Boat Dock Electrical Issue

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Old 08-18-15, 04:34 PM
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Boat Dock Electrical Issue

I have a boat dock on a lake in northeast Georgia. The dock is supplied by a 20 amp 110 GFCI 12 gauge 3 wire circuit from the house to a power pole near the water where a twist lock disconnect plugs in and leads to the floating dock. The power to the dock is for an air type boat lift, a couple of lights and a couple of 110 outlets. The dock meets all the corp or engineers electrical requirements and all electrical codes and was signed off on by a licensed electrician in March. I test the GFCI at least twice a month.

While swimming one evening, I touched the metal bunks of the boat lift and felt a tingle. I immediately searched and found a local licensed electrician to come out and inspect the dock to determine why I was feeling the tingle. While waiting a few days for the electrician, I did some troubleshooting myself and using the clamp method I read about online, discovered that I had voltage/current leakage on the conduit supplying the power the dock. I isolated the three wires in the conduit. Clamping the black and white together, the reading was 0. When I isolated the green wire and clamped it, the readings on the wire were 30 milivolts and .25 amps or 250 miliamps. i assumed I had a problem in the house with something going to ground so I flipped the main disconnect at the panel and retested. Still had the same readings on the green ground wire with all power to house in the off position. Obviously disconnected everything until the electricians arrival.

A few days later the electrician arrived and immediately said he was very familiar with the problem and it was related to stray voltage from the power company. He incidcated that the way to correct this is to disconnect the ground from the house at the lakeside power pole and drive a ground rod and connect the dock ground to this ground rod. I questioned how it would be safe to disconnect the ground to the panel since rods are really only lightening protection? His response is that by code, homes without ground wires use GFCI protection like I have on the dock and this meets code.

After he left, I continued to read and became more and more uncomfortable with my ground being disconnected to the main panel so I called the power company to ask about stray voltage/current. Guy was very nice and has agreed to dispatch a truck to check power connections to my home. Said it was very unusual to have stray voltage/current problems in my neighborhood due to the underground system but they would check. I am awaiting a response.

So my questions are:
1. Are the voltage/current readings I am getting dangerous to swimmers?
2. Why would I get a higher current reading than volts? The 250 miliamp reading is what worries me.
3. Is disconnecting the ground to panel the correct way to handle this situation?
4. Is there anything else I can try?

I have done basic electrical but realize I am over my head looking for professional advice.
 
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Old 08-18-15, 06:11 PM
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Welcome to the forums! Chatuge or Burton?? You should really have a sub panel at the dockside with power entering it, the ground isolated and a ground rod driven with separate electrode to it, so your electrician was right.

I am over in Young Harris, so we have BRMEMC, while Lake Burton will be Ga. Power Co.
 
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Old 08-18-15, 06:29 PM
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1. Are the voltage/current readings I am getting dangerous to swimmers?
Yes, anything over 6 milliamps can kill you.

2. Why would I get a higher current reading than volts? The 250 milliamps reading is what worries me.
Current (amps) and volts are two different things. Volts is best explained as pressure, while amps is the flow of electrons, aka current. Voltage does not kill you, amps do.

Are you sure you are reading your meters correctly? How did you read voltage with a clamp on meter.

Your electrician is correct in that a GFCI will function normally without a ground wire. A GFCI reads the imbalance between the hot and neutral wires. If there is more than 4-6 milliamps of imbalance on the circuit the GFCI will trip. This is for GFCI designed for protection of personnel. Other GFCI's are only designed for protection of equipment and they have a 30 milliamp threshold.

Do you know if all your dock metal is bonded together somehow? That might also be the cause of the difference of potential.
 
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Old 08-18-15, 06:57 PM
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You should really have a sub panel at the dockside with power entering it, the ground isolated and a ground rod driven with separate electrode to it, so your electrician was right.
I strongly disagree. When a sub-panel is installed to a location apart from the building where the service panel is located the equipment grounding conductor from the service panel is required to be bonded with the grounding electrode conductor (earth electrode, aka ground rod) so the addition of a sub-panel would make absolutely no difference in this situation. Remember, the sole purpose of the equipment grounding conductor is to provide a low impedance (low resistance) path back to the source of the electricity to facilitate the opening of the fuse or circuit breaker in the case of a fault.


I remember reading of a similar problem several years ago on a different forum. The moderator was/is a master electrician in his jurisdiction as well as a college-level instructor in electrician classes. Further, he is/was a member of an NEC code-making panel. He explained that this problem could be caused by a moored boat on shore power having in incorrect shore power system or it could originate at another residence or facility on the lake. Electrical systems for docks and other such installations have VERY strict requirements and it is easy to overlook something that would be acceptable on a dry land installation. You need to work with the power company AND your neighbors to find the source of this stray current.
 
