Troubleshooting an GFI problem

I am having a problem with my GFI breaker tripping when I try to use my boat lift that was installed last fall.
The lift manufacturer suggested that the voltage could be too low at the remote control panel. I upgraded the wire from the main panel to the controller (310 feet) to a combination of 100 feet of #6 AL feeding 210 feet of #8 cu. The remaining wire from the controller to the lift motors (two 3/4 hp, 240V) is 50 feet of #12 cu that is run in PVC pipe along the lake bottom (there are no splices between the controller and the motors). I measured a loaded voltage (lift running lifting the boat, 11 amps) at the controller (not the motors) of 242 +/- 13 volts using the 400 volt scale on the meter and 243 +/- 5 volts using the 200 volt scale (measuring leg to ground and adding. The meter has a better accuracy on the 200 scale). The unloaded voltage was 246 volts. Based on this, I am hoping this is not a voltage drop issue.
The remote control manufacturer says it could be 1) a voltage issue or 2) moisture in the motor due to recent heavy rain. The motors are designed to be exposed. There are drain holes which are plugged (installer forget to remove them). Not sure how to check this.
After resetting the breaker, the lift will sometimes go up and down. Other times, it will trip the breaker as soon as I push the button. The subpanel breaker is 15A which was what the manufacturer recommends. The main breaker is a 50A GFI.
Any suggestions on how to troubleshoot this problem?
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Is this a new problem with an old setup? Has it been used on a regular basis since the fall? Or is it a problem with a "new" installation that has not worked right from the start?
The wire and voltages seem to be OK. The fact it sometimes immediately trips makes me suspect a ground problem. I'd check for moisture, corrosion, bad connection, that can cause the breaker to trip.
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In wrote

For the OP:
What voltage is measured between the Hot and Neutral AT the motor? What voltage is measured between Hot and Neutral AT the controll OUPUT to the motor?
A gfci does NOT care whether a ground (earth) connection is present or not. They operate simply by measuring the current in the Hot and Neutral wires and comparing them. If they are equal, all is OK. If not, then something is wrong and the gfci trips. So, somewhere, the Hot lead is feeding power to someplace other than just the N eutral lead on the setup. THAT is what trips the gfci.
There can be problems with electric motors and gfci's Now for another possibility: IF the wiring is dry all the to/from the motor, then some motors create enough phase difference in the current that it fools the gfci when it sees the lags & leads in current/voltage an inductance causes. The easiest way to do this is to exchange the motor with something resistive, like a large light bulb, electric heater, etc., and see if it still trips it; with a resistive load, it should NOT trip the breaker or blow the fuse. This might be where you are.
Details:
Check all your junctions for water. A connecton of wires should NEVER be exposed to the elements. Things like electrical tape etc will NOT keep water out permanently or at all in many cases; it needs to be treated so no water can ever touch a bare conductor. I suspect that's your problem with all those gauge changes you have. How were they done? If you say that's not the reason, why not?
If you have a 50A GFCI where you only need/is recommended to be, 15A, then you have a separate, different problem and it could in the right circumstances be a dangerous one considering what happens to the overall system. Use a 15A breaker. Either gfci will still trip at the same mismatch in current in the H & N lines; but a hard short, well then the gfci will do nothing and leave all protection up to the fuse/breaker/whatever you have, and if they are a time-delay as often used ini such places, that fuse doesn't immediately blow. The real point is, you spent a lot of money on a 50A gfci that wasn't necessary.
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wrote

