The "Meg" Build

Quattrohead

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Digital meters can sniff a voltage with almost no current at all so can give random readings, BUT please take care and use rated rubber gloves or tools with rated handles.....not sure duct tape wrapping is good enough LOL.
You can take a 60W regular filiment household bulb and put it where you are measuring this "leakage" voltage and see if the bulb lights up, if it does you have a serious fault, if not then it's some random leakage but I would bond everything together.
 

GSXR1000

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I disconnect the PV wires from the Array (200ft away) and still have 54V AC between rv and earth.

For the hell of it, I connected back to the grid with 50a supply, and low and behold, only 216mV between rv and earth, and no shocking when I touch it.

So does this mean I need to bond neutral/ground when not connected to grid power?
yes... the neutral and ground can not be connected in the RV panel due to the fact it becomes a sub panel when your plugged into the pedestal...
also if you put a switch style bond it needs to handle enough current to trip the 50 amp breaker
 

FilterGuy

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yes... the neutral and ground can not be connected in the RV panel due to the fact it becomes a sub panel when your plugged into the pedestal...
also if you put a switch style bond it needs to handle enough current to trip the 50 amp breaker
Correct, the NG bond for when not on shore power must be dynamic. (Bonded when not on shore power and not bonded when on shore power)

However, the NG bond from shore power may not be the thing that made the symptom go away.
- The OP has said the inverters are mounted to metal so we know the inverter is tied to chassis.
- All inverters I have ever worked with tied all AC grounds and the case ground together. It is safe to assume the ground from shore power is tied to chassis.
- Shore power will tie the Equipment Grounding Conductor of the plug to Earth ground.

Therefore, when plugged into shore power, the Chassie of the trailer is tied to earth ground. This is the same thing as when the OP tied the chassis to earth ground by pounding a screwdriver into the ground.

Could the lack of an NG ground be causing the problem the OP is investigating? Anything is possible, but I can't figure out how. It would be an interesting test to create an NG ground and see if the symptom goes away.... but if it does go away, is it fixing the problem or masking the symptom?

Is the lack of an NG ground a problem? Yes. The system should definitely have an NG ground in order to properly clear faults when hot is shorted to the equipment ground.
 

GSXR1000

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Correct, the NG bond for when not on shore power must be dynamic. (Bonded when not on shore power and not bonded when on shore power)

However, the NG bond from shore power may not be the thing that made the symptom go away.
- The OP has said the inverters are mounted to metal so we know the inverter is tied to chassis.
- All inverters I have ever worked with tied all AC grounds and the case ground together. It is safe to assume the ground from shore power is tied to chassis.
- Shore power will tie the Equipment Grounding Conductor of the plug to Earth ground.

Therefore, when plugged into shore power, the Chassie of the trailer is tied to earth ground. This is the same thing as when the OP tied the chassis to earth ground by pounding a screwdriver into the ground.

Could the lack of an NG ground be causing the problem the OP is investigating? Anything is possible, but I can't figure out how. It would be an interesting test to create an NG ground and see if the symptom goes away.... but if it does go away, is it fixing the problem or masking the symptom?

Is the lack of an NG ground a problem? Yes. The system should definitely have an NG ground in order to properly clear faults when hot is shorted to the equipment ground.
fyi... the inverts can not have a N-G tie that would be the same violation... the N-G tie can only be at service entrance panel
 

FilterGuy

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fyi... the inverts can not have a N-G tie that would be the same violation... the N-G tie can only be at service entrance panel
Somebody better tell all the manufacturers of inverters that have the dynamic N-G bond circuits about this! While they are at it, they need to tell UL to re-write UL-458.
 

Hedges

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My most recent theory was the batteries are isolated from chassis, so voltage gets bounced around by inverter, and so do PV wires.
I'm thinking battery negative should be bonded to frame (even if not used as a return path anywhere.) That could cure the low current AC coupling to frame, cause by PV wires to container having AC signal and capacitance to earth.

Separately, PV panel frames on container ought to be grounded back to trailer, in case of a fault.
 

Lt.Dan

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This thread might help, but I get a little lost when reading it. Can anyone else make sense of this thread?

 

FilterGuy

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This thread might help, but I get a little lost when reading it. Can anyone else make sense of this thread?

That thread is relating back to the N-G bond we have discussed a few times. I have tried to find out how the LV6548 deals with the bonding but have not been able to. (it is criminal how the inverter manuals often don't discuss this critical aspect of the system)

I know I have doubted the N-G bond (or lack thereof) is part of the observed problem, but let's do some experiments to find out.

However, before we play with an N-G bond, I think we need to look at how the neutral is wired. How hard would it be to disconnect the grid wires from the automatic transfer switch as shown below?

1635224916802.png

This would do two things:
1) Ensure the natural in and neutral out of the inverters are not tied together.
2) Get rid of the potential ground loop.

(BTW: What is the make/model of the transfer switch)

After the grid is disconnected from the transfer switch. See if the shocking problem is still there (pun intended). If the problem is gone, report back..... otherwise go to the next step.