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Old 08-18-15, 07:28 PM
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I think it could be the way it was worded, but the ground is isolated in the sub panel, and yes, carries back to the panel, but a supplementary grounding rod and electrode are used on sub panels. The weather resistant sub panel would make sense, because all he has is a twist lock device at present, from what I understand. Just a little safer way of making the connection.
 
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Old 08-19-15, 02:40 AM
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In my opinion you haven't worded it any better. Yes, NEUTRAL is isolated from EQUIPMENT GROUND as well as from the EARTH in a sub-panel, this is to prevent a parallel path for the normal return currents. EARTH grounding is almost exclusively for lightning protection and also to provide a zero reference point (to the earth) for the "hot" conductor(s). ALL equipment grounding conductors MUST return to the SOURCE of power as their sole purpose is to provide the low impedance path to cause a (relatively) high current flow to operate the overcurrent device in the case of a fault from the "hot" conductors to any bonded metallic object. An earth "ground" provides almost no protection when it is isolated from the source.
 
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Old 08-19-15, 04:12 AM
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isolated from the source
No one said isolate it from the source. Isolate it from the neutral and box as normal. No green screw. Etc. I think my point is being missed. The twist lock is a problem. A sub panel will alleviate that problem. Beyond that, the stray can be coming from another system...neighbor possibly.
 
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Old 08-19-15, 07:26 AM
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In any case, the solution is likely to be more earth grounding of the electrical service(s) in the vicinity. The solution of installing an earthed subpanel near the dock is a good one as this effectively extends the GEC out to the wetter soil near the lake. I would even consider actually extending the GEC in the same trench as the panel feeder and sinking a few rods along the way. You could potentially see just as good of results by adding a few additional ground rods at the house spaced 6-8' feet apart bonded with #6 copper to the existing grounding system.

It certainly could be a problem from a neighbor, but it also seems like it falls into the realm of expected neutral current travelling through the earth. That old saying about electricity "takes the path of least resistance" is total nonsense. Electricity takes all possible paths, with greater amounts flowing on the more conductive paths and lesser amounts flowing on the less conductive paths. The situation you may have here is that the earth ground at the lake -- copper wire connected to a metal dock in water -- is providing a more attractive path for the current to flow on than the ground rods attached to your electrical service or even the aluminum neutral wire running back to the power company pole. If you provide a better connection to the soil via more rods, it could significantly reduce the flow of current out through the dock. It also could help to upsize the neutral wire back to the power company transformer and to verify that all the connections are solid and tight.

For due diligence the power company should also verify that your neighbors' electrical services are well grounded too as the current could be coming from one of them.
 
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Old 08-19-15, 08:32 AM
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Try this.

Unhook the hot wire of the dock circuit from the breaker at your house panel.
Unhook the neutral of the dock circuit from the panel bus bar.
(Leave the equipment grounding conductor down to the dock attached to the panel bus bar.)

If you still get a tingle then the lake has been energized by something other than your dock branch circuit, possibly as a result of the normal grounding electrode conductors in a house electrical system or a defect in a neighbor's electrical system.

When you put things back together, reconnect the neutral before the hot.

An equipotential grounding system (suggesting for you a 12 inch square metal plate submerged in the water and bonded (here, connected with a #6 copper wire) to the boat lift framework should eliminate the tingling shock by providing an easier path for any voltage difference between the water near your boat dock and your boat dock to be reduced to near zero.
 
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Old 08-19-15, 08:47 AM
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I isolated the three wires in the conduit. Clamping the black and white together, the reading was 0. When I isolated the green wire and clamped it, the readings on the wire were 30 milivolts and .25 amps or 250 miliamps. i assumed I had a problem in the house with something going to ground so I flipped the main disconnect at the panel and retested. Still had the same readings on the green ground wire with all power to house in the off position.
One end of the voltmeter was on the green wire; where was the other lead connected? You won't feel 30mV, even in the water. If you want to measure the ground differential from the dock to the house, drive a ground rod at the dock area for your voltmeter reference. NOW, measure the green wire voltage.