** The OP has single phase 240 volt motors. No neutrals are involved

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Okay, orginal poster again. I will try to give more details an answer some of the questions raised.
This is a 240V circuit with no neutral.
The main panel has a 50A, 240v, GFI. This feeds a subpanel at the start of a dock. The two are connected with 100ft of #6AL and 100 feet of #8cu for a total run of 200 feet. The subpanel feeds the dock and the boat lift. There are 6 breakers. One breaker feeds a 1.5 hp 240V water pump. That does not trip the GFI. For that reason, I am assuming that the wires to the subpanel are not an issue.
Except for the 15A, 240V breaker feeding the boat lift, all breakers at the dock are off. This should isolate any issue to the boat lift circuit. The voltage measurements noted were taken at the inputs of the relays in the controller. A quick check today showed that the voltage on the output of the relays are the same. I have not been able to open the motors to check the voltage at the motors, These motors are not that easy to reach. They are 17 feet above the lake bottom on top of poles driven into the lake bed.
This lift was installed last fall. The wiring to thje subpanel was pre- existing. All connections are in sealed boxes rated for wet locations. All wires are individual conductors in conduit. Yesterday, I replaced the wiring from the subpanel to the controller (upgraded to #8 from #10) and verify all connections were good. I did not touch the wires from the controller to the motors. Since the fall, I ran it up and down a few feet to keep everything lubicated. No issues until yesterday. Used it about 5 times in the fall to take the boat off and it worked fine.
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*The way I understand the set up is that you have one 50 amp two pole GFI circuit breaker that provides GFI protection for everything downstream. All of the circuit breakers in the subpanel are not GFI.
I would replace the 50 amp GFI and install a regular two pole 50 amp breaker. Then I would install GFI breakers and/or outlets on the circuits in the sub-panel. Thereby keeping the GFI protection device as close to the point that needs GFI protection. It may not alleviate the problem, but at least it will make it more convenient to reset the breaker.
I would also verify that all connections at each end are tight and free of corrosion. That includes the bus bars inside the circuit breaker panels. It's too bad you can't access the motors because I would suggest checking the electrical connections for moisture which I think is your problem.
Even though the motors are rated for wet locations, moisture can still get inside and that could be enough to trip a GFI. Since the motors are not used frequently there is no heat being generated to evaporate any condensation. You may find that when summer comes and the air is warmer the problem may go away.
I have experienced a situation many years ago with HID lights over an indoor pool deck. It was a very humid environment. Each day when the lights were initially turned on the GFI circuit breakers would trip. After the breakers were reset the lights would come on and stay on for the rest of the day. Changing breakers, checking connections, replacing ballasts, etc. did nothing to correct the situation. Eventually everyone accepted the problem and a maintenance man would turn the lights on each day and then reset the breakers. The odd thing was that not all breakers tripped each day. Some would trip one day and others would trip on other days. I always thought that better ventilation might help the situation, but that was not possible in this instance.
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** John is 100% correct,(as usual) you really don't want to have GFCI protection on that length of underground cable. Every little nick and crack in the wires lends itself to GFCI tripping. As he explains, this could change when summer comes and the ground and the air dry up. Keep the GFCI protected circuits as short as possible

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** Which breaker is the GFCI? If it's the 2/15 I would replace it with a 2/20 standard breaker (for testing purposes), hang an ammeter on one of the legs and see what the starting current is, and see if it trips . It is possible to have intermittent grounding through wet windings. It's also possible that one of the motors has a starting issue. The ammeter should show exactly what's going on.
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In typed:

Have you run an Earth Ground from the lift/motor assembly that goes back to the entrance box at the house? You'll have to check your current charts for the size of the wire, being the largest wire used.
HTH,
Twayne`
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It would seem to me that the motor should be grounded back to the subpanel which in turn should be properly grounded itself.
To the OP, I'd stop focusing on voltages at the motor, which seem fine. I'd start looking for leakage current from one of the hots to ground, which is what the GFCI is looking to trip on. The suggestion of disconnecting the motor and subtituting another load to see what happens is a good one. I also agree with the advice to keep the GFCI localized to the eqpt. When you have one large one, not only are they more expensive, but then when they trip it's harder to determine the source.
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I agree that the voltage is probally not the issue. That was the starting point based on advice from the manufacturer and had to be rules out.
The motors are grounded as is the subpanel.
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replying to noname87, waltonb123 wrote: I realize this is an old post but I'm having the same issue and was wanting to know if op found the issue
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