ground wire for solar panels

[GlennWest]

Mine is not the typical solar install. Be pulling 250v per each array. Do I need a ground system? See it done on residential systems. They also put a rod in earth too but we can't do that. 

[Randyretired]

Hi Glenn, I will add my $.02 to this.  First I can't think of any reason not to ground the panel frames.  The next thing that comes to mind is 250v is dangerous and it is DC which has additional dangers.  Possibly deadly if you come in contact with it.  If you ground the frames to the RV frame that would ensure that all metal is at the same potential and would reduce the chance of a shock hazard.  So that is a good thing.  I haven't been around high voltage solar, especially on an RV to know how likely a problem is but of course at that voltage once could be the last time.  My panels on the RV are currently working around 40v so I didn't bother. 

Edited November 21, 2022 by Randyretired

[oldjohnt]

4 hours ago, GlennWest said:

Do I need a ground system? See it done on residential systems. They also put a rod in earth too but we can't do that. 

 Hi Glenn, good questions without getting too deep in the weeds I can only offer some basic theory and information: Its NOT intended to be exact or fully correct or detailed, that cant be covered in a few sentences especially to non sparkies so cut me some slack please.

DISCLAIMER  for the best answer I suggest you refer to any NEC, Solar, or RV industry codes and standards plus the owner manuals. DO NOT hang your hat on or rely on anything this old retired electrical power distribution engineer recalls, ITS BEEN TOO LONG SINCE I PRACTICED and am NOT a solar EXPERT, so with that in mind here are my thoughts:::

YES I advise a solar ""ground system"" (1) For safety,,,,,,,, (2) To eliminate voltage potential differences (keep all at same potential),,,,,,,(3) To bond panel frames to the RV's Equipment GroundING system,,,,,,,(4) Possible surge, HV or lightning protection          NOTTTTT the two wire PV output POS and NEG DC conductors..   

EXPLANATION

 What lay people simply call "Grounding" your two wire DC Solar system is NOT the same as EARTH GROUNDING of the Neutral in your homes AC distribution system. Earth grounding of the utility Neutral is for lightning and surge protection plus to keep the grid at a common low voltage reference IE MOTHER EARTH. The RV's conductive iron frame is bonded to the service pedestals EQUIPMENT GROUNDING CONDUCTOR to provide a low impedance return path FOR FAULT CURRENT and shock prevention.

 The two wire DC solar energy source (panels) are NOT referenced to MOTHER EARTH, its X Volts DC Pos to Neg, NOT X volts to mother earth.  Sure the RV's conductive iron frame can be and is used to provide a return path for the 12 VDC battery powered systems NEG by the battery NEG being connected to the iron frame. 

 THAT ALL BEING SAID like any other of the RV conductive surfaces such as its iron frame, its okay to bond the panels frame to the Equipment GroundING Conductror IE the RV frame. That keeps the RV frame and panel frames at the same voltage so there's no potential voltage difference BUT IT DOES NOT CONNECT THE PANELS PV OUTPUT + OR - DC CONDUCTORS TO THE FRAME. AFTER the solar charge controller distributes its DC to the battery bank the 12 Volt batteries may have their NEG bonded to the RV frame as discussed above. If you operate at 24 or 48 VDC  those POS and NEG DC power leads can power Inverters or 48 to 12 VDC converters to power 12 VDC coach loads  

SHORT BASICS   Sure "Ground" the frames of the panels to the RV frame and Equipment Grounding Conductor,,,,,,,Do not tie either of the panels PV DC output POS and NEG leads to frame or EGC,,,,,,,,,Use the TWO POS and NEG leads (NOT iron frame) for connection to solar charge controllers,,,,,,,,Sure on high voltage residential or commercial PV systems Equipment Grounding is used but its NOT to use earth as a conductor or to reference the PV two wire output to mother earth, its output is two wire DC     

 GROUND PER THE OWNERS MANUAL AND ANY NEC OR RV CODES AND STANDARDS is my final advice while the above is intended as educational only

 John T  BSEE,JD Too long retired EE but believe this to still be accurate. I am NOT any solar expert, so see what they have to say !!!!!!!!!!!!!!!!!!!!!!!!!!! They may agree or disagree and/or hopefully add to this as I remain ever curious and willing to learn........I look forward to their thoughts

[GlennWest]

oh, had no intention of using frame for dc negative from panels. I was asking about running a ground line to frame from panel frame.