He incidcated that the way to correct this is to disconnect the ground from the house at the lakeside power pole and drive a ground rod and connect the dock ground to this ground rod. I questioned how it would be safe to disconnect the ground to the panel since rods are really only lightening protection? His response is that by code, homes without ground wires use GFCI protection like I have on the dock and this meets code.
Bad idea. This is OK code wise for ungrounded branch circuits in a house but not for motors at a dock. If the motor develops a fault from hot to case, the branch OCPD would not trip, and you have a hot case. The GFCI, if it worked, would only trip when enough ground current flows.
 
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Old 08-19-15, 07:42 PM
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The twist lock is a problem.
Please explain how or why the twist-lock connection is the problem.

Everyone here KNOWS that electricity does not "return to the earth" or water in this case. Electricity flows from the source to the load and then returns to the source. The earth is NOT the source of the electricity. Ben touched upon this when he wrote:
That old saying about electricity "takes the path of least resistance" is total nonsense. Electricity takes all possible paths, with greater amounts flowing on the more conductive paths and lesser amounts flowing on the less conductive paths.
LakeMann states:
I have a boat dock on a lake in northeast Georgia. The dock is supplied by a 20 amp 110 GFCI 12 gauge 3 wire circuit from the house to a power pole near the water where a twist lock disconnect plugs in and leads to the floating dock. The power to the dock is for an air type boat lift, a couple of lights and a couple of 110 outlets.
Now other than his mistake in referring to a voltage of 110 rather than 120 it is clear that he has a normal 120 volt circuit with an equipment ground protected by a 20 ampere circuit breaker and a ground fault circuit interrupter. It is not clear, at least not to me, if the GFCI is part of the circuit breaker, a GFCI receptacle in the house with the "LOAD" terminals connected to the branch circuit feeding the twist-lock receptacle at the dock or perhaps a faceless GFCI in place of a GFCI receptacle. In any event, it IS clear that the twist-lock receptacle at the dock is a 20 ampere circuit with GFCI. Nowhere is it stated that the neutral and the equipment ground are connected at any other place but the service panel and further, unless the GFCI is incorrectly wired, the neutral and the equipment ground are most certainly isolated from each other throughout the circuit.

LakeMann goes on to state that he measures a 250 mA current in the equipment grounding conductor AND that current does not change even when he disconnects the power to the entire service panel (trips the main CB). If, under normal circumstances he had a 250 mA imbalance on the "hot" and neutral of a GFCI-protected circuit (assuming it is correctly wired) it would trip the GFCI and that is NOT happening. Further, that current on the equipment ground remains with NO POWER on the circuit wiring and even when there is no power on the service panel. That tells me the SOURCE of the current is external to LakeMann's electrical service and that there is a fault somewhere else that is supplying this current flow which is then traveling from the lake water, through the equipment grounding conductor to the solidly bonded utility neutral conductor and back to the SOURCE which is the utility's transformer. Disconnecting the equipment grounding conductor at the GFCI device or from the combined neutral/equipment ground bus in the service panel should also remove the current on the equipment grounding conductor. Note that disconnecting the EGC is NOT a cure but only a test to prove my hypothesis. The cure is to locate and remove the actual fault and THAT could be almost anywhere.
 
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Old 08-19-15, 09:32 PM
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Joel, a twist lock connection is probably not weather resistant, as I have seen them stapled to posts and the connection made from UF directly to the twist lock. Clarification or correction is in order, IMO
 
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Old 08-19-15, 09:58 PM
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I've seen weathertight twist-lock plugs and receptacles and even a non-weathertight model could be mounted to preclude the entrance of water. But I will concede that more information, including pictures, of the installation would help.
 
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Old 08-20-15, 06:40 AM
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Thank you for all the input. To clarify a few things I read in the posts. Yes, 120 circuit, yes GFCI breaker in the panel that supplies the entire circuit to the dock. It was explained to me that the twist lock type disconnect is required. It is a floating dock and the water level fluctuates and the dock has to be moved and can even go low enough where power has to be completely disconnected due to distance from power pole near the lake.

I used the clamp method around the flexible conduit at the pole and dock to take the readings. Once I had a reading, I built a connection outside the conduit to test the individual three wires using the clamp method.

I have clamped the only other three docks in my cove to test for current leakage and they all read 0.

The ground wire from the panel was disconnected at the power pole near the lake and taped up so it would not make contact with the new ground rod and dock ground. The ground and neutrals are intermingled on the same two bus bars in the panel. So from what I have read I do not have my grounds and neutrals isolated at the panel.

The dock is all metal on floats. The metal boat lift mounts extend down into the water and connect to the metal part of the dock. The electrical is connected to the dock via metal outlet and light boxes.

