.

The pump is definitely NOT in the mud, I have it suspended above the bottom by ropes currently, and it was not every completely out of the water (never ran dry).
When I installed the last pump in the lake I removed the internal backcheck valve, and installed a separate backcheck valve with a ball valve open to air, up in the garage so that I could periodically let the water in the head flow back down to the idle pump in order to backflush the pump and it's PVC pipe cradle. (the pump is in a 4 inch pvc length so that water is drawn over the motor housing to keep it cool.

I have a multifunction meter and want to isolate the problem with the lake pump not running, without pulling the pump out/cutting the wires/hooking it up in my garage directly to the starter box if I can.

What are the steps I need to follow with the meter in order to figure out whether the motor is burned out, or if one of the legs (or more) has an opening in the insulation so that it is exposed to the water?

For 10 gauge wire, what is the maximum distance I can extend the pump out (by adding more polypipe and 10g wiring)? I need the pump to be further out in the lake to avoid heavy silt deposits.

I am considering cutting the pipe and wire where I know it is good and intact, and pulling it all out of the lake, finding the short in the wire (hopefully), heat-shrink splicing, using zip wire ties to firmly attach the wire to the pipe so the pipe stays on the bottom or even sinks into the ooze where anchors from boats are less likely to find it, and adding more pipe/wire so the pump is in deeper, less silty water.

I think I have seen a table that says a 1/2 hp 3wire submersible 230v can be out to ~1300 feet or so with 10 gauge wire?

is there a way aside from physical inspection/touch, to identify exactly where a break in the insulation is grounding out to the water?

Thanks.

I realized I could take a few readings, even if I did not know what they mean:

The pumps are Dayton 1LZU#, 10GPM, 1/2HP, 230v, 3 wire 558661 and the control box is a Franklin 1/2 HP 230v control box (1LZX3).
Red wire is start, Blk and Yel are motor leads.
Red - Yel = 1.5 ohms
Red - Blk = 3.00 M ohms
BLK - Yel = 293 to 297 K ohms
The inside of the starter box has a small table that says
Main
Blk-Yel
4.2-5.2

Start
Red-Yel
16.7-20.5

I am guessing these readings from the start box label would be "at the motor"?

What do the readings mean? Do I need to pull the pump or are there breaks in the insulation?

ok. I pulled the pump and cleaned it up, put it on a plastic stand.
The resistance matches the inside of the starter box label -
Y to B, 5 ohms
R to B, 23 ohms
and
Y to R, 18 ohms
so I think the pump is good. Comparing each of the three wires to the ground shows a flashing (1)000 which indicates no conductivity at all, as though the leads are not connected.
I haven't hooked the pump up directly to the starter box with a 6 foot patch cord to verify the pump actually runs but will try to do it tomorrow.
At this point I think it is definite that the wire's insulation has been compromised at some place under water. So I'll have to figure a way to pull the wire/polypipe out intact, without damaging anything further, locate the spot, repair it and reset the whole magilla. So situation that caused me to post this is pretty much moot. If anyone notices an error on my part I'd sure appreciate a comment.

Even when you find the short in the wire, water will have entered there and will wick it's way down the copper. It is hard to get the water out of the wire. Probably better off just getting a new string of wire.

Texarc said:

I think I have seen a table that says a 1/2 hp 3wire submersible 230v can be out to ~1300 feet or so with 10 gauge wire?

Click to expand...

1300' of 10 ga = 2.6 ohms.
At a max 5% drop at 230v this is a max. of 4.6 A.

Thatguy said:

1300' of 10 ga = 2.6 ohms.
At a max 5% drop at 230v this is a max. of 4.6 A.

Click to expand...

Not knowledgeable enough to understand this - does this mean this length is too long or that it could be longer? So I could make it even longer if I need to? As the length gets "too long" what is the effect on the pump - does it simply output less or does it cause more serious problems?

Texarc said:

Not knowledgeable enough to understand this - does this mean this length is too long or that it could be longer? So I could make it even longer if I need to? As the length gets "too long" what is the effect on the pump - does it simply output less or does it cause more serious problems?

Click to expand...

The NEC seems to use 3% and 5% as a maximum voltage drop standard. The pump manufacturer may have a different standard for his motors. If it's 5% and the motor draws 4.6 A then you can go with 1300' or less of 10 ga or larger wire.
If it were 650' then you could go with 9.2A.
Motors want a low resistance source so that when they demand more current to meet a load the voltage doesn't drop too much.
The best is to find a specification sheet for the particular pump/motor combo.

Ampacity is a separate issue and depends on the insulation temperature that the cable can endure without unduly shortening its lifetime.

Sorry for the crooked columns but I can not get them to line up.

Use the chart below to determine wire size for SUBMERSIBLE pump motors.

Single Phase Maximum Motor Cable Length (Motor Service to Entrance)

Single Phase 60 Hertz

Max length in feet of for each size of copper wire size.