[oldjohnt]

52 minutes ago, GlennWest said:

I was asking about running a ground line to frame from panel frame.

Thats a good idea Glenn for all the reasons I mentioned above. Of course, many RV electrical devices (solar related or otherwise) have a Grounding Lug/Terminal on their frame which should be utilized.  

 Have a good day now

 John T  Live in the RV on the shores of Lake Somervile Texas 

 

[Darryl&Rita]

1 hour ago, GlennWest said:

oh, had no intention of using frame for dc negative from panels. I was asking about running a ground line to frame from panel frame.

Given that you're putting the equivalent of Ben Franklin's key on the roof of your RV, why would you even question the need for a separate conductor? Tie the PV frames, the racks, and the RV frame together. It seems you're intent on piecing together a system, without benefit of code compliance, but you're getting outside where I'm comfortable adding anymore advice.

[GlennWest]

Out of compliance? Have breakers to isolate panels from controller. Have DC disconnects between batteries and inverters. Asked about grounding panels and seems that is needed. Where am I out of compliance? Now I am asking. I am no electrician. Also I have watched lots of youtube on solar on rv and no one mentions grounding. Curious, since we get our earth ground from the parks service, when ya'll boondock you don't have an earth ground?

Edited November 22, 2022 by GlennWest

[GlennWest]

Stupid question guys. Teton uses the chassis as 12v negative path. If I ground panels to chassis and something happens and current runs to chassis will it not fry my 12v electronics? 

[Randyretired]

The AC is also using the frame as a ground.  In order to complete a circuit the power must return to the source.  Meaning 240v. AC or 48v or 12v are all separate circuits just using one leg as a ground to keep all metal appliances at the same potential for shock hazard protection.  If any of the positives or nongrounded conductors come in contact with the ground the overcurrent (fuses or breakers) will trip for that power source.  Nothing will happen to the other sources using the ground.  

Grounding solar panels on my ground mount arrays I doubt I will follow the NEC.  This doesn't pertain to your situation but grounding panels is complex.

[oldjohnt]

5 hours ago, GlennWest said:

Stupid question guys. Teton uses the chassis as 12v negative path. If I ground panels to chassis and something happens and current runs to chassis will it not fry my 12v electronics? 

Glenn NOT a stupid question, you are wise to be curious better safe then sorry

FWIW I agree with Randys excellent advice !!!!!!!!!!!!!!!!!!!

NOPE  unless there's other serious problems and alternate current paths (weird things can happen) the fact your solar panel frames happen to be bonded to and at the same potential as the RV frame should NOT harm you RV electronics, if so then were all in big trouble lol

 The reason the RV frame (in addition to DC NEG) is also bonded to the incoming AC service utility's Equipment GroundING Conductor is in case there's a Hot L1 or L2 to Frame short there's a fault current return path so the breaker trips..........Same holds true for any shorts to the panel frames.........

 Bonding the RV frame and solar frames etc keeps them ALL at the same potential so theres no current flow or arcing going on from one to the other PLUS any hot AC shorts have a fault current return path as explained above

 If you have all your Solar DC wiring over current protected and the proper disconnects and your electronic components properly grounded and overload protected PLUS the solar panels metal frames grounded Id guess (NOT there cant know or say) youre in pretty good shape code wise and safe........

 AGAIN Consult the NEC and any RV Industry codes NOT me as Im long retired from power distribution design 

 John T   BSEE,JD  NOT any solar expert see what they have to say

 

Edited November 22, 2022 by oldjohnt

[GlennWest]

Ok, thank you. Are you sure the AC side in an rv is chassis grounded? 