Again, I am not an electrician but want your advice and opions so I can better prepare to discuss with power company and probably a new electrician before this is all over.

Thanks again and keep firing away.
 
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Old 08-20-15, 09:09 AM
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The ground wire from the panel was disconnected at the power pole near the lake and taped up so it would not make contact with the new ground rod and dock ground. The ground and neutrals are intermingled on the same two bus bars in the panel. So from what I have read I do not have my grounds and neutrals isolated at the panel.
So, the .25A was measured with a clamp-on current meter at or near the panel AT THE LAKE?

We still need to know the voltage between the ground rod at you main panel at the house and the lake "DIRT". That is, take a AC voltmeter and attach one lead to a green wire going all the way to the HOUSE panel, and the other lead to lake "DIRT". Dirt means a local ground rod, re-bar or something substantial and metal, isolated from all power, that is nearby, or even in the lake. This is the voltage that you were exposed to when you felt the little shock. And, it won't be .030V.
 
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Old 08-20-15, 03:35 PM
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I used the clamp method around the flexible conduit at the pole and dock to take the readings. Once I had a reading, I built a connection outside the conduit to test the individual three wires using the clamp method.
A clamp-on ammeter may only be used on single conductors. Any reading made with multiple conductors through the "window" are suspect.

The ground wire from the panel was disconnected at the power pole near the lake and taped up so it would not make contact with the new ground rod and dock ground.
This is just plain wrong, whether or not you have the ground rod at the dock.
The ground and neutrals are intermingled on the same two bus bars in the panel.
The neutral for this circuit MUST connect to the neutral terminal of the GFCI circuit breaker. The circuit breaker will have a white "pigtail" that is connected to the neutral bus of the panel.

The ground and neutrals are intermingled on the same two bus bars in the panel.
If this is the SERVICE panel, i.e. the first circuit breaker past the kilowatt hour meter, then that is the correct configuration. If there is another circuit breaker panel, even if it has only one circuit breaker (or a similar fuse panel) then that is NOT correct.

Chandler's idea of the twist-lock connector being the source of the problem does have some merit if the connection is not made in a manner to preclude entry of rainwater to the contacts of the connection. At the very least the receptacle should have an "in-use" bubble cover or be mounted with the receptacle openings pointing downward and with some kind of cover to prevent rain from entering. The cord needs to be draped so that there is a "drip loop" that absolutely prevents water from traveling on the surface of the outer insulation into the plug.

Does the flexible interconnect cable ever lay in the water? This cable needs to be type SOOW at the least and using submarine cable would be ideal, although perhaps a bit of overkill. All the wiring in conduit should be rated THWN and the conduit should be either rigid or intermediate with threaded connections. The electrical boxes should be type FS cast boxes with integral hubs for the conduit. Any conduit connectors that have a flexible cable connection should be type CGB cord grips. The equipment grounding conductor should extend throughout the conduit system, using the conduit only for equipment grounding is not acceptable in this environment. At each junction or pull box as well as any box containing a device (switch or receptacle) the equipment grounding conductor should be electrically connected to any green grounding screw available.

A dozen or more pictures of the entire installation, both from a distance and close-ups might help us to help you. Pictures need to be in focus and well lit.. High resolution pictures uploaded to a photo hosting site and the public URL posted here is often better than uploading directly to the forum.

While probably not a huge danger at the moment this condition will NOT get better and most likely will deteriorate to a point where it IS a serious hazard.
 
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Old 08-20-15, 06:41 PM
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I will have some time this weekend to take some pics and post as well as perform the test back to panel ground rod as suggested. I have to find my ground rod at panel first. Older home so not visible at this point.

I used the clamp method as described on several websites to test shore power cords for leakage into the water. This was done near the lake in several locations on the flexible conduit. The readings were all the same. I also checked the supply wire from the house to the power pole near the lake. It had the same readings only when the twist lock was plugged in from the dock. As soon as the twist lock was unplugged, readings all returned to 0 on the supply wire from the panel to the power pole twist lock outlet near the water.

The theory, as I read it, is clamping the hot and neutral together will cancel each other out and read 0 unless the return current on the neutral is different than on the hot. In that case, you will have a reading that wiil equal the voltage/current leakage into the water that is not returning to panel. I did have a reading of zero by clamping hot and neutral together. I also clamped the individual green wire and received the readings in my first post I am concerned about. This reading on the green wire matched my initial reading of all three wires clamped together. I just googled marine electrical testing and several articles came up in how to do this test.