The next step is to create an NG bond when the RV is in inverter mode and NOT plugged into shore power and the xfer switch is not hooked to the grid lines. As a temporary test, hook a 10 gauge wire between the ground and neutral bus in the breaker box and see if the problem still exists. Regardless of whether the issue exists still or not, put a good size 120V load on the AC and then measure to see if there is any significant current on the ground wire between the breaker box and the inverters. (If there is a current, the inverters have an internal N-G ground. If there is no current or just milliamps, the inverters do not have an internal NG ground. My guess is there will be no current)

Note: The N-G jumper in the breaker box is for the test and is NOT a permanent solution.

1635226076680.png

Next Step
@Hedges is correct that the Battery circuit should be bonded to the chassis ground. (The NEC requires it for 48V nominal systems).

For the final step. Add a wire between Battery negative and chassis ground. Let us know what happens.

My most recent theory was the batteries are isolated from chassis, so voltage gets bounced around by inverter, and so do PV wires.
This comment is what brought me back to wondering about the NG bond. Without the bond, the whole system is floating relative to chassis ground and earth ground. Could that be causing an apparent AC on the PV wires?

Without knowing a lot more about the internals of the inverter, I don't know if anchoring the AC side relative to the chassis ground will also anchor the DC side, but I would say it is possible.
 

12VoltInstalls

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a temporary test, hook a 10 gauge wire between the ground and neutral bus in the breaker box and see if the problem still exists. Regardless of whether the issue exists still or not, put a good size 120V load on the AC and then measure to see if there is any significant current on the ground wire between the breaker box and the inverters. (If there is a current, the inverters have an internal N-G ground. If there is no current or just milliamps, the inverters do not have an internal NG ground. My guess is there will be no current)
You, my friend, are eloquent
 

K8MEJ

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Disclaimer: I am not a licensed electrician or an E.E. Don't listen to me.

I've been following the thread but haven't said anything because I haven't had much to add to the conversation. I wonder something, though. If Dan disconnects from the PVs on the container (pull the wires from the container array off the RV system) and not plugged in to shore power so that he is self-contained, wouldn't his GFCI outlets in the trailer complain about there not being a NG bond?

Question #1: Do your GFCI outlets function and do they have any warning lights on them in the scenario above? I don't recall you ever noticing any issues before the external array was connected.

I use Victron gear and as we know, it has a ground relay that closes and bonds NG when it's an island and opens the relay when it's connected to an external AC source. When my system is an island, everything works fine and no "hot skin" on the RV. However, when I connected my Honda inverter gen to the AC source, my GFCI outlets weren't happy. The solution was easy and that was to bond NG at the generator with a NG bonding plug.

Question #2: If Dan connects up the external array again and replicates the "hot skin" on the RV, does it go away if you insert a NG bonding plug into an outlet somewhere in the RV? Note, this is similar to tying N and G inside the panel as FilterGuy suggests, but maybe a bit easier.

As suggested, something is seeking a return path via the chassis of the RV. The chassis connection should be the "ground" of last resort. For any current to flow, there has to be a voltage differential across a circuit, which is why bonding all the "grounds" together is important to prevent ground loops, which are voltage differences (differences in potential), which can cause some current flow, often through paths you really don't want voltage on.

Question #3: Do you have a heavy "ground" connection between your negative DC busbar(s) and the frame of the trailer? Is it a solid connection?

Question #4: In your AC electrical panel, do you have a heavy "ground" connection between your ground bus and the frame of the trailer?

I, personally, wouldn't rely on the bond between the chassis of the inverter and the metal it's mounted to. I suggest a heavy grounding wire from the inverters to the same point on the frame where you bonded your DC negative.

ALL circuits, whether DC or AC, should have their own return wire back to the system. In other words, don't rely on the chassis for your return path, especially for high-current appliances. It should be your last resort path to "ground" to keep you from burning your trailer down or getting a life-threatening shock.

When you're away from home and camping, you don't need to drive a ground rod every time you stop over somewhere. However, when you're connecting to something outside the electrical system of the camper (i.e. shore power, antennas, external arrays, etc), you need to make sure your "ground" reference is the same across all those things. In my case, when I operate my transmitters portable when camping, the return path of the signal on the coax is bonded to the frame of my RV. Most of the time, however, that's through my radio which will smoke my radio if lightning hits anywhere near where we are. In your case, given the distance between the outside array

I haven't answered where the voltage difference is originating. It might not matter depending on the amount of current. You could drive a proper ground rod for your soil type near where you park at home and bond your RV chassis to it and then measure the current flow through that ground. It could be so low that while you might feel a shock on your skin, it's just circulating currents that could be solved by the proper bonding that's been discussed. You should have this ground here for my next piece of advice anyway....

On the external array, the frames of all the panels should be well bonded to each other AND to a good Earth ground. So should the cargo container. Drive a ground rod at the container and bond those things to that rod. Then, run a heavy bare copper wire from the ground rod at the container to the ground rod at the RV. If nothing else, this will prevent any induced currents on the outside array (lightning or static build up from wind) from reaching your electronics or RV skin in the camper. You should probably also have a PV disconnect switch at the cargo container as well.