Volts HP 14 12 10 8 6 4 2 0 00
115 1/3 130 210 340 540 840 1300 1960 2910 ----
115 1/2 100 160 250 390 620 960 1460 2160 ----

230 1/3 550 880 1390 2190 3400 5250 7960 ----- ----
230 1/2 400 650 1020 1610 2510 3880 5880 ----- ----
230 3/4 300 480 760 1200 1870 2890 4370 6470 ----
230 1 250 400 630 990 1540 2380 3610 5360 6520
230 1.5 190 310 480 770 1200 1870 2850 4280 5240
230 2 150 250 390 620 970 1530 2360 3620 4480
230 3 120 190 300 470 750 1190 1850 2890 3610
230 5 ---- ---- 180 280 450 710 1 110 1740 2170
230 7.5 ---- ---- ----- 200 310 490 750 1140 1410
230 10 ---- ---- ----- ----- 250 390 600 930 1160

Example: If your pump motor is 230V, 1 ph., 1.5 h.p., and 80 feet down the well, and the main power source is 400 feet from the well, you would need to use #10 wire.
A motor wired with an insufficient wire size can cause excessive voltage drop, resulting in a failure to start and excessive over-heating.

Working backwards from your table, using 1 hp, 230v, #14, 250'.
The NEC says a 1 hp 230 v motor draws 8 A

If the 250' is really a total two conductor length of 500' this would give a 4% drop in voltage, so at least for this one entry they seem to using between 3% and 5% voltage drop as a standard.

It also seems to work for 1 hp, 230v, #10, 630'.

Actually that means if you are using #14 wire, you can use it for up to a max total length of 250' from the breaker panel box to the pressure switch and then on to the submersible pump in the well.

I don't know where you get the 500' from.

Gary Slusser said:

Actually that means if you are using #14 wire, you can use it for up to a max total length of 250' from the breaker panel box to the pressure switch and then on to the submersible pump in the well.

I don't know where you get the 500' from.

Click to expand...

250' of two conductor cable is 500' of conductor, one conductor to supply the current and one conductor to return the current, so it's twice the resistance of a single strand of #14, 250' long.

The problem is that the table is for the total length of whatever gauge submersible pump power cable which can be from 2 to 4 strand, you don't double the length as you are doing. And if I were specking the cable and got out to the max length or within a few feet of max, I'd go with the next larger gauge cable. And this table is from the motor manufacturer, so I'd go with it before the NEC.

Gary, I found a similar table on goulds web site a while back (and I had to dig to find it) that will print with the columns lined up if you save it as a table instead of using copy.

I wouldn't know how to save it as a table but somewhere on my computer is a good one but I found the .txt. file first.

the saga continues....
Friday morning I am going to bypass about 150 feet of wire with new wire. I will leave the 1 1/4 " ID black polypipe in place - it is partially buried now by 6 to 10 feet of silt.
So I plan to splice in the new cable (I have a 500 ft roll of new TW 10-2 wire), and also add UP TO 400 ft of new poly pipe. Once the pump position is in a safe distance from the silt source, I want to figure out whether I've taken it too far out. In other words, how far is too far?
So once I have the cable in place, but not in the water, and not attached to the pump, and I turn on the breakers, how do I know if the drop is too much? Using a digital meter, how do verify if this pump is going to get enough juice? The manual says, for the rated voltage of 230v, the voltage must be between 210v and 250v .
A table shows the "total resistance of drop cable (OHMs) over distance for each gauge of wire. For #10, at 1250 ft there is a 2.5 drop. (I presume in ohms), and at 1600 ft #10 wire experiences a 3.0 drop.
How do i calculate this out at the end of the wire to make sure once I splice in the pump and toss it into the lake, it will run ok?
I did hook it up in the garage today, directly to the starter box, and it runs fine there. for a few seconds at least. And it's been running in the lake for several months quite nicely....

Texarc said:

For #10, at 1250 ft there is a 2.5 drop.

Click to expand...

Yes. At 1 ohm/1000' for copper at 68F, 2500' of single conductor is 2.5 ohms.
For 240v in and 210v out, your current draw can be less than 30v/2.5 = 12A.

empiric works well.
I bypassed the suspect section of 120' of underwater wire, kept the pipe. Added two 100' sections of 1 1/4 inch polypipe, and ziptied the new wire to the new pipe every 2 feet or so. Installed the pump into a new cradle made from 1 1/2 " sched 40, 40 inch legs. It was sure nice to stand up on the hill, turn the electricity on, and watch the floating pipe out in the lake to start sinking under the water, from the pump end first, and eventually start flowing out of the spout near the AC compressors.

The lake has come up 10 feet today, so I had to move fast with the splicing and the plumbing, starting at 4am when I got an alert from the LCRA about opening up a flood gate - parts of my area got 7+ inches.

So, apparently I didn't put too much cable in. (which is good since I didn't understand the previous response <G>)

People that understand pumps, wire, ohms, amps and voltages sometimes tend to get a little to technical for the novice.

If it works, don't sweat the small stuff.

Porky Cutter, MGWC
National Ground Water Assn. Certified "Master Ground Water Contractor"