Sorry for my confusion on the intermingled grounds and neutrals. The gfci breaker does have the hot and neutral coneected to the breaker itself with a white spiral type wire from the breaker to the bus bar. My point was the bus bar has both neutrals and grounds in the same bus bar.

I did receive a call back from the power company today and he told me that their testing did not show any issues at their box (in my front yard). They found less than 1 volt on the ground which they believe is acceptable. He did advise me to find my ground rod at the panel to make sure it was still connected and not in poor condition. He stated that the lake is a great ground if the grounding is poor. Could this be why I only get the readings when the green ground wire is connected via the twist lock connection. I borrowed a metal detector today so I can find the ground rod outside the home and check everything this weekend.

I will take pics of the entire setup this weekend including the metal boxes and conduit and post.

Thanks again.
 
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Old 08-20-15, 06:44 PM
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Other Question

I missed the other question. Yes, the neutrals and grounds are intermingled at the primary service panel in the house that is connected to the meter.
 
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Old 08-23-15, 03:45 PM
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Pics

I took some pics of my setup and they should be attached. I also took some additional measurements.

First, I took my meter and placed one probe on bare metal of on the dock and the other in the water. I measured 0.1 volts and 35 miliamps in the water. I then put one probe on the ground wire and the other in the water and had the same reading.

Everyone may tell me the second measurement I did wasnt the correct way to do it but it made sense to me so here goes. The second measurement was to connect a long wire to unpainted metal on the dock and then clip to my meter probe. I then clipped the other probe of my meter to an insulated wire leading to a long strand of bare copper wire (18 inches) attached to the end of a wood pole which I placed in the water. I took measurements all around the dock and they were 0.1 to 0.3 volts and 25 to 35 miliamps. The further I moved away from the dock (jet ski), the lower the measurements. So, doesn't this mean the voltage/current is coming from my dock not another location?

3rd measurement. I could not find my ground rod at the service disconnect or panel (more on that later) so I connected a long wire to my ground wire that leads to the panel at the ground rod by the lake. I then drove a metal rod into the lake and measured with meter. I had 0.5 volts and 35 miliamps. I was near the dock so touched the wire to the dock to see what measurement I would get and the reading jumped to 4 volts and 155 miliamps.

I tried to find a ground rod at the service meter and at the main panel. I did not see any ground wire in panel so I assumed it is attached in the meter. I had no luck even with metal detector. The home was built in 1986. At that time could the ground be in the concrete floor? If not, I am not sure where it is. I was wanting to check to make sure everything was still connected. Does there need to be a ground at the panel. The only wires coming in the panel are two hots and the twisted neutral. I have attached pics.

I did discover another issue which I am not sure is related since my issue occurs even when the power is off. I do have a subpanel that was put in place during a remodel. The dock power is not in this panel. The grounds and neutrals are intermingled in the subpanel. The 50 amp panel is fed by two black wires from a 50 amp breaker in the main panel. A large black wire with yellow stripe is connected to the main panel ground/neutral bar and run to the sub panel and connected to the same neutral/ground bus bar (pics attached). From what I have read, this is incorrect? What do I need to do to correct?

One other measurement I did with the cover off the main panel was to clamp the neutral from the service meter. I read 4 volts and 250 miliamps which is the same reading I get when clamping the supply cord to dock.

I am not sure what to do at this point. Power company said all is good on their end but sure seems like it is coming in on their neutral/ground.
 
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Old 08-23-15, 04:24 PM
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Maybe not related to your problem but you you have things plugged into boxes that don't have in-use covers.

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Old 08-23-15, 04:47 PM
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Better than my mind conjured up with twist locks laying on the ground, but still no "in Use " covers.
 
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Old 08-23-15, 05:01 PM
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The grounds and neutrals are intermingled in the subpanel.
Yes, this should be corrected. You can run a ground wire separately from the other conductors. Just be sure to run it closely to the building, or in conduit for protection if it is #8 or smaller.

Trouble shooting this should be fairly straight forward by carefully disconnecting things one at a time and then taking measurements. When the stray voltage disappears you have found the cause. If you disconnect everything plugged in and it is still there, the fault would be in the branch circuit.
 
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Old 08-24-15, 09:35 AM
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In the main panel picture, the grounding lug to the left of the main breaker has both a copper and an aluminum wire under the same lug screw. This is bad news and should be corrected. Not only is that style of lugs only rated for one wire, the dissimilar metals are doubly bad because they will corrode each other and make a poor connection.
 
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Old 08-24-15, 03:42 PM
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In the last two pictures of post #19, is that MC or AC cable I see running through the docks?
 
 

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