I noticed one day when it was windy and snowing here in Ohio that I could get a nasty shock from one of my antennas if I touched the shield of the coax. I quickly learned that wind can induce static charges, especially on a 265 foot long piece of wire 50 feet in the air. I don't know for certain, but dry winds blowing across the frames of the panels might do the same thing.

Sorry for the long read. I'm just trying to assimilate all the thoughts into some sort of plan. It may be bunk.
 

12VoltInstalls

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wouldn't his GFCI outlets in the trailer complain about there not being a NG bond?
No
I always thought that, too, but a few weeks back someone else’s thread had a GFCI note and I can’t remember who but hedges? or another astute fellow of the college that I trust information from corrected me, indicating that GFCI sorts between hot and neutral for its operation in the case of a ground fault. For whatever reason I didn’t know that!

Secondly the GFCI would only ‘complain’ if it were in the circuit of the fault.
 

K8MEJ

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No
I always thought that, too, but a few weeks back someone else’s thread had a GFCI note and I can’t remember who but hedges? or another astute fellow of the college that I trust information from corrected me, indicating that GFCI sorts between hot and neutral for its operation in the case of a ground fault. For whatever reason I didn’t know that!

Secondly the GFCI would only ‘complain’ if it were in the circuit of the fault.

That's interesting. I may be mistaken, then. I'm fortunate to have EE's in my family as well as master electricians. My buddy across the street is an EE + PE and works in power transmission. I'll see what they have to say. I'm not saying you're wrong, but now I need to learn more, which is what makes life interesting!

P.S., my experience was still that my GFCI's gave an error indicator when there was NG bond on my generator. I'm pretty sure the GFCI didn't allow current to pass at all. I happen to have my trailer at home right now so I can test this later.
 
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FilterGuy

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P.S., my experience was still that my GFCI's gave an error indicator when there was NG bond on my generator. I'm pretty sure the GFCI didn't allow current to pass at all. I happen to have my trailer at home right now so I can test this later.

A gfci plug (in the US) actually has two different detection circuits.

1) If there is a difference in current between the hot and neutral it will trip the circuit. (This is why using GFCI makes old house wiring that did not have a ground wire safer)
2) If there is a current on ground it will trip the circuit. (This is done through a clever technique the generates a resonance if there is current on ground. It does not actually measure ground current.)

If there are two NG bonds in the system, there will be current on the ground wire between the two bonds any time there is current on the neutral. (about half of the current that is supposed to be on the neutral will go through the ground) If there is a GFCI anywhere in this part of the circuit it will trip.

In the case of the generator with an NG bond, there was probably another NG bond someplace in the system and that was causing the GFCI to trip.
 

smoothJoey

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2) If there is a current on ground it will trip the circuit. (This is done through a clever technique the generates a resonance if there is current on ground. It does not actually measure ground current.)
Does that mean that a natural voltage gradient relative to earth could trip the GFCI device?
 

FilterGuy

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Does that mean that a natural voltage gradient relative to earth could trip the GFCI device?
I am not sure what is being asked.... What is meant by "Natural voltage gradient"

When properly set up, there should be no current on the ground wires during normal operation, so there should be no voltage gradient.
 

smoothJoey

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I am not sure what is being asked.... What is meant by "Natural voltage gradient"

When properly set up, there should be no current on the ground wires during normal operation, so there should be no voltage gradient.
I mean natural environmental electricty flowing through our wires to earth ground.
 

FilterGuy

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natural environmental electricty
Most 'natural' things that would create a current would not generate enough current to trip a GFCI, but I guess there could be unusual cases where the GFCI would trip.

A nearby lightning strike could conceivably create a magnetic pulse that could generate a current flow on the grounding circuit, but this would be so quick I am not sure the GFCI would catch it.

A continuously generated static charge from wind (Like @K8MEJ described) could generate a current flow on the grounding circuit.

If nearby equipment is generating a large magnetic field, there could be an induced current.... but it would have to be something pretty big to generate a large enough sustained current to trip the GFCI..
 

smoothJoey

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Most 'natural' things that would create a current would not generate enough current to trip a GFCI, but I guess there could be unusual cases where the GFCI would trip.

A nearby lightning strike could conceivably create a magnetic pulse that could generate a current flow on the grounding circuit, but this would be so quick I am not sure the GFCI would catch it.

A continuously generated static charge from wind (Like @K8MEJ described) could generate a current flow on the grounding circuit.

If nearby equipment is generating a large magnetic field, there could be an induced current.... but it would have to be something pretty big to generate a large enough sustained current to trip the GFCI..
Maybe the resonance signature needs to look like alternating current.
On the other hand, if dangerous dc current is flowing on the grounding conductor, regardless of origin I would like the GFCI to trip.
 

FilterGuy

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Maybe the resonance signature needs to look like alternating current.
Good point...and I don't know if it does need to be AC.

The GFCI circuits were developed and are now often required for AC issues. I am pretty sure DC was nowhere in the equation when they were being designed. It would be a happy accident if GFCI also dealt with DC issues.
 
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