[oldjohnt]

2 minutes ago, GlennWest said:

Are you sure the AC side in an rv is chassis grounded? 

YES unless its wired incorrect !!!!!!!! and if so its a hazard and serious NEC violation  !!!!!!!!!!!! The RV frame should be bonded to the incoming AC utility service Equipment GroundING Conductor. If not and there was a short and you touched the frame YOU COULD BE KILLED

Thats like NEC 101

Good questions Glenn

John T

[GlennWest]

I know when we connect to incoming ac service we are connected to ground but are we when not connected? I have not looked at it that close. 

[Randyretired]

There should be a permanent ground connection from the AC service to the frame of the RV.  When connected to the grid the ground from the panel is also connected to service ground.  Your inverters should also be grounded to the RV frame.  As John said everything grounded together so that everything is at the same potential.  This is a safety feature for shock protection.  Even in a Stix and bricks every ground should be connected and every electrical appliance should be grounded.  The ground wire going to the earth is to dissipate surges and static electricity. That wire alone doesn't provide shock protection.

[GlennWest]

Ok Just checked. It is grounded. Don't know why I thought it wasn't. My inverters will be wired straight to my breaker box input. Ultility comes in at inverters. Should I also ground my inverters to chassis also? Think I should

Edited November 23, 2022 by GlennWest

[Randyretired]

1 hour ago, GlennWest said:

Ok Just checked. It is grounded. Don't know why I thought it wasn't. My inverters will be wired straight to my breaker box input. Ultility comes in at inverters. Should I also ground my inverters to chassis also? Think I should

Yes

[GlennWest]

thank you

[oldjohnt]

16 hours ago, GlennWest said:

Ok Just checked. It is grounded. Don't know why I thought it wasn't. My inverters will be wired straight to my breaker box input. Ultility comes in at inverters. Should I also ground my inverters to chassis also? Think I should

Glenn, the answer to this gets a bit complicated and much more than most non electricians think. I cant explain it in great detail here so I will just provide a few basic rules.

1) Grounding IS NOT the same as Neutral Ground BONDING  Earth grounding of the utility neutral is for HV surge and lightning protection.. Establishment of a NG BOND with a third wire safety Equipment Grounding Conductor bonded to tools and appliances is for shock protection and to provide a current return only for FAULT CURRENT so the breaker trips and clears the fault and saves your life !!!! 

2) There can be ONLY ONE Neutral Ground Bond

3) The utility shore power NG bond takes place in the distribution which is why in an RV panel THERE IS NO NG BOND. Also the utility Neutral is to be bonded to ALL READILY AVAILAVBLE GROUNDING ELECTRODES such as copper rods driven into earth IE knows as a MADE ELECTRODE  

4) When a genset or an inverter is used and configured as a Separate Derived System to establish a grounded versus a floating system the inverter or genset or a transfer switch is where the new NG bond takes place.

5) Since in an RV theres no earth ground the RV frame is used for a substitute GROUNDING ELECTRODE.

SHORT ANSWER IS YESSSSSSSSSSSSS ground inverters or gensets etc to chassis ground !!!!

I just cant cover here what can take volumes to comprehend but I hopefully this is adequate and helps ?????????? If not post back questions

 Happy Thanksgiving

 John T  BSEE,JD Retired n rusty power distribution engineer but believe this is still accurate

[oldjohnt]

21 hours ago, GlennWest said:

I know when we connect to incoming ac service we are connected to ground but are we when not connected? I have not looked at it that close.

When NOT connected to utility theres obviously no connection of the neutral to any earth ground, however the RV frame serves as a substitute Grounding Electrode. The single Neutral Ground BOND is in that case established in the inverter or genset or transfer switch (remember NO NG BOND in RV panel)..

Hope this helps, keep asking those good questions Glenn   

John T   BSEE,JD